/*
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* Copyright (C) 2008 The Android Open Source Project
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* * Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* * Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
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* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#define LOG_TAG "res_cache"
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#include "resolv_cache.h"
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#include <resolv.h>
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#include <stdarg.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <time.h>
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#include <mutex>
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#include <arpa/inet.h>
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#include <arpa/nameser.h>
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#include <errno.h>
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#include <linux/if.h>
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#include <net/if.h>
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#include <netdb.h>
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#include <android-base/logging.h>
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#include <android-base/parseint.h>
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#include <android-base/thread_annotations.h>
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#include <android/multinetwork.h> // ResNsendFlags
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#include <server_configurable_flags/get_flags.h>
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#include "res_state_ext.h"
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#include "resolv_private.h"
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// NOTE: verbose logging MUST NOT be left enabled in production binaries.
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// It floods logs at high rate, and can leak privacy-sensitive information.
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constexpr bool kDumpData = false;
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/* This code implements a small and *simple* DNS resolver cache.
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*
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* It is only used to cache DNS answers for a time defined by the smallest TTL
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* among the answer records in order to reduce DNS traffic. It is not supposed
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* to be a full DNS cache, since we plan to implement that in the future in a
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* dedicated process running on the system.
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*
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* Note that its design is kept simple very intentionally, i.e.:
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*
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* - it takes raw DNS query packet data as input, and returns raw DNS
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* answer packet data as output
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*
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* (this means that two similar queries that encode the DNS name
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* differently will be treated distinctly).
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*
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* the smallest TTL value among the answer records are used as the time
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* to keep an answer in the cache.
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*
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* this is bad, but we absolutely want to avoid parsing the answer packets
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* (and should be solved by the later full DNS cache process).
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*
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* - the implementation is just a (query-data) => (answer-data) hash table
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* with a trivial least-recently-used expiration policy.
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*
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* Doing this keeps the code simple and avoids to deal with a lot of things
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* that a full DNS cache is expected to do.
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*
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* The API is also very simple:
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*
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* - the client calls _resolv_cache_get() to obtain a handle to the cache.
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* this will initialize the cache on first usage. the result can be NULL
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* if the cache is disabled.
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*
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* - the client calls _resolv_cache_lookup() before performing a query
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*
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* if the function returns RESOLV_CACHE_FOUND, a copy of the answer data
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* has been copied into the client-provided answer buffer.
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*
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* if the function returns RESOLV_CACHE_NOTFOUND, the client should perform
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* a request normally, *then* call _resolv_cache_add() to add the received
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* answer to the cache.
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*
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* if the function returns RESOLV_CACHE_UNSUPPORTED, the client should
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* perform a request normally, and *not* call _resolv_cache_add()
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*
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* note that RESOLV_CACHE_UNSUPPORTED is also returned if the answer buffer
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* is too short to accomodate the cached result.
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*/
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/* default number of entries kept in the cache. This value has been
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* determined by browsing through various sites and counting the number
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* of corresponding requests. Keep in mind that our framework is currently
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* performing two requests per name lookup (one for IPv4, the other for IPv6)
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*
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* www.google.com 4
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* www.ysearch.com 6
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* www.amazon.com 8
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* www.nytimes.com 22
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* www.espn.com 28
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* www.msn.com 28
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* www.lemonde.fr 35
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*
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* (determined in 2009-2-17 from Paris, France, results may vary depending
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* on location)
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*
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* most high-level websites use lots of media/ad servers with different names
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* but these are generally reused when browsing through the site.
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*
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* As such, a value of 64 should be relatively comfortable at the moment.
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*
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* ******************************************
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* * NOTE - this has changed.
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* * 1) we've added IPv6 support so each dns query results in 2 responses
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* * 2) we've made this a system-wide cache, so the cost is less (it's not
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* * duplicated in each process) and the need is greater (more processes
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* * making different requests).
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* * Upping by 2x for IPv6
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* * Upping by another 5x for the centralized nature
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* *****************************************
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*/
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#define CONFIG_MAX_ENTRIES (64 * 2 * 5)
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/** BOUNDED BUFFER FORMATTING **/
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/* technical note:
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*
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* the following debugging routines are used to append data to a bounded
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* buffer they take two parameters that are:
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*
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* - p : a pointer to the current cursor position in the buffer
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* this value is initially set to the buffer's address.
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*
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* - end : the address of the buffer's limit, i.e. of the first byte
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* after the buffer. this address should never be touched.
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*
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* IMPORTANT: it is assumed that end > buffer_address, i.e.
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* that the buffer is at least one byte.
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*
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* the bprint_x() functions return the new value of 'p' after the data
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* has been appended, and also ensure the following:
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*
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* - the returned value will never be strictly greater than 'end'
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*
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* - a return value equal to 'end' means that truncation occurred
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* (in which case, end[-1] will be set to 0)
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*
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* - after returning from a bprint_x() function, the content of the buffer
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* is always 0-terminated, even in the event of truncation.
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*
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* these conventions allow you to call bprint_x() functions multiple times and
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* only check for truncation at the end of the sequence, as in:
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*
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* char buff[1000], *p = buff, *end = p + sizeof(buff);
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*
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* p = bprint_c(p, end, '"');
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* p = bprint_s(p, end, my_string);
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* p = bprint_c(p, end, '"');
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*
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* if (p >= end) {
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* // buffer was too small
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* }
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*
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* printf( "%s", buff );
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*/
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/* Defaults used for initializing res_params */
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// If successes * 100 / total_samples is less than this value, the server is considered failing
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#define SUCCESS_THRESHOLD 75
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// Sample validity in seconds. Set to -1 to disable skipping failing servers.
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#define NSSAMPLE_VALIDITY 1800
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/* add a char to a bounded buffer */
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static char* bprint_c(char* p, char* end, int c) {
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if (p < end) {
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if (p + 1 == end)
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*p++ = 0;
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else {
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*p++ = (char) c;
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*p = 0;
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}
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}
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return p;
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}
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/* add a sequence of bytes to a bounded buffer */
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static char* bprint_b(char* p, char* end, const char* buf, int len) {
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int avail = end - p;
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if (avail <= 0 || len <= 0) return p;
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if (avail > len) avail = len;
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memcpy(p, buf, avail);
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p += avail;
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if (p < end)
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p[0] = 0;
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else
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end[-1] = 0;
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return p;
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}
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/* add a string to a bounded buffer */
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static char* bprint_s(char* p, char* end, const char* str) {
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return bprint_b(p, end, str, strlen(str));
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}
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/* add a formatted string to a bounded buffer */
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static char* bprint(char* p, char* end, const char* format, ...) {
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int avail, n;
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va_list args;
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avail = end - p;
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if (avail <= 0) return p;
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va_start(args, format);
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n = vsnprintf(p, avail, format, args);
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va_end(args);
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/* certain C libraries return -1 in case of truncation */
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if (n < 0 || n > avail) n = avail;
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p += n;
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/* certain C libraries do not zero-terminate in case of truncation */
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if (p == end) p[-1] = 0;
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return p;
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}
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/* add a hex value to a bounded buffer, up to 8 digits */
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static char* bprint_hex(char* p, char* end, unsigned value, int numDigits) {
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char text[sizeof(unsigned) * 2];
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int nn = 0;
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while (numDigits-- > 0) {
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text[nn++] = "0123456789abcdef"[(value >> (numDigits * 4)) & 15];
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}
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return bprint_b(p, end, text, nn);
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}
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/* add the hexadecimal dump of some memory area to a bounded buffer */
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static char* bprint_hexdump(char* p, char* end, const uint8_t* data, int datalen) {
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int lineSize = 16;
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while (datalen > 0) {
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int avail = datalen;
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int nn;
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if (avail > lineSize) avail = lineSize;
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for (nn = 0; nn < avail; nn++) {
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if (nn > 0) p = bprint_c(p, end, ' ');
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p = bprint_hex(p, end, data[nn], 2);
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}
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for (; nn < lineSize; nn++) {
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p = bprint_s(p, end, " ");
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}
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p = bprint_s(p, end, " ");
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for (nn = 0; nn < avail; nn++) {
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int c = data[nn];
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if (c < 32 || c > 127) c = '.';
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p = bprint_c(p, end, c);
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}
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p = bprint_c(p, end, '\n');
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data += avail;
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datalen -= avail;
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}
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return p;
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}
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/* dump the content of a query of packet to the log */
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static void dump_bytes(const uint8_t* base, int len) {
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if (!kDumpData) return;
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char buff[1024];
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char *p = buff, *end = p + sizeof(buff);
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p = bprint_hexdump(p, end, base, len);
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LOG(INFO) << __func__ << ": " << buff;
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}
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static time_t _time_now(void) {
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struct timeval tv;
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gettimeofday(&tv, NULL);
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return tv.tv_sec;
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}
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/* reminder: the general format of a DNS packet is the following:
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*
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* HEADER (12 bytes)
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* QUESTION (variable)
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* ANSWER (variable)
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* AUTHORITY (variable)
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* ADDITIONNAL (variable)
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*
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* the HEADER is made of:
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*
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* ID : 16 : 16-bit unique query identification field
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*
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* QR : 1 : set to 0 for queries, and 1 for responses
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* Opcode : 4 : set to 0 for queries
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* AA : 1 : set to 0 for queries
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* TC : 1 : truncation flag, will be set to 0 in queries
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* RD : 1 : recursion desired
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*
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* RA : 1 : recursion available (0 in queries)
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* Z : 3 : three reserved zero bits
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* RCODE : 4 : response code (always 0=NOERROR in queries)
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*
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* QDCount: 16 : question count
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* ANCount: 16 : Answer count (0 in queries)
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* NSCount: 16: Authority Record count (0 in queries)
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* ARCount: 16: Additionnal Record count (0 in queries)
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*
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* the QUESTION is made of QDCount Question Record (QRs)
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* the ANSWER is made of ANCount RRs
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* the AUTHORITY is made of NSCount RRs
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* the ADDITIONNAL is made of ARCount RRs
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*
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* Each Question Record (QR) is made of:
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*
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* QNAME : variable : Query DNS NAME
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* TYPE : 16 : type of query (A=1, PTR=12, MX=15, AAAA=28, ALL=255)
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* CLASS : 16 : class of query (IN=1)
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*
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* Each Resource Record (RR) is made of:
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*
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* NAME : variable : DNS NAME
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* TYPE : 16 : type of query (A=1, PTR=12, MX=15, AAAA=28, ALL=255)
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* CLASS : 16 : class of query (IN=1)
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* TTL : 32 : seconds to cache this RR (0=none)
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* RDLENGTH: 16 : size of RDDATA in bytes
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* RDDATA : variable : RR data (depends on TYPE)
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*
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* Each QNAME contains a domain name encoded as a sequence of 'labels'
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* terminated by a zero. Each label has the following format:
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*
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* LEN : 8 : lenght of label (MUST be < 64)
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* NAME : 8*LEN : label length (must exclude dots)
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*
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* A value of 0 in the encoding is interpreted as the 'root' domain and
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* terminates the encoding. So 'www.android.com' will be encoded as:
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*
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* <3>www<7>android<3>com<0>
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*
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* Where <n> represents the byte with value 'n'
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*
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* Each NAME reflects the QNAME of the question, but has a slightly more
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* complex encoding in order to provide message compression. This is achieved
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* by using a 2-byte pointer, with format:
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*
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* TYPE : 2 : 0b11 to indicate a pointer, 0b01 and 0b10 are reserved
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* OFFSET : 14 : offset to another part of the DNS packet
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*
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* The offset is relative to the start of the DNS packet and must point
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* A pointer terminates the encoding.
