// SPDX-License-Identifier: GPL-2.0-only
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/* FTP extension for connection tracking. */
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/* (C) 1999-2001 Paul `Rusty' Russell
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* (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
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* (C) 2003,2004 USAGI/WIDE Project <http://www.linux-ipv6.org>
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* (C) 2006-2012 Patrick McHardy <kaber@trash.net>
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/module.h>
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#include <linux/moduleparam.h>
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#include <linux/netfilter.h>
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#include <linux/ip.h>
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#include <linux/slab.h>
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#include <linux/ipv6.h>
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#include <linux/ctype.h>
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#include <linux/inet.h>
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#include <net/checksum.h>
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#include <net/tcp.h>
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#include <net/netfilter/nf_conntrack.h>
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#include <net/netfilter/nf_conntrack_expect.h>
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#include <net/netfilter/nf_conntrack_ecache.h>
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#include <net/netfilter/nf_conntrack_helper.h>
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#include <linux/netfilter/nf_conntrack_ftp.h>
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#define HELPER_NAME "ftp"
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MODULE_LICENSE("GPL");
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MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
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MODULE_DESCRIPTION("ftp connection tracking helper");
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MODULE_ALIAS("ip_conntrack_ftp");
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MODULE_ALIAS_NFCT_HELPER(HELPER_NAME);
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/* This is slow, but it's simple. --RR */
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static char *ftp_buffer;
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static DEFINE_SPINLOCK(nf_ftp_lock);
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#define MAX_PORTS 8
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static u_int16_t ports[MAX_PORTS];
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static unsigned int ports_c;
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module_param_array(ports, ushort, &ports_c, 0400);
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static bool loose;
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module_param(loose, bool, 0600);
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unsigned int (*nf_nat_ftp_hook)(struct sk_buff *skb,
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enum ip_conntrack_info ctinfo,
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enum nf_ct_ftp_type type,
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unsigned int protoff,
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unsigned int matchoff,
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unsigned int matchlen,
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struct nf_conntrack_expect *exp);
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EXPORT_SYMBOL_GPL(nf_nat_ftp_hook);
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static int try_rfc959(const char *, size_t, struct nf_conntrack_man *,
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char, unsigned int *);
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static int try_rfc1123(const char *, size_t, struct nf_conntrack_man *,
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char, unsigned int *);
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static int try_eprt(const char *, size_t, struct nf_conntrack_man *,
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char, unsigned int *);
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static int try_epsv_response(const char *, size_t, struct nf_conntrack_man *,
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char, unsigned int *);
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static struct ftp_search {
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const char *pattern;
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size_t plen;
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char skip;
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char term;
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enum nf_ct_ftp_type ftptype;
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int (*getnum)(const char *, size_t, struct nf_conntrack_man *, char, unsigned int *);
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} search[IP_CT_DIR_MAX][2] = {
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[IP_CT_DIR_ORIGINAL] = {
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{
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.pattern = "PORT",
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.plen = sizeof("PORT") - 1,
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.skip = ' ',
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.term = '\r',
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.ftptype = NF_CT_FTP_PORT,
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.getnum = try_rfc959,
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},
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{
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.pattern = "EPRT",
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.plen = sizeof("EPRT") - 1,
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.skip = ' ',
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.term = '\r',
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.ftptype = NF_CT_FTP_EPRT,
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.getnum = try_eprt,
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},
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},
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[IP_CT_DIR_REPLY] = {
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{
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.pattern = "227 ",
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.plen = sizeof("227 ") - 1,
