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178 lines
3.9 KiB
178 lines
3.9 KiB
/* |
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* Copyright © 2018 Alexey Dobriyan <[email protected]> |
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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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