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*
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* The NAME can be encoded in one of the following formats:
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*
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* - a sequence of simple labels terminated by 0 (like QNAMEs)
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* - a single pointer
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* - a sequence of simple labels terminated by a pointer
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*
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* A pointer shall always point to either a pointer of a sequence of
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* labels (which can themselves be terminated by either a 0 or a pointer)
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*
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* The expanded length of a given domain name should not exceed 255 bytes.
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*
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* NOTE: we don't parse the answer packets, so don't need to deal with NAME
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* records, only QNAMEs.
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*/
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#define DNS_HEADER_SIZE 12
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#define DNS_TYPE_A "\00\01" /* big-endian decimal 1 */
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#define DNS_TYPE_PTR "\00\014" /* big-endian decimal 12 */
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#define DNS_TYPE_MX "\00\017" /* big-endian decimal 15 */
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#define DNS_TYPE_AAAA "\00\034" /* big-endian decimal 28 */
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#define DNS_TYPE_ALL "\00\0377" /* big-endian decimal 255 */
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#define DNS_CLASS_IN "\00\01" /* big-endian decimal 1 */
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typedef struct {
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const uint8_t* base;
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const uint8_t* end;
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const uint8_t* cursor;
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} DnsPacket;
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static void _dnsPacket_init(DnsPacket* packet, const uint8_t* buff, int bufflen) {
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packet->base = buff;
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packet->end = buff + bufflen;
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packet->cursor = buff;
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}
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static void _dnsPacket_rewind(DnsPacket* packet) {
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packet->cursor = packet->base;
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}
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static void _dnsPacket_skip(DnsPacket* packet, int count) {
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const uint8_t* p = packet->cursor + count;
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if (p > packet->end) p = packet->end;
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packet->cursor = p;
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}
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static int _dnsPacket_readInt16(DnsPacket* packet) {
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const uint8_t* p = packet->cursor;
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if (p + 2 > packet->end) return -1;
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packet->cursor = p + 2;
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return (p[0] << 8) | p[1];
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}
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/** QUERY CHECKING **/
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/* check bytes in a dns packet. returns 1 on success, 0 on failure.
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* the cursor is only advanced in the case of success
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*/
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static int _dnsPacket_checkBytes(DnsPacket* packet, int numBytes, const void* bytes) {
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const uint8_t* p = packet->cursor;
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if (p + numBytes > packet->end) return 0;
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if (memcmp(p, bytes, numBytes) != 0) return 0;
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packet->cursor = p + numBytes;
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return 1;
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}
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/* parse and skip a given QNAME stored in a query packet,
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* from the current cursor position. returns 1 on success,
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* or 0 for malformed data.
|
*/
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static int _dnsPacket_checkQName(DnsPacket* packet) {
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const uint8_t* p = packet->cursor;
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const uint8_t* end = packet->end;
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for (;;) {
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int c;
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if (p >= end) break;
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c = *p++;
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if (c == 0) {
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packet->cursor = p;
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return 1;
|
}
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/* we don't expect label compression in QNAMEs */
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if (c >= 64) break;
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p += c;
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/* we rely on the bound check at the start
|
* of the loop here */
|
}
|
/* malformed data */
|
LOG(INFO) << __func__ << ": malformed QNAME";
|
return 0;
|
}
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|
/* parse and skip a given QR stored in a packet.
|
* returns 1 on success, and 0 on failure
|
*/
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static int _dnsPacket_checkQR(DnsPacket* packet) {
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if (!_dnsPacket_checkQName(packet)) return 0;
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|
/* TYPE must be one of the things we support */
|
if (!_dnsPacket_checkBytes(packet, 2, DNS_TYPE_A) &&
|
!_dnsPacket_checkBytes(packet, 2, DNS_TYPE_PTR) &&
|
!_dnsPacket_checkBytes(packet, 2, DNS_TYPE_MX) &&
|
!_dnsPacket_checkBytes(packet, 2, DNS_TYPE_AAAA) &&
|
!_dnsPacket_checkBytes(packet, 2, DNS_TYPE_ALL)) {
|
LOG(INFO) << __func__ << ": unsupported TYPE";
|
return 0;
|
}
|
/* CLASS must be IN */
|
if (!_dnsPacket_checkBytes(packet, 2, DNS_CLASS_IN)) {
|
LOG(INFO) << __func__ << ": unsupported CLASS";
|
return 0;
|
}
|
|
return 1;
|
}
|
|
/* check the header of a DNS Query packet, return 1 if it is one
|
* type of query we can cache, or 0 otherwise
|
*/
|
static int _dnsPacket_checkQuery(DnsPacket* packet) {
|
const uint8_t* p = packet->base;
|
int qdCount, anCount, dnCount, arCount;
|
|
if (p + DNS_HEADER_SIZE > packet->end) {
|
LOG(INFO) << __func__ << ": query packet too small";
|
return 0;
|
}
|
|
/* QR must be set to 0, opcode must be 0 and AA must be 0 */
|
/* RA, Z, and RCODE must be 0 */
|
if ((p[2] & 0xFC) != 0 || (p[3] & 0xCF) != 0) {
|
LOG(INFO) << __func__ << ": query packet flags unsupported";
|
return 0;
|
}
|
|
/* Note that we ignore the TC, RD, CD, and AD bits here for the
|
* following reasons:
|
*
|
* - there is no point for a query packet sent to a server
|
* to have the TC bit set, but the implementation might
|
* set the bit in the query buffer for its own needs
|
* between a _resolv_cache_lookup and a
|
* _resolv_cache_add. We should not freak out if this
|
* is the case.
|
*
|
* - we consider that the result from a query might depend on
|
* the RD, AD, and CD bits, so these bits
|
* should be used to differentiate cached result.