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.ftptype = NF_CT_FTP_PASV,
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.getnum = try_rfc1123,
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},
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{
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.pattern = "229 ",
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.plen = sizeof("229 ") - 1,
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.skip = '(',
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.term = ')',
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.ftptype = NF_CT_FTP_EPSV,
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.getnum = try_epsv_response,
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},
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},
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};
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static int
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get_ipv6_addr(const char *src, size_t dlen, struct in6_addr *dst, u_int8_t term)
|
{
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const char *end;
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int ret = in6_pton(src, min_t(size_t, dlen, 0xffff), (u8 *)dst, term, &end);
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if (ret > 0)
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return (int)(end - src);
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return 0;
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}
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static int try_number(const char *data, size_t dlen, u_int32_t array[],
|
int array_size, char sep, char term)
|
{
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u_int32_t i, len;
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memset(array, 0, sizeof(array[0])*array_size);
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/* Keep data pointing at next char. */
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for (i = 0, len = 0; len < dlen && i < array_size; len++, data++) {
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if (*data >= '0' && *data <= '9') {
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array[i] = array[i]*10 + *data - '0';
|
}
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else if (*data == sep)
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i++;
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else {
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/* Unexpected character; true if it's the
|
terminator (or we don't care about one)
|
and we're finished. */
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if ((*data == term || !term) && i == array_size - 1)
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return len;
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pr_debug("Char %u (got %u nums) `%u' unexpected\n",
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len, i, *data);
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return 0;
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}
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}
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pr_debug("Failed to fill %u numbers separated by %c\n",
|
array_size, sep);
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return 0;
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}
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/* Returns 0, or length of numbers: 192,168,1,1,5,6 */
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static int try_rfc959(const char *data, size_t dlen,
|
struct nf_conntrack_man *cmd, char term,
|
unsigned int *offset)
|
{
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int length;
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u_int32_t array[6];
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length = try_number(data, dlen, array, 6, ',', term);
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if (length == 0)
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return 0;
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cmd->u3.ip = htonl((array[0] << 24) | (array[1] << 16) |
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(array[2] << 8) | array[3]);
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cmd->u.tcp.port = htons((array[4] << 8) | array[5]);
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return length;
|
}
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|
/*
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* From RFC 1123:
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* The format of the 227 reply to a PASV command is not
|
* well standardized. In particular, an FTP client cannot
|
* assume that the parentheses shown on page 40 of RFC-959
|
* will be present (and in fact, Figure 3 on page 43 omits
|
* them). Therefore, a User-FTP program that interprets
|
* the PASV reply must scan the reply for the first digit
|
* of the host and port numbers.
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*/
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static int try_rfc1123(const char *data, size_t dlen,
|
struct nf_conntrack_man *cmd, char term,
|
unsigned int *offset)
|
{
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int i;
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for (i = 0; i < dlen; i++)
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if (isdigit(data[i]))
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break;
|
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if (i == dlen)
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return 0;
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*offset += i;
|
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return try_rfc959(data + i, dlen - i, cmd, 0, offset);
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}
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/* Grab port: number up to delimiter */
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static int get_port(const char *data, int start, size_t dlen, char delim,
|
__be16 *port)
|
{
|
u_int16_t tmp_port = 0;
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int i;
|
|
for (i = start; i < dlen; i++) {
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/* Finished? */
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if (data[i] == delim) {
|
if (tmp_port == 0)
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break;
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*port = htons(tmp_port);
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pr_debug("get_port: return %d\n", tmp_port);
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return i + 1;
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}
