LXR linux/tools/testing/selftests/proc/fd-003-kthread.c

   1/*
   2 * Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.com>
   3 *
   4 * Permission to use, copy, modify, and distribute this software for any
   5 * purpose with or without fee is hereby granted, provided that the above
   6 * copyright notice and this permission notice appear in all copies.
   7 *
   8 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
   9 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  10 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  11 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  12 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  13 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  14 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  15 */
  16// Test that /proc/$KERNEL_THREAD/fd/ is empty.
  17
  18#undef NDEBUG
  19#include <sys/syscall.h>
  20#include <assert.h>
  21#include <dirent.h>
  22#include <limits.h>
  23#include <stdio.h>
  24#include <string.h>
  25#include <sys/types.h>
  26#include <sys/stat.h>
  27#include <fcntl.h>
  28#include <unistd.h>
  29
  30#include "proc.h"
  31
  32#define PF_KHTREAD 0x00200000
  33
  34/*
  35 * Test for kernel threadness atomically with openat().
  36 *
  37 * Return /proc/$PID/fd descriptor if process is kernel thread.
  38 * Return -1 if a process is userspace process.
  39 */
  40static int kernel_thread_fd(unsigned int pid)
  41{
  42        unsigned int flags = 0;
  43        char buf[4096];
  44        int dir_fd, fd;
  45        ssize_t rv;
  46
  47        snprintf(buf, sizeof(buf), "/proc/%u", pid);
  48        dir_fd = open(buf, O_RDONLY|O_DIRECTORY);
  49        if (dir_fd == -1)
  50                return -1;
  51
  52        /*
  53         * Believe it or not, struct task_struct::flags is directly exposed
  54         * to userspace!
  55         */
  56        fd = openat(dir_fd, "stat", O_RDONLY);
  57        if (fd == -1) {
  58                close(dir_fd);
  59                return -1;
  60        }
  61        rv = read(fd, buf, sizeof(buf));
  62        close(fd);
  63        if (0 < rv && rv <= sizeof(buf)) {
  64                unsigned long long flags_ull;
  65                char *p, *end;
  66                int i;
  67
  68                assert(buf[rv - 1] == '\n');
  69                buf[rv - 1] = '\0';
  70
  71                /* Search backwards: ->comm can contain whitespace and ')'. */
  72                for (i = 0; i < 43; i++) {
  73                        p = strrchr(buf, ' ');
  74                        assert(p);
  75                        *p = '\0';
  76                }
  77
  78                p = strrchr(buf, ' ');
  79                assert(p);
  80
  81                flags_ull = xstrtoull(p + 1, &end);
  82                assert(*end == '\0');
  83                assert(flags_ull == (unsigned int)flags_ull);
  84
  85                flags = flags_ull;
  86        }
  87
  88        fd = -1;
  89        if (flags & PF_KHTREAD) {
  90                fd = openat(dir_fd, "fd", O_RDONLY|O_DIRECTORY);
  91        }
  92        close(dir_fd);
  93        return fd;
  94}
  95
  96static void test_readdir(int fd)
  97{
  98        DIR *d;
  99        struct dirent *de;
 100
 101        d = fdopendir(fd);
 102        assert(d);
 103
 104        de = xreaddir(d);
 105        assert(streq(de->d_name, "."));
 106        assert(de->d_type == DT_DIR);
 107
 108        de = xreaddir(d);
 109        assert(streq(de->d_name, ".."));
 110        assert(de->d_type == DT_DIR);
 111
 112        de = xreaddir(d);
 113        assert(!de);
 114}
 115
 116static inline int sys_statx(int dirfd, const char *pathname, int flags,
 117                            unsigned int mask, void *stx)
 118{
 119        return syscall(SYS_statx, dirfd, pathname, flags, mask, stx);
 120}
 121
 122static void test_lookup_fail(int fd, const char *pathname)
 123{
 124        char stx[256] __attribute__((aligned(8)));
 125        int rv;
 126
 127        rv = sys_statx(fd, pathname, AT_SYMLINK_NOFOLLOW, 0, (void *)stx);
 128        assert(rv == -1 && errno == ENOENT);
 129}
 130
 131static void test_lookup(int fd)
 132{
 133        char buf[64];
 134        unsigned int u;
 135        int i;
 136
 137        for (i = INT_MIN; i < INT_MIN + 1024; i++) {
 138                snprintf(buf, sizeof(buf), "%d", i);
 139                test_lookup_fail(fd, buf);
 140        }
 141        for (i = -1024; i < 1024; i++) {
 142                snprintf(buf, sizeof(buf), "%d", i);
 143                test_lookup_fail(fd, buf);
 144        }
 145        for (u = INT_MAX - 1024; u < (unsigned int)INT_MAX + 1024; u++) {
 146                snprintf(buf, sizeof(buf), "%u", u);
 147                test_lookup_fail(fd, buf);
 148        }
 149        for (u = UINT_MAX - 1024; u != 0; u++) {
 150                snprintf(buf, sizeof(buf), "%u", u);
 151                test_lookup_fail(fd, buf);
 152        }
 153}
 154
 155int main(void)
 156{
 157        unsigned int pid;
 158        int fd;
 159
 160        /*
 161         * In theory this will loop indefinitely if kernel threads are exiled
 162         * from /proc.
 163         *
 164         * Start with kthreadd.
 165         */
 166        pid = 2;
 167        while ((fd = kernel_thread_fd(pid)) == -1 && pid < 1024) {
 168                pid++;
 169        }
 170        /* EACCES if run as non-root. */
 171        if (pid >= 1024)
 172                return 1;
 173
 174        test_readdir(fd);
 175        test_lookup(fd);
 176
 177        return 0;
 178}
 179