|
*
|
* this implies that these bits are checked when hashing or
|
* comparing query packets, but not TC
|
*/
|
|
/* ANCOUNT, DNCOUNT and ARCOUNT must be 0 */
|
qdCount = (p[4] << 8) | p[5];
|
anCount = (p[6] << 8) | p[7];
|
dnCount = (p[8] << 8) | p[9];
|
arCount = (p[10] << 8) | p[11];
|
|
if (anCount != 0 || dnCount != 0 || arCount > 1) {
|
LOG(INFO) << __func__ << ": query packet contains non-query records";
|
return 0;
|
}
|
|
if (qdCount == 0) {
|
LOG(INFO) << __func__ << ": query packet doesn't contain query record";
|
return 0;
|
}
|
|
/* Check QDCOUNT QRs */
|
packet->cursor = p + DNS_HEADER_SIZE;
|
|
for (; qdCount > 0; qdCount--)
|
if (!_dnsPacket_checkQR(packet)) return 0;
|
|
return 1;
|
}
|
|
/** QUERY DEBUGGING **/
|
static char* dnsPacket_bprintQName(DnsPacket* packet, char* bp, char* bend) {
|
const uint8_t* p = packet->cursor;
|
const uint8_t* end = packet->end;
|
int first = 1;
|
|
for (;;) {
|
int c;
|
|
if (p >= end) break;
|
|
c = *p++;
|
|
if (c == 0) {
|
packet->cursor = p;
|
return bp;
|
}
|
|
/* we don't expect label compression in QNAMEs */
|
if (c >= 64) break;
|
|
if (first)
|
first = 0;
|
else
|
bp = bprint_c(bp, bend, '.');
|
|
bp = bprint_b(bp, bend, (const char*) p, c);
|
|
p += c;
|
/* we rely on the bound check at the start
|
* of the loop here */
|
}
|
/* malformed data */
|
bp = bprint_s(bp, bend, "<MALFORMED>");
|
return bp;
|
}
|
|
static char* dnsPacket_bprintQR(DnsPacket* packet, char* p, char* end) {
|
#define QQ(x) \
|
{ DNS_TYPE_##x, #x }
|
static const struct {
|
const char* typeBytes;
|
const char* typeString;
|
} qTypes[] = {QQ(A), QQ(PTR), QQ(MX), QQ(AAAA), QQ(ALL), {NULL, NULL}};
|
int nn;
|
const char* typeString = NULL;
|
|
/* dump QNAME */
|
p = dnsPacket_bprintQName(packet, p, end);
|
|
/* dump TYPE */
|
p = bprint_s(p, end, " (");
|
|
for (nn = 0; qTypes[nn].typeBytes != NULL; nn++) {
|
if (_dnsPacket_checkBytes(packet, 2, qTypes[nn].typeBytes)) {
|
typeString = qTypes[nn].typeString;
|
break;
|
}
|
}
|
|
if (typeString != NULL)
|
p = bprint_s(p, end, typeString);
|
else {
|
int typeCode = _dnsPacket_readInt16(packet);
|
p = bprint(p, end, "UNKNOWN-%d", typeCode);
|
}
|
|
p = bprint_c(p, end, ')');
|
|
/* skip CLASS */
|
_dnsPacket_skip(packet, 2);
|
return p;
|
}
|
|
/* this function assumes the packet has already been checked */
|
static char* dnsPacket_bprintQuery(DnsPacket* packet, char* p, char* end) {
|
int qdCount;
|
|
if (packet->base[2] & 0x1) {
|
p = bprint_s(p, end, "RECURSIVE ");
|
}
|
|
_dnsPacket_skip(packet, 4);
|
qdCount = _dnsPacket_readInt16(packet);
|
_dnsPacket_skip(packet, 6);
|
|
for (; qdCount > 0; qdCount--) {
|
p = dnsPacket_bprintQR(packet, p, end);
|
}
|
return p;
|
}
|
|
/** QUERY HASHING SUPPORT
|
**
|
** THE FOLLOWING CODE ASSUMES THAT THE INPUT PACKET HAS ALREADY
|
** BEEN SUCCESFULLY CHECKED.
|
**/
|
|
/* use 32-bit FNV hash function */
|
#define FNV_MULT 16777619U
|
#define FNV_BASIS 2166136261U
|
|
static unsigned _dnsPacket_hashBytes(DnsPacket* packet, int numBytes, unsigned hash) {
|
const uint8_t* p = packet->cursor;
|
const uint8_t* end = packet->end;
|
|
while (numBytes > 0 && p < end) {
|
hash = hash * FNV_MULT ^ *p++;
|
}
|
packet->cursor = p;
|
return hash;
|
}
|
|
static unsigned _dnsPacket_hashQName(DnsPacket* packet, unsigned hash) {
|
const uint8_t* p = packet->cursor;
|
const uint8_t* end = packet->end;
|
|
for (;;) {
|
int c;
|
|
if (p >= end) { /* should not happen */
|
LOG(INFO) << __func__ << ": INTERNAL_ERROR: read-overflow";
|
break;
|
}
|
|
c = *p++;
|
|
if (c == 0) break;
|
|
if (c >= 64) {
|
LOG(INFO) << __func__ << ": INTERNAL_ERROR: malformed domain";
|
break;
|
}
|
if (p + c >= end) {
|
LOG(INFO) << __func__ << ": INTERNAL_ERROR: simple label read-overflow";
|
break;
|
}
|
while (c > 0) {
|
hash = hash * FNV_MULT ^ *p++;
|
c -= 1;
|
}
|
}
|
packet->cursor = p;
|
return hash;
|
}
|
|
static unsigned _dnsPacket_hashQR(DnsPacket* packet, unsigned hash) {
|
hash = _dnsPacket_hashQName(packet, hash);
|
hash = _dnsPacket_hashBytes(packet, 4, hash); /* TYPE and CLASS */
|
return hash;
|
}
|
|
static unsigned _dnsPacket_hashRR(DnsPacket* packet, unsigned hash) {
|
int rdlength;
|
hash = _dnsPacket_hashQR(packet, hash);
|
hash = _dnsPacket_hashBytes(packet, 4, hash); /* TTL */
|
rdlength = _dnsPacket_readInt16(packet);
|
hash = _dnsPacket_hashBytes(packet, rdlength, hash); /* RDATA */
|
return hash;
|
}
|
|
static unsigned _dnsPacket_hashQuery(DnsPacket* packet) {
|
unsigned hash = FNV_BASIS;
|
int count, arcount;
|
_dnsPacket_rewind(packet);
|
|
/* ignore the ID */
|
_dnsPacket_skip(packet, 2);
|
|
/* we ignore the TC bit for reasons explained in
|
* _dnsPacket_checkQuery().
|
*
|
* however we hash the RD bit to differentiate
|
* between answers for recursive and non-recursive
|
* queries.
|
*/
|
hash = hash * FNV_MULT ^ (packet->base[2] & 1);
|
|
/* mark the first header byte as processed */
|
_dnsPacket_skip(packet, 1);
|
|
/* process the second header byte */
|
hash = _dnsPacket_hashBytes(packet, 1, hash);
|
|
/* read QDCOUNT */
|
count = _dnsPacket_readInt16(packet);
|
|
/* assume: ANcount and NScount are 0 */
|
_dnsPacket_skip(packet, 4);
|
|
/* read ARCOUNT */
|
arcount = _dnsPacket_readInt16(packet);
|
|
/* hash QDCOUNT QRs */
|
for (; count > 0; count--) hash = _dnsPacket_hashQR(packet, hash);
|
|
/* hash ARCOUNT RRs */
|
for (; arcount > 0; arcount--) hash = _dnsPacket_hashRR(packet, hash);
|
|
return hash;