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else if (data[i] >= '0' && data[i] <= '9')
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tmp_port = tmp_port*10 + data[i] - '0';
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else { /* Some other crap */
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pr_debug("get_port: invalid char.\n");
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break;
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}
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}
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return 0;
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}
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/* Returns 0, or length of numbers: |1|132.235.1.2|6275| or |2|3ffe::1|6275| */
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static int try_eprt(const char *data, size_t dlen, struct nf_conntrack_man *cmd,
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char term, unsigned int *offset)
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{
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char delim;
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int length;
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/* First character is delimiter, then "1" for IPv4 or "2" for IPv6,
|
then delimiter again. */
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if (dlen <= 3) {
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pr_debug("EPRT: too short\n");
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return 0;
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}
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delim = data[0];
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if (isdigit(delim) || delim < 33 || delim > 126 || data[2] != delim) {
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pr_debug("try_eprt: invalid delimiter.\n");
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return 0;
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}
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if ((cmd->l3num == PF_INET && data[1] != '1') ||
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(cmd->l3num == PF_INET6 && data[1] != '2')) {
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pr_debug("EPRT: invalid protocol number.\n");
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return 0;
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}
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pr_debug("EPRT: Got %c%c%c\n", delim, data[1], delim);
|
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if (data[1] == '1') {
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u_int32_t array[4];
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/* Now we have IP address. */
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length = try_number(data + 3, dlen - 3, array, 4, '.', delim);
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if (length != 0)
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cmd->u3.ip = htonl((array[0] << 24) | (array[1] << 16)
|
| (array[2] << 8) | array[3]);
|
} else {
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/* Now we have IPv6 address. */
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length = get_ipv6_addr(data + 3, dlen - 3,
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(struct in6_addr *)cmd->u3.ip6, delim);
|
}
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if (length == 0)
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return 0;
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pr_debug("EPRT: Got IP address!\n");
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/* Start offset includes initial "|1|", and trailing delimiter */
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return get_port(data, 3 + length + 1, dlen, delim, &cmd->u.tcp.port);
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}
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/* Returns 0, or length of numbers: |||6446| */
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static int try_epsv_response(const char *data, size_t dlen,
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struct nf_conntrack_man *cmd, char term,
|
unsigned int *offset)
|
{
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char delim;
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/* Three delimiters. */
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if (dlen <= 3) return 0;
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delim = data[0];
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if (isdigit(delim) || delim < 33 || delim > 126 ||
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data[1] != delim || data[2] != delim)
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return 0;
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return get_port(data, 3, dlen, delim, &cmd->u.tcp.port);
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}
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/* Return 1 for match, 0 for accept, -1 for partial. */
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static int find_pattern(const char *data, size_t dlen,
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const char *pattern, size_t plen,
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char skip, char term,
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unsigned int *numoff,
|
unsigned int *numlen,
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struct nf_conntrack_man *cmd,
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int (*getnum)(const char *, size_t,
|
struct nf_conntrack_man *, char,
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unsigned int *))
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{
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size_t i = plen;
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pr_debug("find_pattern `%s': dlen = %zu\n", pattern, dlen);
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if (dlen <= plen) {
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/* Short packet: try for partial? */
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if (strncasecmp(data, pattern, dlen) == 0)
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return -1;
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else return 0;
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}
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if (strncasecmp(data, pattern, plen) != 0)
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return 0;
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pr_debug("Pattern matches!\n");
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/* Now we've found the constant string, try to skip
