/*
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* Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.com>
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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// Test that /proc/$KERNEL_THREAD/fd/ is empty.
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#undef NDEBUG
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#include <sys/syscall.h>
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#include <assert.h>
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#include <dirent.h>
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#include <limits.h>
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#include <stdio.h>
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#include <string.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <unistd.h>
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#include "proc.h"
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#define PF_KHTREAD 0x00200000
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/*
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* Test for kernel threadness atomically with openat().
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*
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* Return /proc/$PID/fd descriptor if process is kernel thread.
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* Return -1 if a process is userspace process.
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*/
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static int kernel_thread_fd(unsigned int pid)
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{
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unsigned int flags = 0;
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char buf[4096];
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int dir_fd, fd;
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ssize_t rv;
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snprintf(buf, sizeof(buf), "/proc/%u", pid);
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dir_fd = open(buf, O_RDONLY|O_DIRECTORY);
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if (dir_fd == -1)
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return -1;
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/*
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* Believe it or not, struct task_struct::flags is directly exposed
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* to userspace!
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*/
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fd = openat(dir_fd, "stat", O_RDONLY);
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if (fd == -1) {
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close(dir_fd);
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return -1;
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}
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rv = read(fd, buf, sizeof(buf));
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close(fd);
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if (0 < rv && rv <= sizeof(buf)) {
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unsigned long long flags_ull;
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char *p, *end;
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int i;
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assert(buf[rv - 1] == '\n');
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buf[rv - 1] = '\0';
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/* Search backwards: ->comm can contain whitespace and ')'. */
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for (i = 0; i < 43; i++) {
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p = strrchr(buf, ' ');
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assert(p);
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*p = '\0';
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}
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p = strrchr(buf, ' ');
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assert(p);
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flags_ull = xstrtoull(p + 1, &end);
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assert(*end == '\0');
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assert(flags_ull == (unsigned int)flags_ull);
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flags = flags_ull;
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}
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fd = -1;
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if (flags & PF_KHTREAD) {
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fd = openat(dir_fd, "fd", O_RDONLY|O_DIRECTORY);
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}
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close(dir_fd);
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return fd;
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}
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static void test_readdir(int fd)
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{
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DIR *d;
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struct dirent *de;
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d = fdopendir(fd);
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assert(d);
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de = xreaddir(d);
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assert(streq(de->d_name, "."));
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assert(de->d_type == DT_DIR);
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de = xreaddir(d);
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assert(streq(de->d_name, ".."));
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assert(de->d_type == DT_DIR);
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de = xreaddir(d);
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assert(!de);
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}
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static inline int sys_statx(int dirfd, const char *pathname, int flags,
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unsigned int mask, void *stx)
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{
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return syscall(SYS_statx, dirfd, pathname, flags, mask, stx);
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}
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static void test_lookup_fail(int fd, const char *pathname)
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{
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char stx[256] __attribute__((aligned(8)));
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int rv;
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rv = sys_statx(fd, pathname, AT_SYMLINK_NOFOLLOW, 0, (void *)stx);
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assert(rv == -1 && errno == ENOENT);
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}
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static void test_lookup(int fd)
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{
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char buf[64];
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unsigned int u;
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int i;
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for (i = INT_MIN; i < INT_MIN + 1024; i++) {
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snprintf(buf, sizeof(buf), "%d", i);
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test_lookup_fail(fd, buf);
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}
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for (i = -1024; i < 1024; i++) {
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snprintf(buf, sizeof(buf), "%d", i);
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test_lookup_fail(fd, buf);
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}
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for (u = INT_MAX - 1024; u < (unsigned int)INT_MAX + 1024; u++) {
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snprintf(buf, sizeof(buf), "%u", u);
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test_lookup_fail(fd, buf);
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}
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for (u = UINT_MAX - 1024; u != 0; u++) {
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snprintf(buf, sizeof(buf), "%u", u);
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test_lookup_fail(fd, buf);
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}
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}
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int main(void)
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{
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unsigned int pid;
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int fd;
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/*
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* In theory this will loop indefinitely if kernel threads are exiled
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* from /proc.
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*
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* Start with kthreadd.
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*/
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pid = 2;
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while ((fd = kernel_thread_fd(pid)) == -1 && pid < 1024) {
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pid++;
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}
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/* EACCES if run as non-root. */
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if (pid >= 1024)
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return 1;
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test_readdir(fd);
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test_lookup(fd);
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return 0;
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}
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