|
}
|
|
/** QUERY COMPARISON
|
**
|
** THE FOLLOWING CODE ASSUMES THAT THE INPUT PACKETS HAVE ALREADY
|
** BEEN SUCCESSFULLY CHECKED.
|
**/
|
|
static int _dnsPacket_isEqualDomainName(DnsPacket* pack1, DnsPacket* pack2) {
|
const uint8_t* p1 = pack1->cursor;
|
const uint8_t* end1 = pack1->end;
|
const uint8_t* p2 = pack2->cursor;
|
const uint8_t* end2 = pack2->end;
|
|
for (;;) {
|
int c1, c2;
|
|
if (p1 >= end1 || p2 >= end2) {
|
LOG(INFO) << __func__ << ": INTERNAL_ERROR: read-overflow";
|
break;
|
}
|
c1 = *p1++;
|
c2 = *p2++;
|
if (c1 != c2) break;
|
|
if (c1 == 0) {
|
pack1->cursor = p1;
|
pack2->cursor = p2;
|
return 1;
|
}
|
if (c1 >= 64) {
|
LOG(INFO) << __func__ << ": INTERNAL_ERROR: malformed domain";
|
break;
|
}
|
if ((p1 + c1 > end1) || (p2 + c1 > end2)) {
|
LOG(INFO) << __func__ << ": INTERNAL_ERROR: simple label read-overflow";
|
break;
|
}
|
if (memcmp(p1, p2, c1) != 0) break;
|
p1 += c1;
|
p2 += c1;
|
/* we rely on the bound checks at the start of the loop */
|
}
|
/* not the same, or one is malformed */
|
LOG(INFO) << __func__ << ": different DN";
|
return 0;
|
}
|
|
static int _dnsPacket_isEqualBytes(DnsPacket* pack1, DnsPacket* pack2, int numBytes) {
|
const uint8_t* p1 = pack1->cursor;
|
const uint8_t* p2 = pack2->cursor;
|
|
if (p1 + numBytes > pack1->end || p2 + numBytes > pack2->end) return 0;
|
|
if (memcmp(p1, p2, numBytes) != 0) return 0;
|
|
pack1->cursor += numBytes;
|
pack2->cursor += numBytes;
|
return 1;
|
}
|
|
static int _dnsPacket_isEqualQR(DnsPacket* pack1, DnsPacket* pack2) {
|
/* compare domain name encoding + TYPE + CLASS */
|
if (!_dnsPacket_isEqualDomainName(pack1, pack2) ||
|
!_dnsPacket_isEqualBytes(pack1, pack2, 2 + 2))
|
return 0;
|
|
return 1;
|
}
|
|
static int _dnsPacket_isEqualRR(DnsPacket* pack1, DnsPacket* pack2) {
|
int rdlength1, rdlength2;
|
/* compare query + TTL */
|
if (!_dnsPacket_isEqualQR(pack1, pack2) || !_dnsPacket_isEqualBytes(pack1, pack2, 4)) return 0;
|
|
/* compare RDATA */
|
rdlength1 = _dnsPacket_readInt16(pack1);
|
rdlength2 = _dnsPacket_readInt16(pack2);
|
if (rdlength1 != rdlength2 || !_dnsPacket_isEqualBytes(pack1, pack2, rdlength1)) return 0;
|
|
return 1;
|
}
|
|
static int _dnsPacket_isEqualQuery(DnsPacket* pack1, DnsPacket* pack2) {
|
int count1, count2, arcount1, arcount2;
|
|
/* compare the headers, ignore most fields */
|
_dnsPacket_rewind(pack1);
|
_dnsPacket_rewind(pack2);
|
|
/* compare RD, ignore TC, see comment in _dnsPacket_checkQuery */
|
if ((pack1->base[2] & 1) != (pack2->base[2] & 1)) {
|
LOG(INFO) << __func__ << ": different RD";
|
return 0;
|
}
|
|
if (pack1->base[3] != pack2->base[3]) {
|
LOG(INFO) << __func__ << ": different CD or AD";
|
return 0;
|
}
|
|
/* mark ID and header bytes as compared */
|
_dnsPacket_skip(pack1, 4);
|
_dnsPacket_skip(pack2, 4);
|
|
/* compare QDCOUNT */
|
count1 = _dnsPacket_readInt16(pack1);
|
count2 = _dnsPacket_readInt16(pack2);
|
if (count1 != count2 || count1 < 0) {
|
LOG(INFO) << __func__ << ": different QDCOUNT";
|
return 0;
|
}
|
|
/* assume: ANcount and NScount are 0 */
|
_dnsPacket_skip(pack1, 4);
|
_dnsPacket_skip(pack2, 4);
|
|
/* compare ARCOUNT */
|
arcount1 = _dnsPacket_readInt16(pack1);
|
arcount2 = _dnsPacket_readInt16(pack2);
|
if (arcount1 != arcount2 || arcount1 < 0) {
|
LOG(INFO) << __func__ << ": different ARCOUNT";
|
return 0;
|
}
|
|
/* compare the QDCOUNT QRs */
|
for (; count1 > 0; count1--) {
|
if (!_dnsPacket_isEqualQR(pack1, pack2)) {
|
LOG(INFO) << __func__ << ": different QR";
|
return 0;
|
}
|
}
|
|
/* compare the ARCOUNT RRs */
|
for (; arcount1 > 0; arcount1--) {
|
if (!_dnsPacket_isEqualRR(pack1, pack2)) {
|
LOG(INFO) << __func__ << ": different additional RR";
|
return 0;
|
}
|
}
|
return 1;
|
}
|
|
/* cache entry. for simplicity, 'hash' and 'hlink' are inlined in this
|
* structure though they are conceptually part of the hash table.
|
*
|
* similarly, mru_next and mru_prev are part of the global MRU list
|
*/
|
typedef struct Entry {
|
unsigned int hash; /* hash value */
|
struct Entry* hlink; /* next in collision chain */
|
struct Entry* mru_prev;
|
struct Entry* mru_next;
|
|
const uint8_t* query;
|
int querylen;
|
const uint8_t* answer;
|
int answerlen;
|
time_t expires; /* time_t when the entry isn't valid any more */
|
int id; /* for debugging purpose */
|
} Entry;
|
|
/*
|
* Find the TTL for a negative DNS result. This is defined as the minimum
|
* of the SOA records TTL and the MINIMUM-TTL field (RFC-2308).
|
*
|
* Return 0 if not found.
|
*/
|
static u_long answer_getNegativeTTL(ns_msg handle) {
|
int n, nscount;
|
u_long result = 0;
|
ns_rr rr;
|
|
nscount = ns_msg_count(handle, ns_s_ns);
|
for (n = 0; n < nscount; n++) {
|
if ((ns_parserr(&handle, ns_s_ns, n, &rr) == 0) && (ns_rr_type(rr) == ns_t_soa)) {
|
const u_char* rdata = ns_rr_rdata(rr); // find the data
|
const u_char* edata = rdata + ns_rr_rdlen(rr); // add the len to find the end
|
int len;
|
u_long ttl, rec_result = ns_rr_ttl(rr);
|
|
// find the MINIMUM-TTL field from the blob of binary data for this record
|
// skip the server name
|
len = dn_skipname(rdata, edata);
|
if (len == -1) continue; // error skipping
|
rdata += len;
|
|
// skip the admin name
|
len = dn_skipname(rdata, edata);
|
if (len == -1) continue; // error skipping
|
rdata += len;
|
|
if (edata - rdata != 5 * NS_INT32SZ) continue;
|
// skip: serial number + refresh interval + retry interval + expiry
|
rdata += NS_INT32SZ * 4;
|
// finally read the MINIMUM TTL
|
ttl = ntohl(*reinterpret_cast<const uint32_t*>(rdata));
|
if (ttl < rec_result) {
|
rec_result = ttl;
|
}
|
// Now that the record is read successfully, apply the new min TTL
|
if (n == 0 || rec_result < result) {
|
result = rec_result;
|
}
|
}
|
}
|
return result;
|
}
|
|
/*
|
* Parse the answer records and find the appropriate
|
* smallest TTL among the records. This might be from
|
* the answer records if found or from the SOA record
|
* if it's a negative result.
|
*
|
* The returned TTL is the number of seconds to
|
* keep the answer in the cache.
|
*
|
* In case of parse error zero (0) is returned which
|
* indicates that the answer shall not be cached.
|
*/
|
static u_long answer_getTTL(const void* answer, int answerlen) {
|
ns_msg handle;
|
int ancount, n;
|
u_long result, ttl;
|
ns_rr rr;
|
|
result = 0;
|
if (ns_initparse((const uint8_t*) answer, answerlen, &handle) >= 0) {
|
// get number of answer records
|
ancount = ns_msg_count(handle, ns_s_an);
|
|
if (ancount == 0) {
|
// a response with no answers? Cache this negative result.
|
result = answer_getNegativeTTL(handle);
|
} else {
|
for (n = 0; n < ancount; n++) {
|
if (ns_parserr(&handle, ns_s_an, n, &rr) == 0) {
|
ttl = ns_rr_ttl(rr);
|
if (n == 0 || ttl < result) {
|
result = ttl;
|
}
|
} else {
|
PLOG(INFO) << __func__ << ": ns_parserr failed ancount no = " << n;
|
}
|
}
|
}
|
} else {
|
PLOG(INFO) << __func__ << ": ns_initparse failed";
|
}
|
|
LOG(INFO) << __func__ << ": TTL = " << result;
|
return result;
|
}
|
|
static void entry_free(Entry* e) {
|
/* everything is allocated in a single memory block */
|
if (e) {
|
free(e);
|
}
|
}
|
|
static void entry_mru_remove(Entry* e) {
|
e->mru_prev->mru_next = e->mru_next;
|
e->mru_next->mru_prev = e->mru_prev;
|
}
|
|
static void entry_mru_add(Entry* e, Entry* list) {
|
Entry* first = list->mru_next;
|
|
e->mru_next = first;
|
e->mru_prev = list;
|
|
list->mru_next = e;
|
first->mru_prev = e;
|
}
|
|
/* compute the hash of a given entry, this is a hash of most
|
* data in the query (key) */
|
static unsigned entry_hash(const Entry* e) {
|
DnsPacket pack[1];
|
|
_dnsPacket_init(pack, e->query, e->querylen);
|
return _dnsPacket_hashQuery(pack);
|
}
|
|
/* initialize an Entry as a search key, this also checks the input query packet
|
* returns 1 on success, or 0 in case of unsupported/malformed data */
|
static int entry_init_key(Entry* e, const void* query, int querylen) {
|
DnsPacket pack[1];
|
|
memset(e, 0, sizeof(*e));
|
|
e->query = (const uint8_t*) query;
|
e->querylen = querylen;
|
e->hash = entry_hash(e);
|
|
_dnsPacket_init(pack, e->query, e->querylen);
|
|
return _dnsPacket_checkQuery(pack);
|
}
|
|
/* allocate a new entry as a cache node */
|
static Entry* entry_alloc(const Entry* init, const void* answer, int answerlen) {
|
Entry* e;
|
int size;
|
|
size = sizeof(*e) + init->querylen + answerlen;
|
e = (Entry*) calloc(size, 1);
|
if (e == NULL) return e;
|
|
e->hash = init->hash;
|
e->query = (const uint8_t*) (e + 1);
|
e->querylen = init->querylen;
|
|
memcpy((char*) e->query, init->query, e->querylen);
|
|
e->answer = e->query + e->querylen;
|
e->answerlen = answerlen;
|
|
memcpy((char*) e->answer, answer, e->answerlen);
|
|
return e;
|
}
|
|
static int entry_equals(const Entry* e1, const Entry* e2) {
|
DnsPacket pack1[1], pack2[1];
|
|
if (e1->querylen != e2->querylen) {
|
return 0;
|
}
|
_dnsPacket_init(pack1, e1->query, e1->querylen);
|
_dnsPacket_init(pack2, e2->query, e2->querylen);
|
|
return _dnsPacket_isEqualQuery(pack1, pack2);
|
}
|
|
/* We use a simple hash table with external collision lists
|
* for simplicity, the hash-table fields 'hash' and 'hlink' are
|
* inlined in the Entry structure.