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to the 'skip' character */
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if (skip) {
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for (i = plen; data[i] != skip; i++)
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if (i == dlen - 1) return -1;
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/* Skip over the last character */
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i++;
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}
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pr_debug("Skipped up to 0x%hhx delimiter!\n", skip);
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*numoff = i;
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*numlen = getnum(data + i, dlen - i, cmd, term, numoff);
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if (!*numlen)
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return -1;
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pr_debug("Match succeeded!\n");
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return 1;
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}
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/* Look up to see if we're just after a \n. */
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static int find_nl_seq(u32 seq, const struct nf_ct_ftp_master *info, int dir)
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{
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unsigned int i;
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for (i = 0; i < info->seq_aft_nl_num[dir]; i++)
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if (info->seq_aft_nl[dir][i] == seq)
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return 1;
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return 0;
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}
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/* We don't update if it's older than what we have. */
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static void update_nl_seq(struct nf_conn *ct, u32 nl_seq,
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struct nf_ct_ftp_master *info, int dir,
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struct sk_buff *skb)
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{
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unsigned int i, oldest;
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/* Look for oldest: if we find exact match, we're done. */
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for (i = 0; i < info->seq_aft_nl_num[dir]; i++) {
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if (info->seq_aft_nl[dir][i] == nl_seq)
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return;
|
}
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if (info->seq_aft_nl_num[dir] < NUM_SEQ_TO_REMEMBER) {
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info->seq_aft_nl[dir][info->seq_aft_nl_num[dir]++] = nl_seq;
|
} else {
|
if (before(info->seq_aft_nl[dir][0], info->seq_aft_nl[dir][1]))
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oldest = 0;
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else
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oldest = 1;
|
|
if (after(nl_seq, info->seq_aft_nl[dir][oldest]))
|
info->seq_aft_nl[dir][oldest] = nl_seq;
|
}
|
}
|
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static int help(struct sk_buff *skb,
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unsigned int protoff,
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struct nf_conn *ct,
|
enum ip_conntrack_info ctinfo)
|
{
|
unsigned int dataoff, datalen;
|
const struct tcphdr *th;
|
struct tcphdr _tcph;
|
const char *fb_ptr;
|
int ret;
|
u32 seq;
|
int dir = CTINFO2DIR(ctinfo);
|
unsigned int matchlen, matchoff;
|
struct nf_ct_ftp_master *ct_ftp_info = nfct_help_data(ct);
|
struct nf_conntrack_expect *exp;
|
union nf_inet_addr *daddr;
|
struct nf_conntrack_man cmd = {};
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unsigned int i;
|
int found = 0, ends_in_nl;
|
typeof(nf_nat_ftp_hook) nf_nat_ftp;
|
|
/* Until there's been traffic both ways, don't look in packets. */
|
if (ctinfo != IP_CT_ESTABLISHED &&
|
ctinfo != IP_CT_ESTABLISHED_REPLY) {
|
pr_debug("ftp: Conntrackinfo = %u\n", ctinfo);
|
return NF_ACCEPT;
|
}
|
|
th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
|
if (th == NULL)
|
return NF_ACCEPT;
|
|
dataoff = protoff + th->doff * 4;
|
/* No data? */
|
if (dataoff >= skb->len) {
|
pr_debug("ftp: dataoff(%u) >= skblen(%u)\n", dataoff,
|
skb->len);
|
return NF_ACCEPT;
|
}
|
datalen = skb->len - dataoff;
|
|
spin_lock_bh(&nf_ftp_lock);
|
fb_ptr = skb_header_pointer(skb, dataoff, datalen, ftp_buffer);
|
BUG_ON(fb_ptr == NULL);
|
|
ends_in_nl = (fb_ptr[datalen - 1] == '\n');
|
seq = ntohl(th->seq) + datalen;
|
|
/* Look up to see if we're just after a \n. */
|
if (!find_nl_seq(ntohl(th->seq), ct_ftp_info, dir)) {
|
/* We're picking up this, clear flags and let it continue */
|
if (unlikely(ct_ftp_info->flags[dir] & NF_CT_FTP_SEQ_PICKUP)) {
|
ct_ftp_info->flags[dir] ^= NF_CT_FTP_SEQ_PICKUP;
|
goto skip_nl_seq;
|
}
|
|
/* Now if this ends in \n, update ftp info. */
|
pr_debug("nf_conntrack_ftp: wrong seq pos %s(%u) or %s(%u)\n",
|
ct_ftp_info->seq_aft_nl_num[dir] > 0 ? "" : "(UNSET)",
|
ct_ftp_info->seq_aft_nl[dir][0],
|
ct_ftp_info->seq_aft_nl_num[dir] > 1 ? "" : "(UNSET)",
|
ct_ftp_info->seq_aft_nl[dir][1]);
|
ret = NF_ACCEPT;
|
goto out_update_nl;
|
}
|
|
skip_nl_seq:
|
/* Initialize IP/IPv6 addr to expected address (it's not mentioned
|
in EPSV responses) */
|
cmd.l3num = nf_ct_l3num(ct);
|
memcpy(cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all,
|
sizeof(cmd.u3.all));
|
|
for (i = 0; i < ARRAY_SIZE(search[dir]); i++) {
|
found = find_pattern(fb_ptr, datalen,
|
search[dir][i].pattern,
|
search[dir][i].plen,
|
search[dir][i].skip,
|
search[dir][i].term,
|
&matchoff, &matchlen,
|
&cmd,
|
search[dir][i].getnum);
|
if (found) break;
|
}
|
if (found == -1) {
|
/* We don't usually drop packets. After all, this is
|
connection tracking, not packet filtering.
|
However, it is necessary for accurate tracking in
|
this case. */
|
nf_ct_helper_log(skb, ct, "partial matching of `%s'",
|
search[dir][i].pattern);
|
ret = NF_DROP;
|
goto out;
|
} else if (found == 0) { /* No match */
|
ret = NF_ACCEPT;
|
goto out_update_nl;
|
}
|
|
pr_debug("conntrack_ftp: match `%.*s' (%u bytes at %u)\n",
|
matchlen, fb_ptr + matchoff,
|
matchlen, ntohl(th->seq) + matchoff);
|
|
exp = nf_ct_expect_alloc(ct);
|
if (exp == NULL) {
|
nf_ct_helper_log(skb, ct, "cannot alloc expectation");
|
ret = NF_DROP;
|
goto out;
|
}
|
|
/* We refer to the reverse direction ("!dir") tuples here,
|
* because we're expecting something in the other direction.
