selftests/mount/nosymfollow-test.c

0001 // SPDX-License-Identifier: GPL-2.0
0002 #define _GNU_SOURCE
0003 #include <errno.h>
0004 #include <fcntl.h>
0005 #include <limits.h>
0006 #include <sched.h>
0007 #include <stdarg.h>
0008 #include <stdbool.h>
0009 #include <stdio.h>
0010 #include <stdlib.h>
0011 #include <string.h>
0012 #include <sys/mount.h>
0013 #include <sys/stat.h>
0014 #include <sys/types.h>
0015 #include <sys/vfs.h>
0016 #include <unistd.h>
0017
0018 #ifndef MS_NOSYMFOLLOW
0019 # define MS_NOSYMFOLLOW 256     /* Do not follow symlinks */
0020 #endif
0021
0022 #ifndef ST_NOSYMFOLLOW
0023 # define ST_NOSYMFOLLOW 0x2000  /* Do not follow symlinks */
0024 #endif
0025
0026 #define DATA "/tmp/data"
0027 #define LINK "/tmp/symlink"
0028 #define TMP  "/tmp"
0029
0030 static void die(char *fmt, ...)
0031 {
0032     va_list ap;
0033
0034     va_start(ap, fmt);
0035     vfprintf(stderr, fmt, ap);
0036     va_end(ap);
0037     exit(EXIT_FAILURE);
0038 }
0039
0040 static void vmaybe_write_file(bool enoent_ok, char *filename, char *fmt,
0041         va_list ap)
0042 {
0043     ssize_t written;
0044     char buf[4096];
0045     int buf_len;
0046     int fd;
0047
0048     buf_len = vsnprintf(buf, sizeof(buf), fmt, ap);
0049     if (buf_len < 0)
0050         die("vsnprintf failed: %s\n", strerror(errno));
0051
0052     if (buf_len >= sizeof(buf))
0053         die("vsnprintf output truncated\n");
0054
0055     fd = open(filename, O_WRONLY);
0056     if (fd < 0) {
0057         if ((errno == ENOENT) && enoent_ok)
0058             return;
0059         die("open of %s failed: %s\n", filename, strerror(errno));
0060     }
0061
0062     written = write(fd, buf, buf_len);
0063     if (written != buf_len) {
0064         if (written >= 0) {
0065             die("short write to %s\n", filename);
0066         } else {
0067             die("write to %s failed: %s\n",
0068                 filename, strerror(errno));
0069         }
0070     }
0071
0072     if (close(fd) != 0)
0073         die("close of %s failed: %s\n", filename, strerror(errno));
0074 }
0075
0076 static void maybe_write_file(char *filename, char *fmt, ...)
0077 {
0078     va_list ap;
0079
0080     va_start(ap, fmt);
0081     vmaybe_write_file(true, filename, fmt, ap);
0082     va_end(ap);
0083 }
0084
0085 static void write_file(char *filename, char *fmt, ...)
0086 {
0087     va_list ap;
0088
0089     va_start(ap, fmt);
0090     vmaybe_write_file(false, filename, fmt, ap);
0091     va_end(ap);
0092 }
0093
0094 static void create_and_enter_ns(void)
0095 {
0096     uid_t uid = getuid();
0097     gid_t gid = getgid();
0098
0099     if (unshare(CLONE_NEWUSER) != 0)
0100         die("unshare(CLONE_NEWUSER) failed: %s\n", strerror(errno));
0101
0102     maybe_write_file("/proc/self/setgroups", "deny");
0103     write_file("/proc/self/uid_map", "0 %d 1", uid);
0104     write_file("/proc/self/gid_map", "0 %d 1", gid);
0105
0106     if (setgid(0) != 0)
0107         die("setgid(0) failed %s\n", strerror(errno));
0108     if (setuid(0) != 0)
0109         die("setuid(0) failed %s\n", strerror(errno));
0110
0111     if (unshare(CLONE_NEWNS) != 0)
0112         die("unshare(CLONE_NEWNS) failed: %s\n", strerror(errno));
0113 }
0114
0115 static void setup_symlink(void)
0116 {
0117     int data, err;
0118
0119     data = creat(DATA, O_RDWR);
0120     if (data < 0)
0121         die("creat failed: %s\n", strerror(errno));
0122
0123     err = symlink(DATA, LINK);
0124     if (err < 0)
0125         die("symlink failed: %s\n", strerror(errno));
0126
0127     if (close(data) != 0)
0128         die("close of %s failed: %s\n", DATA, strerror(errno));
0129 }
0130
0131 static void test_link_traversal(bool nosymfollow)
0132 {
0133     int link;
0134
0135     link = open(LINK, 0, O_RDWR);
0136     if (nosymfollow) {
0137         if ((link != -1 || errno != ELOOP)) {
0138             die("link traversal unexpected result: %d, %s\n",
0139                     link, strerror(errno));
0140         }
0141     } else {
0142         if (link < 0)
0143             die("link traversal failed: %s\n", strerror(errno));
0144
0145         if (close(link) != 0)
0146             die("close of link failed: %s\n", strerror(errno));
0147     }
0148 }
0149
0150 static void test_readlink(void)
0151 {
0152     char buf[4096];
0153     ssize_t ret;
0154
0155     bzero(buf, sizeof(buf));
0156
0157     ret = readlink(LINK, buf, sizeof(buf));
0158     if (ret < 0)
0159         die("readlink failed: %s\n", strerror(errno));
0160     if (strcmp(buf, DATA) != 0)
0161         die("readlink strcmp failed: '%s' '%s'\n", buf, DATA);
0162 }
0163
0164 static void test_realpath(void)
0165 {
0166     char *path = realpath(LINK, NULL);
0167
0168     if (!path)
0169         die("realpath failed: %s\n", strerror(errno));
0170     if (strcmp(path, DATA) != 0)
0171         die("realpath strcmp failed\n");
0172
0173     free(path);
0174 }
0175
0176 static void test_statfs(bool nosymfollow)
0177 {
0178     struct statfs buf;
0179     int ret;
0180
0181     ret = statfs(TMP, &buf);
0182     if (ret)
0183         die("statfs failed: %s\n", strerror(errno));
0184
0185     if (nosymfollow) {
0186         if ((buf.f_flags & ST_NOSYMFOLLOW) == 0)
0187             die("ST_NOSYMFOLLOW not set on %s\n", TMP);
0188     } else {
0189         if ((buf.f_flags & ST_NOSYMFOLLOW) != 0)
0190             die("ST_NOSYMFOLLOW set on %s\n", TMP);
0191     }
0192 }
0193
0194 static void run_tests(bool nosymfollow)
0195 {
0196     test_link_traversal(nosymfollow);
0197     test_readlink();
0198     test_realpath();
0199     test_statfs(nosymfollow);
0200 }
0201
0202 int main(int argc, char **argv)
0203 {
0204     create_and_enter_ns();
0205
0206     if (mount("testing", TMP, "ramfs", 0, NULL) != 0)
0207         die("mount failed: %s\n", strerror(errno));
0208
0209     setup_symlink();
0210     run_tests(false);
0211
0212     if (mount("testing", TMP, "ramfs", MS_REMOUNT|MS_NOSYMFOLLOW, NULL) != 0)
0213         die("remount failed: %s\n", strerror(errno));
0214
0215     run_tests(true);
0216
0217     return EXIT_SUCCESS;
0218 }