|
*/
|
|
/* Maximum time for a thread to wait for an pending request */
|
constexpr int PENDING_REQUEST_TIMEOUT = 20;
|
|
typedef struct resolv_cache {
|
int max_entries;
|
int num_entries;
|
Entry mru_list;
|
int last_id;
|
Entry* entries;
|
struct pending_req_info {
|
unsigned int hash;
|
struct pending_req_info* next;
|
} pending_requests;
|
} Cache;
|
|
struct resolv_cache_info {
|
unsigned netid;
|
Cache* cache;
|
struct resolv_cache_info* next;
|
int nscount;
|
char* nameservers[MAXNS];
|
struct addrinfo* nsaddrinfo[MAXNS];
|
int revision_id; // # times the nameservers have been replaced
|
res_params params;
|
struct res_stats nsstats[MAXNS];
|
char defdname[MAXDNSRCHPATH];
|
int dnsrch_offset[MAXDNSRCH + 1]; // offsets into defdname
|
int wait_for_pending_req_timeout_count;
|
};
|
|
// A helper class for the Clang Thread Safety Analysis to deal with
|
// std::unique_lock.
|
class SCOPED_CAPABILITY ScopedAssumeLocked {
|
public:
|
ScopedAssumeLocked(std::mutex& mutex) ACQUIRE(mutex) {}
|
~ScopedAssumeLocked() RELEASE() {}
|
};
|
|
// lock protecting everything in the resolve_cache_info structs (next ptr, etc)
|
static std::mutex cache_mutex;
|
static std::condition_variable cv;
|
|
/* gets cache associated with a network, or NULL if none exists */
|
static resolv_cache* find_named_cache_locked(unsigned netid) REQUIRES(cache_mutex);
|
static int resolv_create_cache_for_net_locked(unsigned netid) REQUIRES(cache_mutex);
|
|
static void cache_flush_pending_requests_locked(struct resolv_cache* cache) {
|
resolv_cache::pending_req_info *ri, *tmp;
|
if (!cache) return;
|
|
ri = cache->pending_requests.next;
|
|
while (ri) {
|
tmp = ri;
|
ri = ri->next;
|
free(tmp);
|
}
|
|
cache->pending_requests.next = NULL;
|
cv.notify_all();
|
}
|
|
// Return true - if there is a pending request in |cache| matching |key|.
|
// Return false - if no pending request is found matching the key. Optionally
|
// link a new one if parameter append_if_not_found is true.
|
static bool cache_has_pending_request_locked(resolv_cache* cache, const Entry* key,
|
bool append_if_not_found) {
|
if (!cache || !key) return false;
|
|
resolv_cache::pending_req_info* ri = cache->pending_requests.next;
|
resolv_cache::pending_req_info* prev = &cache->pending_requests;
|
while (ri) {
|
if (ri->hash == key->hash) {
|
return true;
|
}
|
prev = ri;
|
ri = ri->next;
|
}
|
|
if (append_if_not_found) {
|
ri = (resolv_cache::pending_req_info*)calloc(1, sizeof(resolv_cache::pending_req_info));
|
if (ri) {
|
ri->hash = key->hash;
|
prev->next = ri;
|
}
|
}
|
return false;
|
}
|
|
// Notify all threads that the cache entry |key| has become available
|
static void _cache_notify_waiting_tid_locked(struct resolv_cache* cache, const Entry* key) {
|
if (!cache || !key) return;
|
|
resolv_cache::pending_req_info* ri = cache->pending_requests.next;
|
resolv_cache::pending_req_info* prev = &cache->pending_requests;
|
while (ri) {
|
if (ri->hash == key->hash) {
|
// remove item from list and destroy
|
prev->next = ri->next;
|
free(ri);
|
cv.notify_all();
|
return;
|
}
|
prev = ri;
|
ri = ri->next;
|
}
|
}
|
|
void _resolv_cache_query_failed(unsigned netid, const void* query, int querylen, uint32_t flags) {
|
// We should not notify with these flags.
|
if (flags & (ANDROID_RESOLV_NO_CACHE_STORE | ANDROID_RESOLV_NO_CACHE_LOOKUP)) {
|
return;
|
}
|
Entry key[1];
|
Cache* cache;
|
|
if (!entry_init_key(key, query, querylen)) return;
|
|
std::lock_guard guard(cache_mutex);
|
|
cache = find_named_cache_locked(netid);
|
|
if (cache) {
|
_cache_notify_waiting_tid_locked(cache, key);
|
}
|
}
|
|
static void cache_flush_locked(Cache* cache) {
|
int nn;
|
|
for (nn = 0; nn < cache->max_entries; nn++) {
|
Entry** pnode = (Entry**) &cache->entries[nn];
|
|
while (*pnode != NULL) {
|
Entry* node = *pnode;
|
*pnode = node->hlink;
|
entry_free(node);
|
}
|
}
|
|
// flush pending request
|
cache_flush_pending_requests_locked(cache);
|
|
cache->mru_list.mru_next = cache->mru_list.mru_prev = &cache->mru_list;
|
cache->num_entries = 0;
|
cache->last_id = 0;
|
|
LOG(INFO) << __func__ << ": *** DNS CACHE FLUSHED ***";
|
}
|
|
static resolv_cache* resolv_cache_create() {
|
struct resolv_cache* cache;
|
|
cache = (struct resolv_cache*) calloc(sizeof(*cache), 1);
|
if (cache) {
|
cache->max_entries = CONFIG_MAX_ENTRIES;
|
cache->entries = (Entry*) calloc(sizeof(*cache->entries), cache->max_entries);
|
if (cache->entries) {
|
cache->mru_list.mru_prev = cache->mru_list.mru_next = &cache->mru_list;
|
LOG(INFO) << __func__ << ": cache created";
|
} else {
|
free(cache);
|
cache = NULL;
|
}
|
}
|
return cache;
|
}
|
|
static void dump_query(const uint8_t* query, int querylen) {
|
if (!WOULD_LOG(VERBOSE)) return;
|
|
char temp[256], *p = temp, *end = p + sizeof(temp);
|
DnsPacket pack[1];
|
|
_dnsPacket_init(pack, query, querylen);
|
p = dnsPacket_bprintQuery(pack, p, end);
|
LOG(VERBOSE) << __func__ << ": " << temp;
|
}
|
|
static void cache_dump_mru(Cache* cache) {
|
char temp[512], *p = temp, *end = p + sizeof(temp);
|
Entry* e;
|
|
p = bprint(temp, end, "MRU LIST (%2d): ", cache->num_entries);
|
for (e = cache->mru_list.mru_next; e != &cache->mru_list; e = e->mru_next)
|
p = bprint(p, end, " %d", e->id);
|
|
LOG(INFO) << __func__ << ": " << temp;
|
}
|
|
/* This function tries to find a key within the hash table
|
* In case of success, it will return a *pointer* to the hashed key.
|
* In case of failure, it will return a *pointer* to NULL
|
*
|
* So, the caller must check '*result' to check for success/failure.
|
*
|
* The main idea is that the result can later be used directly in
|
* calls to _resolv_cache_add or _resolv_cache_remove as the 'lookup'
|
* parameter. This makes the code simpler and avoids re-searching
|
* for the key position in the htable.
|
*
|
* The result of a lookup_p is only valid until you alter the hash
|
* table.
|
*/
|
static Entry** _cache_lookup_p(Cache* cache, Entry* key) {
|
int index = key->hash % cache->max_entries;
|
Entry** pnode = (Entry**) &cache->entries[index];
|
|
while (*pnode != NULL) {
|
Entry* node = *pnode;
|
|
if (node == NULL) break;
|
|
if (node->hash == key->hash && entry_equals(node, key)) break;
|
|
pnode = &node->hlink;
|
}
|
return pnode;
|
}
|
|
/* Add a new entry to the hash table. 'lookup' must be the
|
* result of an immediate previous failed _lookup_p() call
|
* (i.e. with *lookup == NULL), and 'e' is the pointer to the
|
* newly created entry
|
*/
|
static void _cache_add_p(Cache* cache, Entry** lookup, Entry* e) {
|
*lookup = e;
|
e->id = ++cache->last_id;
|
entry_mru_add(e, &cache->mru_list);
|
cache->num_entries += 1;
|
|
LOG(INFO) << __func__ << ": entry " << e->id << " added (count=" << cache->num_entries << ")";
|
}
|
|
/* Remove an existing entry from the hash table,
|
* 'lookup' must be the result of an immediate previous
|
* and succesful _lookup_p() call.