|
* Doesn't matter unless NAT is happening. */
|
daddr = &ct->tuplehash[!dir].tuple.dst.u3;
|
|
/* Update the ftp info */
|
if ((cmd.l3num == nf_ct_l3num(ct)) &&
|
memcmp(&cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all,
|
sizeof(cmd.u3.all))) {
|
/* Enrico Scholz's passive FTP to partially RNAT'd ftp
|
server: it really wants us to connect to a
|
different IP address. Simply don't record it for
|
NAT. */
|
if (cmd.l3num == PF_INET) {
|
pr_debug("NOT RECORDING: %pI4 != %pI4\n",
|
&cmd.u3.ip,
|
&ct->tuplehash[dir].tuple.src.u3.ip);
|
} else {
|
pr_debug("NOT RECORDING: %pI6 != %pI6\n",
|
cmd.u3.ip6,
|
ct->tuplehash[dir].tuple.src.u3.ip6);
|
}
|
|
/* Thanks to Cristiano Lincoln Mattos
|
<lincoln@cesar.org.br> for reporting this potential
|
problem (DMZ machines opening holes to internal
|
networks, or the packet filter itself). */
|
if (!loose) {
|
ret = NF_ACCEPT;
|
goto out_put_expect;
|
}
|
daddr = &cmd.u3;
|
}
|
|
nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, cmd.l3num,
|
&ct->tuplehash[!dir].tuple.src.u3, daddr,
|
IPPROTO_TCP, NULL, &cmd.u.tcp.port);
|
|
/* Now, NAT might want to mangle the packet, and register the
|
* (possibly changed) expectation itself. */
|
nf_nat_ftp = rcu_dereference(nf_nat_ftp_hook);
|
if (nf_nat_ftp && ct->status & IPS_NAT_MASK)
|
ret = nf_nat_ftp(skb, ctinfo, search[dir][i].ftptype,
|
protoff, matchoff, matchlen, exp);
|
else {
|
/* Can't expect this? Best to drop packet now. */
|
if (nf_ct_expect_related(exp, 0) != 0) {
|
nf_ct_helper_log(skb, ct, "cannot add expectation");
|
ret = NF_DROP;
|
} else
|
ret = NF_ACCEPT;
|
}
|
|
out_put_expect:
|
nf_ct_expect_put(exp);
|
|
out_update_nl:
|
/* Now if this ends in \n, update ftp info. Seq may have been
|
* adjusted by NAT code. */
|
if (ends_in_nl)
|
update_nl_seq(ct, seq, ct_ftp_info, dir, skb);
|
out:
|
spin_unlock_bh(&nf_ftp_lock);
|
return ret;
|
}
|
|
static int nf_ct_ftp_from_nlattr(struct nlattr *attr, struct nf_conn *ct)
|
{
|
struct nf_ct_ftp_master *ftp = nfct_help_data(ct);
|
|
/* This conntrack has been injected from user-space, always pick up
|
* sequence tracking. Otherwise, the first FTP command after the
|
* failover breaks.
|
*/
|
ftp->flags[IP_CT_DIR_ORIGINAL] |= NF_CT_FTP_SEQ_PICKUP;
|
ftp->flags[IP_CT_DIR_REPLY] |= NF_CT_FTP_SEQ_PICKUP;
|
return 0;
|
}
|
|
static struct nf_conntrack_helper ftp[MAX_PORTS * 2] __read_mostly;
|
|
static const struct nf_conntrack_expect_policy ftp_exp_policy = {
|
.max_expected = 1,
|
.timeout = 5 * 60,
|
};
|
|
static void __exit nf_conntrack_ftp_fini(void)
|
{
|
nf_conntrack_helpers_unregister(ftp, ports_c * 2);
|
kfree(ftp_buffer);
|
}
|
|
static int __init nf_conntrack_ftp_init(void)
|
{
|
int i, ret = 0;
|
|
NF_CT_HELPER_BUILD_BUG_ON(sizeof(struct nf_ct_ftp_master));
|
|
ftp_buffer = kmalloc(65536, GFP_KERNEL);
|
if (!ftp_buffer)
|
return -ENOMEM;
|
|
if (ports_c == 0)
|
ports[ports_c++] = FTP_PORT;
|
|
/* FIXME should be configurable whether IPv4 and IPv6 FTP connections
|
are tracked or not - YK */
|
for (i = 0; i < ports_c; i++) {
|
nf_ct_helper_init(&ftp[2 * i], AF_INET, IPPROTO_TCP,
|
HELPER_NAME, FTP_PORT, ports[i], ports[i],
|
&ftp_exp_policy, 0, help,
|
nf_ct_ftp_from_nlattr, THIS_MODULE);
|
nf_ct_helper_init(&ftp[2 * i + 1], AF_INET6, IPPROTO_TCP,
|
HELPER_NAME, FTP_PORT, ports[i], ports[i],
|
&ftp_exp_policy, 0, help,
|
nf_ct_ftp_from_nlattr, THIS_MODULE);
|
}
|
|
ret = nf_conntrack_helpers_register(ftp, ports_c * 2);
|
if (ret < 0) {
|
pr_err("failed to register helpers\n");
|
kfree(ftp_buffer);
|
return ret;
|
}
|
|
return 0;
|
}
|
|
module_init(nf_conntrack_ftp_init);
|
module_exit(nf_conntrack_ftp_fini);
|
