tools/testing/selftests/mount/nosymfollow-test.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #define _GNU_SOURCE
   3 #include <errno.h>
   4 #include <fcntl.h>
   5 #include <limits.h>
   6 #include <sched.h>
   7 #include <stdarg.h>
   8 #include <stdbool.h>
   9 #include <stdio.h>
  10 #include <stdlib.h>
  11 #include <string.h>
  12 #include <sys/mount.h>
  13 #include <sys/stat.h>
  14 #include <sys/types.h>
  15 #include <sys/vfs.h>
  16 #include <unistd.h>
  17
  18 #ifndef MS_NOSYMFOLLOW
  19 # define MS_NOSYMFOLLOW 256     /* Do not follow symlinks */
  20 #endif
  21
  22 #ifndef ST_NOSYMFOLLOW
  23 # define ST_NOSYMFOLLOW 0x2000  /* Do not follow symlinks */
  24 #endif
  25
  26 #define DATA "/tmp/data"
  27 #define LINK "/tmp/symlink"
  28 #define TMP  "/tmp"
  29
  30 static void die(char *fmt, ...)
  31 {
  32         va_list ap;
  33
  34         va_start(ap, fmt);
  35         vfprintf(stderr, fmt, ap);
  36         va_end(ap);
  37         exit(EXIT_FAILURE);
  38 }
  39
  40 static void vmaybe_write_file(bool enoent_ok, char *filename, char *fmt,
  41                 va_list ap)
  42 {
  43         ssize_t written;
  44         char buf[4096];
  45         int buf_len;
  46         int fd;
  47
  48         buf_len = vsnprintf(buf, sizeof(buf), fmt, ap);
  49         if (buf_len < 0)
  50                 die("vsnprintf failed: %s\n", strerror(errno));
  51
  52         if (buf_len >= sizeof(buf))
  53                 die("vsnprintf output truncated\n");
  54
  55         fd = open(filename, O_WRONLY);
  56         if (fd < 0) {
  57                 if ((errno == ENOENT) && enoent_ok)
  58                         return;
  59                 die("open of %s failed: %s\n", filename, strerror(errno));
  60         }
  61
  62         written = write(fd, buf, buf_len);
  63         if (written != buf_len) {
  64                 if (written >= 0) {
  65                         die("short write to %s\n", filename);
  66                 } else {
  67                         die("write to %s failed: %s\n",
  68                                 filename, strerror(errno));
  69                 }
  70         }
  71
  72         if (close(fd) != 0)
  73                 die("close of %s failed: %s\n", filename, strerror(errno));
  74 }
  75
  76 static void maybe_write_file(char *filename, char *fmt, ...)
  77 {
  78         va_list ap;
  79
  80         va_start(ap, fmt);
  81         vmaybe_write_file(true, filename, fmt, ap);
  82         va_end(ap);
  83 }
  84
  85 static void write_file(char *filename, char *fmt, ...)
  86 {
  87         va_list ap;
  88
  89         va_start(ap, fmt);
  90         vmaybe_write_file(false, filename, fmt, ap);
  91         va_end(ap);
  92 }
  93
  94 static void create_and_enter_ns(void)
  95 {
  96         uid_t uid = getuid();
  97         gid_t gid = getgid();
  98
  99         if (unshare(CLONE_NEWUSER) != 0)
 100                 die("unshare(CLONE_NEWUSER) failed: %s\n", strerror(errno));
 101
 102         maybe_write_file("/proc/self/setgroups", "deny");
 103         write_file("/proc/self/uid_map", "0 %d 1", uid);
 104         write_file("/proc/self/gid_map", "0 %d 1", gid);
 105
 106         if (setgid(0) != 0)
 107                 die("setgid(0) failed %s\n", strerror(errno));
 108         if (setuid(0) != 0)
 109                 die("setuid(0) failed %s\n", strerror(errno));
 110
 111         if (unshare(CLONE_NEWNS) != 0)
 112                 die("unshare(CLONE_NEWNS) failed: %s\n", strerror(errno));
 113 }
 114
 115 static void setup_symlink(void)
 116 {
 117         int data, err;
 118
 119         data = creat(DATA, O_RDWR);
 120         if (data < 0)
 121                 die("creat failed: %s\n", strerror(errno));
 122
 123         err = symlink(DATA, LINK);
 124         if (err < 0)
 125                 die("symlink failed: %s\n", strerror(errno));
 126
 127         if (close(data) != 0)
 128                 die("close of %s failed: %s\n", DATA, strerror(errno));
 129 }
 130
 131 static void test_link_traversal(bool nosymfollow)
 132 {
 133         int link;
 134
 135         link = open(LINK, 0, O_RDWR);
 136         if (nosymfollow) {
 137                 if ((link != -1 || errno != ELOOP)) {
 138                         die("link traversal unexpected result: %d, %s\n",
 139                                         link, strerror(errno));
 140                 }
 141         } else {
 142                 if (link < 0)
 143                         die("link traversal failed: %s\n", strerror(errno));
 144
 145                 if (close(link) != 0)
 146                         die("close of link failed: %s\n", strerror(errno));
 147         }
 148 }
 149
 150 static void test_readlink(void)
 151 {
 152         char buf[4096];
 153         ssize_t ret;
 154
 155         bzero(buf, sizeof(buf));
 156
 157         ret = readlink(LINK, buf, sizeof(buf));
 158         if (ret < 0)
 159                 die("readlink failed: %s\n", strerror(errno));
 160         if (strcmp(buf, DATA) != 0)
 161                 die("readlink strcmp failed: '%s' '%s'\n", buf, DATA);
 162 }
 163
 164 static void test_realpath(void)
 165 {
 166         char *path = realpath(LINK, NULL);
 167
 168         if (!path)
 169                 die("realpath failed: %s\n", strerror(errno));
 170         if (strcmp(path, DATA) != 0)
 171                 die("realpath strcmp failed\n");
 172
 173         free(path);
 174 }
 175
 176 static void test_statfs(bool nosymfollow)
 177 {
 178         struct statfs buf;
 179         int ret;
 180
 181         ret = statfs(TMP, &buf);
 182         if (ret)
 183                 die("statfs failed: %s\n", strerror(errno));
 184
 185         if (nosymfollow) {
 186                 if ((buf.f_flags & ST_NOSYMFOLLOW) == 0)
 187                         die("ST_NOSYMFOLLOW not set on %s\n", TMP);
 188         } else {
 189                 if ((buf.f_flags & ST_NOSYMFOLLOW) != 0)
 190                         die("ST_NOSYMFOLLOW set on %s\n", TMP);
 191         }
 192 }
 193
 194 static void run_tests(bool nosymfollow)
 195 {
 196         test_link_traversal(nosymfollow);
 197         test_readlink();
 198         test_realpath();
 199         test_statfs(nosymfollow);
 200 }
 201
 202 int main(int argc, char **argv)
 203 {
 204         create_and_enter_ns();
 205
 206         if (mount("testing", TMP, "ramfs", 0, NULL) != 0)
 207                 die("mount failed: %s\n", strerror(errno));
 208
 209         setup_symlink();
 210         run_tests(false);
 211
 212         if (mount("testing", TMP, "ramfs", MS_REMOUNT|MS_NOSYMFOLLOW, NULL) != 0)
 213                 die("remount failed: %s\n", strerror(errno));
 214
 215         run_tests(true);
 216
 217         return EXIT_SUCCESS;
 218 }