|
*/
|
static void _cache_remove_p(Cache* cache, Entry** lookup) {
|
Entry* e = *lookup;
|
|
LOG(INFO) << __func__ << ": entry " << e->id << " removed (count=" << cache->num_entries - 1
|
<< ")";
|
|
entry_mru_remove(e);
|
*lookup = e->hlink;
|
entry_free(e);
|
cache->num_entries -= 1;
|
}
|
|
/* Remove the oldest entry from the hash table.
|
*/
|
static void _cache_remove_oldest(Cache* cache) {
|
Entry* oldest = cache->mru_list.mru_prev;
|
Entry** lookup = _cache_lookup_p(cache, oldest);
|
|
if (*lookup == NULL) { /* should not happen */
|
LOG(INFO) << __func__ << ": OLDEST NOT IN HTABLE ?";
|
return;
|
}
|
LOG(INFO) << __func__ << ": Cache full - removing oldest";
|
dump_query(oldest->query, oldest->querylen);
|
_cache_remove_p(cache, lookup);
|
}
|
|
/* Remove all expired entries from the hash table.
|
*/
|
static void _cache_remove_expired(Cache* cache) {
|
Entry* e;
|
time_t now = _time_now();
|
|
for (e = cache->mru_list.mru_next; e != &cache->mru_list;) {
|
// Entry is old, remove
|
if (now >= e->expires) {
|
Entry** lookup = _cache_lookup_p(cache, e);
|
if (*lookup == NULL) { /* should not happen */
|
LOG(INFO) << __func__ << ": ENTRY NOT IN HTABLE ?";
|
return;
|
}
|
e = e->mru_next;
|
_cache_remove_p(cache, lookup);
|
} else {
|
e = e->mru_next;
|
}
|
}
|
}
|
|
// gets a resolv_cache_info associated with a network, or NULL if not found
|
static resolv_cache_info* find_cache_info_locked(unsigned netid) REQUIRES(cache_mutex);
|
|
ResolvCacheStatus _resolv_cache_lookup(unsigned netid, const void* query, int querylen,
|
void* answer, int answersize, int* answerlen,
|
uint32_t flags) {
|
// Skip cache lookup, return RESOLV_CACHE_NOTFOUND directly so that it is
|
// possible to cache the answer of this query.
|
// If ANDROID_RESOLV_NO_CACHE_STORE is set, return RESOLV_CACHE_SKIP to skip possible cache
|
// storing.
|
// (b/150371903): ANDROID_RESOLV_NO_CACHE_STORE should imply ANDROID_RESOLV_NO_CACHE_LOOKUP
|
// to avoid side channel attack.
|
if (flags & (ANDROID_RESOLV_NO_CACHE_LOOKUP | ANDROID_RESOLV_NO_CACHE_STORE)) {
|
return flags & ANDROID_RESOLV_NO_CACHE_STORE ? RESOLV_CACHE_SKIP : RESOLV_CACHE_NOTFOUND;
|
}
|
Entry key;
|
Entry** lookup;
|
Entry* e;
|
time_t now;
|
Cache* cache;
|
|
LOG(INFO) << __func__ << ": lookup";
|
dump_query((u_char*) query, querylen);
|
|
/* we don't cache malformed queries */
|
if (!entry_init_key(&key, query, querylen)) {
|
LOG(INFO) << __func__ << ": unsupported query";
|
return RESOLV_CACHE_UNSUPPORTED;
|
}
|
/* lookup cache */
|
std::unique_lock lock(cache_mutex);
|
ScopedAssumeLocked assume_lock(cache_mutex);
|
cache = find_named_cache_locked(netid);
|
if (cache == NULL) {
|
return RESOLV_CACHE_UNSUPPORTED;
|
}
|
|
/* see the description of _lookup_p to understand this.
|
* the function always return a non-NULL pointer.
|
*/
|
lookup = _cache_lookup_p(cache, &key);
|
e = *lookup;
|
|
if (e == NULL) {
|
LOG(INFO) << __func__ << ": NOT IN CACHE";
|
if (!cache_has_pending_request_locked(cache, &key, true)) {
|
return RESOLV_CACHE_NOTFOUND;
|
|
} else {
|
LOG(INFO) << __func__ << ": Waiting for previous request";
|
// wait until (1) timeout OR
|
// (2) cv is notified AND no pending request matching the |key|
|
// (cv notifier should delete pending request before sending notification.)
|
bool ret = cv.wait_for(lock, std::chrono::seconds(PENDING_REQUEST_TIMEOUT),
|
[netid, &cache, &key]() REQUIRES(cache_mutex) {
|
// Must update cache as it could have been deleted
|
cache = find_named_cache_locked(netid);
|
return !cache_has_pending_request_locked(cache, &key, false);
|
});
|
if (!cache) {
|
return RESOLV_CACHE_NOTFOUND;
|
}
|
if (ret == false) {
|
resolv_cache_info* info = find_cache_info_locked(netid);
|
if (info != NULL) {
|
info->wait_for_pending_req_timeout_count++;
|
}
|
}
|
lookup = _cache_lookup_p(cache, &key);
|
e = *lookup;
|
if (e == NULL) {
|
return RESOLV_CACHE_NOTFOUND;
|
}
|
}
|
}
|
|
now = _time_now();
|
|
/* remove stale entries here */
|
if (now >= e->expires) {
|
LOG(INFO) << __func__ << ": NOT IN CACHE (STALE ENTRY " << *lookup << "DISCARDED)";
|
dump_query(e->query, e->querylen);
|
_cache_remove_p(cache, lookup);
|
return RESOLV_CACHE_NOTFOUND;
|
}
|
|
*answerlen = e->answerlen;
|
if (e->answerlen > answersize) {
|
/* NOTE: we return UNSUPPORTED if the answer buffer is too short */
|
LOG(INFO) << __func__ << ": ANSWER TOO LONG";
|
return RESOLV_CACHE_UNSUPPORTED;
|
}
|
|
memcpy(answer, e->answer, e->answerlen);
|
|
/* bump up this entry to the top of the MRU list */
|
if (e != cache->mru_list.mru_next) {
|
entry_mru_remove(e);
|
entry_mru_add(e, &cache->mru_list);
|
}
|
|
LOG(INFO) << __func__ << ": FOUND IN CACHE entry=" << e;
|
return RESOLV_CACHE_FOUND;
|
}
|
|
void _resolv_cache_add(unsigned netid, const void* query, int querylen, const void* answer,
|
int answerlen) {
|
Entry key[1];
|
Entry* e;
|
Entry** lookup;
|
u_long ttl;
|
Cache* cache = NULL;
|
|
/* don't assume that the query has already been cached
|
*/
|
if (!entry_init_key(key, query, querylen)) {
|
LOG(INFO) << __func__ << ": passed invalid query?";
|
return;
|
}
|
|
std::lock_guard guard(cache_mutex);
|
|
cache = find_named_cache_locked(netid);
|
if (cache == NULL) {
|
return;
|
}
|
|
LOG(INFO) << __func__ << ": query:";
|
dump_query((u_char*)query, querylen);
|
res_pquery((u_char*)answer, answerlen);
|
if (kDumpData) {
|
LOG(INFO) << __func__ << ": answer:";
|
dump_bytes((u_char*)answer, answerlen);
|
}
|
|
lookup = _cache_lookup_p(cache, key);
|
e = *lookup;
|
|
// Should only happen on ANDROID_RESOLV_NO_CACHE_LOOKUP
|
if (e != NULL) {
|
LOG(INFO) << __func__ << ": ALREADY IN CACHE (" << e << ") ? IGNORING ADD";
|
_cache_notify_waiting_tid_locked(cache, key);
|
return;
|
}
|
|
if (cache->num_entries >= cache->max_entries) {
|
_cache_remove_expired(cache);
|
if (cache->num_entries >= cache->max_entries) {
|
_cache_remove_oldest(cache);
|
}
|
// TODO: It looks useless, remove below code after having test to prove it.
|
lookup = _cache_lookup_p(cache, key);
|
e = *lookup;
|
if (e != NULL) {
|
LOG(INFO) << __func__ << ": ALREADY IN CACHE (" << e << ") ? IGNORING ADD";
|
_cache_notify_waiting_tid_locked(cache, key);
|
return;
|
}
|
}
|
|
ttl = answer_getTTL(answer, answerlen);
|
if (ttl > 0) {
|
e = entry_alloc(key, answer, answerlen);
|
if (e != NULL) {
|
e->expires = ttl + _time_now();
|
_cache_add_p(cache, lookup, e);
|
}
|
}
|
|
cache_dump_mru(cache);
|
_cache_notify_waiting_tid_locked(cache, key);
|
}
|
|
// Head of the list of caches.
|
static struct resolv_cache_info res_cache_list GUARDED_BY(cache_mutex);
|
|
// insert resolv_cache_info into the list of resolv_cache_infos
|
static void insert_cache_info_locked(resolv_cache_info* cache_info);
|
// creates a resolv_cache_info
|
static resolv_cache_info* create_cache_info();
|
// empty the nameservers set for the named cache
|
static void free_nameservers_locked(resolv_cache_info* cache_info);
|
// return 1 if the provided list of name servers differs from the list of name servers
|
// currently attached to the provided cache_info
|
static int resolv_is_nameservers_equal_locked(resolv_cache_info* cache_info, const char** servers,
|
int numservers);
|
// clears the stats samples contained withing the given cache_info
|
static void res_cache_clear_stats_locked(resolv_cache_info* cache_info);
|
|
// public API for netd to query if name server is set on specific netid
|
bool resolv_has_nameservers(unsigned netid) {
|
std::lock_guard guard(cache_mutex);
|
resolv_cache_info* info = find_cache_info_locked(netid);
|
return (info != nullptr) && (info->nscount > 0);
|
}
|
|
static int resolv_create_cache_for_net_locked(unsigned netid) {
|
resolv_cache* cache = find_named_cache_locked(netid);
|
// Should not happen
|
if (cache) {
|
LOG(ERROR) << __func__ << ": Cache is already created, netId: " << netid;
|
return -EEXIST;
|
}
|
|
resolv_cache_info* cache_info = create_cache_info();
|
if (!cache_info) return -ENOMEM;
|
cache = resolv_cache_create();
|
if (!cache) {
|
free(cache_info);
|
return -ENOMEM;
|
}
|
cache_info->cache = cache;
|
cache_info->netid = netid;
|
insert_cache_info_locked(cache_info);
|
|
return 0;
|
}
|
|
int resolv_create_cache_for_net(unsigned netid) {
|
std::lock_guard guard(cache_mutex);
|
return resolv_create_cache_for_net_locked(netid);
|
}
|
|
void resolv_delete_cache_for_net(unsigned netid) {
|
std::lock_guard guard(cache_mutex);
|
|
struct resolv_cache_info* prev_cache_info = &res_cache_list;
|
|
while (prev_cache_info->next) {
|
struct resolv_cache_info* cache_info = prev_cache_info->next;
|
|
if (cache_info->netid == netid) {
|
prev_cache_info->next = cache_info->next;
|
cache_flush_locked(cache_info->cache);
|
free(cache_info->cache->entries);
|
free(cache_info->cache);
|
free_nameservers_locked(cache_info);
|
free(cache_info);
|
break;
|
}
|
|
prev_cache_info = prev_cache_info->next;
|
}
|
}
|
|
std::vector<unsigned> resolv_list_caches() {
|
std::lock_guard guard(cache_mutex);
|
struct resolv_cache_info* cache_info = res_cache_list.next;
|
std::vector<unsigned> result;
|
while (cache_info) {
|
result.push_back(cache_info->netid);
|
cache_info = cache_info->next;
|
}
|
return result;
|
}
|
|
static resolv_cache_info* create_cache_info() {
|
return (struct resolv_cache_info*) calloc(sizeof(struct resolv_cache_info), 1);
|
}
|
|
// TODO: convert this to a simple and efficient C++ container.
|
static void insert_cache_info_locked(struct resolv_cache_info* cache_info) {
|
struct resolv_cache_info* last;
|
for (last = &res_cache_list; last->next; last = last->next) {}
|
last->next = cache_info;
|
}
|
|
static resolv_cache* find_named_cache_locked(unsigned netid) {
|
resolv_cache_info* info = find_cache_info_locked(netid);
|
if (info != NULL) return info->cache;
|
return NULL;
|
}
|
|
static resolv_cache_info* find_cache_info_locked(unsigned netid) {
|
struct resolv_cache_info* cache_info = res_cache_list.next;
|
|
while (cache_info) {
|
if (cache_info->netid == netid) {
|
break;
|
}
|
|
cache_info = cache_info->next;
|
}
|
return cache_info;
|
}
|
|
static void resolv_set_default_params(res_params* params) {
|
params->sample_validity = NSSAMPLE_VALIDITY;
|
params->success_threshold = SUCCESS_THRESHOLD;
|
params->min_samples = 0;
|
params->max_samples = 0;
|
params->base_timeout_msec = 0; // 0 = legacy algorithm
|
params->retry_count = 0;
|
}
|
|
static void resolv_set_experiment_params(res_params* params) {
|
using android::base::ParseInt;
|
using server_configurable_flags::GetServerConfigurableFlag;
|
|
if (params->retry_count == 0) {
|
params->retry_count = RES_DFLRETRY;
|
ParseInt(GetServerConfigurableFlag("netd_native", "retry_count", ""), ¶ms->retry_count);
|
}
|
|
if (params->base_timeout_msec == 0) {
|
params->base_timeout_msec = RES_TIMEOUT;
|
ParseInt(GetServerConfigurableFlag("netd_native", "retransmission_time_interval", ""),
|
¶ms->base_timeout_msec);
|
}
|
}
|
|
int resolv_set_nameservers_for_net(unsigned netid, const char** servers, const int numservers,
|
const char* domains, const res_params* params) {
|
char* cp;
|
int* offset;
|
struct addrinfo* nsaddrinfo[MAXNS];
|
|
if (numservers > MAXNS) {
|
LOG(ERROR) << __func__ << ": numservers=" << numservers << ", MAXNS=" << MAXNS;
|
return E2BIG;
|
}
|
|
// Parse the addresses before actually locking or changing any state, in case there is an error.
|
// As a side effect this also reduces the time the lock is kept.
|
char sbuf[NI_MAXSERV];
|
snprintf(sbuf, sizeof(sbuf), "%u", NAMESERVER_PORT);
|
for (int i = 0; i < numservers; i++) {
|
// The addrinfo structures allocated here are freed in free_nameservers_locked().
|
const addrinfo hints = {
|
.ai_family = AF_UNSPEC, .ai_socktype = SOCK_DGRAM, .ai_flags = AI_NUMERICHOST};
|
int rt = getaddrinfo_numeric(servers[i], sbuf, hints, &nsaddrinfo[i]);
|
if (rt != 0) {
|
for (int j = 0; j < i; j++) {
|
freeaddrinfo(nsaddrinfo[j]);
|
}
|
LOG(INFO) << __func__ << ": getaddrinfo_numeric(" << servers[i]
|
<< ") = " << gai_strerror(rt);
|
return EINVAL;
|
}
|
}
|
|
std::lock_guard guard(cache_mutex);
|
|
resolv_cache_info* cache_info = find_cache_info_locked(netid);
|
|
if (cache_info == NULL) return ENONET;
|
|
uint8_t old_max_samples = cache_info->params.max_samples;
|
if (params != NULL) {
|
cache_info->params = *params;
|
} else {
|
resolv_set_default_params(&cache_info->params);
|
}
|
resolv_set_experiment_params(&cache_info->params);
|
if (!resolv_is_nameservers_equal_locked(cache_info, servers, numservers)) {
|
// free current before adding new
|
free_nameservers_locked(cache_info);
|
for (int i = 0; i < numservers; i++) {
|
cache_info->nsaddrinfo[i] = nsaddrinfo[i];
|
cache_info->nameservers[i] = strdup(servers[i]);
|
LOG(INFO) << __func__ << ": netid = " << netid << ", addr = " << servers[i];
|
}
|
cache_info->nscount = numservers;
|
|
// Clear the NS statistics because the mapping to nameservers might have changed.
|
res_cache_clear_stats_locked(cache_info);
|
|
// increment the revision id to ensure that sample state is not written back if the
|
// servers change; in theory it would suffice to do so only if the servers or
|
// max_samples actually change, in practice the overhead of checking is higher than the
|
// cost, and overflows are unlikely
|
++cache_info->revision_id;
|
} else {
|
if (cache_info->params.max_samples != old_max_samples) {
|
// If the maximum number of samples changes, the overhead of keeping the most recent
|
// samples around is not considered worth the effort, so they are cleared instead.
|
// All other parameters do not affect shared state: Changing these parameters does
|
// not invalidate the samples, as they only affect aggregation and the conditions
|
// under which servers are considered usable.
|
res_cache_clear_stats_locked(cache_info);
|
++cache_info->revision_id;
|
}
|
for (int j = 0; j < numservers; j++) {
|
freeaddrinfo(nsaddrinfo[j]);
|
}
|
}
|
|
// Always update the search paths, since determining whether they actually changed is
|
// complex due to the zero-padding, and probably not worth the effort. Cache-flushing
|
// however is not necessary, since the stored cache entries do contain the domain, not
|
// just the host name.
|
strlcpy(cache_info->defdname, domains, sizeof(cache_info->defdname));
|
if ((cp = strchr(cache_info->defdname, '\n')) != NULL) *cp = '\0';
|
LOG(INFO) << __func__ << ": domains=\"" << cache_info->defdname << "\"";
|
|
cp = cache_info->defdname;
|
offset = cache_info->dnsrch_offset;
|
while (offset < cache_info->dnsrch_offset + MAXDNSRCH) {
|
while (*cp == ' ' || *cp == '\t') /* skip leading white space */
|
cp++;
|
if (*cp == '\0') /* stop if nothing more to do */
|
break;
|
*offset++ = cp - cache_info->defdname; /* record this search domain */
|
while (*cp) { /* zero-terminate it */
|
if (*cp == ' ' || *cp == '\t') {
|
*cp++ = '\0';
|
break;
|
}
|
cp++;
|
}
|
}
|
*offset = -1; /* cache_info->dnsrch_offset has MAXDNSRCH+1 items */
|
|
return 0;
|
}
|
|
static int resolv_is_nameservers_equal_locked(resolv_cache_info* cache_info, const char** servers,
|
int numservers) {
|
if (cache_info->nscount != numservers) {
|
return 0;
|
}
|
|
// Compare each name server against current name servers.
|
// TODO: this is incorrect if the list of current or previous nameservers
|
// contains duplicates. This does not really matter because the framework
|
// filters out duplicates, but we should probably fix it. It's also
|
// insensitive to the order of the nameservers; we should probably fix that
|
// too.
|
for (int i = 0; i < numservers; i++) {
|
for (int j = 0;; j++) {
|
if (j >= numservers) {
|
return 0;
|
}
|
if (strcmp(cache_info->nameservers[i], servers[j]) == 0) {
|
break;
|
}
|
}
|
}
|
|
return 1;
|
}
|
|
static void free_nameservers_locked(resolv_cache_info* cache_info) {
|
int i;
|
for (i = 0; i < cache_info->nscount; i++) {
|
free(cache_info->nameservers[i]);
|
cache_info->nameservers[i] = NULL;
|
if (cache_info->nsaddrinfo[i] != NULL) {
|
freeaddrinfo(cache_info->nsaddrinfo[i]);
|
cache_info->nsaddrinfo[i] = NULL;
|
}
|
cache_info->nsstats[i].sample_count = cache_info->nsstats[i].sample_next = 0;
|
}
|
cache_info->nscount = 0;
|
res_cache_clear_stats_locked(cache_info);
|
++cache_info->revision_id;
|
}
|
|
void _resolv_populate_res_for_net(res_state statp) {
|
if (statp == NULL) {
|
return;
|
}
|
LOG(INFO) << __func__ << ": netid=" << statp->netid;
|
|
std::lock_guard guard(cache_mutex);
|
resolv_cache_info* info = find_cache_info_locked(statp->netid);
|
if (info != NULL) {
|
int nserv;
|
struct addrinfo* ai;
|
for (nserv = 0; nserv < MAXNS; nserv++) {
|
ai = info->nsaddrinfo[nserv];
|
if (ai == NULL) {
|
break;
|
}
|
|
if ((size_t) ai->ai_addrlen <= sizeof(statp->_u._ext.ext->nsaddrs[0])) {
|
if (statp->_u._ext.ext != NULL) {
|
memcpy(&statp->_u._ext.ext->nsaddrs[nserv], ai->ai_addr, ai->ai_addrlen);
|
statp->nsaddr_list[nserv].sin_family = AF_UNSPEC;
|
} else {
|
if ((size_t) ai->ai_addrlen <= sizeof(statp->nsaddr_list[0])) {
|
memcpy(&statp->nsaddr_list[nserv], ai->ai_addr, ai->ai_addrlen);
|
} else {
|
statp->nsaddr_list[nserv].sin_family = AF_UNSPEC;
|
}
|
}
|
} else {
|
LOG(INFO) << __func__ << ": found too long addrlen";
|
}
|
}
|
statp->nscount = nserv;
|
// now do search domains. Note that we cache the offsets as this code runs alot
|
// but the setting/offset-computer only runs when set/changed
|
// WARNING: Don't use str*cpy() here, this string contains zeroes.
|
memcpy(statp->defdname, info->defdname, sizeof(statp->defdname));
|
char** pp = statp->dnsrch;
|
int* p = info->dnsrch_offset;
|
while (pp < statp->dnsrch + MAXDNSRCH && *p != -1) {
|
*pp++ = &statp->defdname[0] + *p++;
|
}
|
}
|
}
|
|
/* Resolver reachability statistics. */
|
|
static void _res_cache_add_stats_sample_locked(res_stats* stats, const res_sample* sample,
|
int max_samples) {
|
// Note: This function expects max_samples > 0, otherwise a (harmless) modification of the
|
// allocated but supposedly unused memory for samples[0] will happen
|
LOG(INFO) << __func__ << ": adding sample to stats, next = " << unsigned(stats->sample_next)
|
<< ", count = " << unsigned(stats->sample_count);
|
stats->samples[stats->sample_next] = *sample;
|
if (stats->sample_count < max_samples) {
|
++stats->sample_count;
|
}
|
if (++stats->sample_next >= max_samples) {
|
stats->sample_next = 0;
|
}
|
}
|
|
static void res_cache_clear_stats_locked(resolv_cache_info* cache_info) {
|
if (cache_info) {
|
for (int i = 0; i < MAXNS; ++i) {
|
cache_info->nsstats->sample_count = cache_info->nsstats->sample_next = 0;
|
}
|
}
|
}
|
|
int android_net_res_stats_get_info_for_net(unsigned netid, int* nscount,
|
struct sockaddr_storage servers[MAXNS], int* dcount,
|
char domains[MAXDNSRCH][MAXDNSRCHPATH],
|
res_params* params, struct res_stats stats[MAXNS],
|
int* wait_for_pending_req_timeout_count) {
|
int revision_id = -1;
|
std::lock_guard guard(cache_mutex);
|
|
resolv_cache_info* info = find_cache_info_locked(netid);
|
if (info) {
|
if (info->nscount > MAXNS) {
|
LOG(INFO) << __func__ << ": nscount " << info->nscount << " > MAXNS " << MAXNS;
|
errno = EFAULT;
|
return -1;
|
}
|
int i;
|
for (i = 0; i < info->nscount; i++) {
|
// Verify that the following assumptions are held, failure indicates corruption:
|
// - getaddrinfo() may never return a sockaddr > sockaddr_storage
|
// - all addresses are valid
|
// - there is only one address per addrinfo thanks to numeric resolution
|
int addrlen = info->nsaddrinfo[i]->ai_addrlen;
|
if (addrlen < (int) sizeof(struct sockaddr) || addrlen > (int) sizeof(servers[0])) {
|
LOG(INFO) << __func__ << ": nsaddrinfo[" << i << "].ai_addrlen == " << addrlen;
|
errno = EMSGSIZE;
|
return -1;
|
}
|
if (info->nsaddrinfo[i]->ai_addr == NULL) {
|
LOG(INFO) << __func__ << ": nsaddrinfo[" << i << "].ai_addr == NULL";
|
errno = ENOENT;
|
return -1;
|
}
|
if (info->nsaddrinfo[i]->ai_next != NULL) {
|
LOG(INFO) << __func__ << ": nsaddrinfo[" << i << "].ai_next != NULL";
|
errno = ENOTUNIQ;
|
return -1;
|
}
|
}
|
*nscount = info->nscount;
|
for (i = 0; i < info->nscount; i++) {
|
memcpy(&servers[i], info->nsaddrinfo[i]->ai_addr, info->nsaddrinfo[i]->ai_addrlen);
|
stats[i] = info->nsstats[i];
|
}
|
for (i = 0; i < MAXDNSRCH; i++) {
|
const char* cur_domain = info->defdname + info->dnsrch_offset[i];
|
// dnsrch_offset[i] can either be -1 or point to an empty string to indicate the end
|
// of the search offsets. Checking for < 0 is not strictly necessary, but safer.
|
// TODO: Pass in a search domain array instead of a string to
|
// resolv_set_nameservers_for_net() and make this double check unnecessary.
|
if (info->dnsrch_offset[i] < 0 ||
|
((size_t) info->dnsrch_offset[i]) >= sizeof(info->defdname) || !cur_domain[0]) {
|
break;
|
}
|
strlcpy(domains[i], cur_domain, MAXDNSRCHPATH);
|
}
|
*dcount = i;
|
*params = info->params;
|
revision_id = info->revision_id;
|
*wait_for_pending_req_timeout_count = info->wait_for_pending_req_timeout_count;
|
}
|
|
return revision_id;
|
}
|
|
int resolv_cache_get_resolver_stats(unsigned netid, res_params* params, res_stats stats[MAXNS]) {
|
std::lock_guard guard(cache_mutex);
|
resolv_cache_info* info = find_cache_info_locked(netid);
|
if (info) {
|
memcpy(stats, info->nsstats, sizeof(info->nsstats));
|
*params = info->params;
|
return info->revision_id;
|
}
|
|
return -1;
|
}
|
|
void _resolv_cache_add_resolver_stats_sample(unsigned netid, int revision_id, int ns,
|
const res_sample* sample, int max_samples) {
|
if (max_samples <= 0) return;
|
|
std::lock_guard guard(cache_mutex);
|
resolv_cache_info* info = find_cache_info_locked(netid);
|
|
if (info && info->revision_id == revision_id) {
|
_res_cache_add_stats_sample_locked(&info->nsstats[ns], sample, max_samples);
|
}
|
}
|
