libfuse
mount.fuse.c
1 /*
2  FUSE: Filesystem in Userspace
3  Copyright (C) 2001-2007 Miklos Szeredi <miklos@szeredi.hu>
4 
5  This program can be distributed under the terms of the GNU GPL.
6  See the file COPYING.
7 */
8 
9 #include "config.h"
10 
11 #include <stdio.h>
12 #include <stdlib.h>
13 #include <string.h>
14 #include <unistd.h>
15 #include <errno.h>
16 #include <stdint.h>
17 #include <fcntl.h>
18 #include <pwd.h>
19 #include <sys/wait.h>
20 
21 #ifdef linux
22 #include <sys/prctl.h>
23 #include <sys/syscall.h>
24 #include <linux/capability.h>
25 #include <linux/securebits.h>
26 /* for 2.6 kernels */
27 #if !defined(SECBIT_KEEP_CAPS) && defined(SECURE_KEEP_CAPS)
28 #define SECBIT_KEEP_CAPS (issecure_mask(SECURE_KEEP_CAPS))
29 #endif
30 #if !defined(SECBIT_KEEP_CAPS_LOCKED) && defined(SECURE_KEEP_CAPS_LOCKED)
31 #define SECBIT_KEEP_CAPS_LOCKED (issecure_mask(SECURE_KEEP_CAPS_LOCKED))
32 #endif
33 #if !defined(SECBIT_NO_SETUID_FIXUP) && defined(SECURE_NO_SETUID_FIXUP)
34 #define SECBIT_NO_SETUID_FIXUP (issecure_mask(SECURE_NO_SETUID_FIXUP))
35 #endif
36 #if !defined(SECBIT_NO_SETUID_FIXUP_LOCKED) && defined(SECURE_NO_SETUID_FIXUP_LOCKED)
37 #define SECBIT_NO_SETUID_FIXUP_LOCKED (issecure_mask(SECURE_NO_SETUID_FIXUP_LOCKED))
38 #endif
39 #if !defined(SECBIT_NOROOT) && defined(SECURE_NOROOT)
40 #define SECBIT_NOROOT (issecure_mask(SECURE_NOROOT))
41 #endif
42 #if !defined(SECBIT_NOROOT_LOCKED) && defined(SECURE_NOROOT_LOCKED)
43 #define SECBIT_NOROOT_LOCKED (issecure_mask(SECURE_NOROOT_LOCKED))
44 #endif
45 #endif
46 
47 #include "fuse.h"
48 
49 static char *progname;
50 
51 static char *xstrdup(const char *s)
52 {
53  char *t = strdup(s);
54  if (!t) {
55  fprintf(stderr, "%s: failed to allocate memory\n", progname);
56  exit(1);
57  }
58  return t;
59 }
60 
61 static void *xrealloc(void *oldptr, size_t size)
62 {
63  void *ptr = realloc(oldptr, size);
64  if (!ptr) {
65  fprintf(stderr, "%s: failed to allocate memory\n", progname);
66  exit(1);
67  }
68  return ptr;
69 }
70 
71 static void add_arg(char **cmdp, const char *opt)
72 {
73  size_t optlen = strlen(opt);
74  size_t cmdlen = *cmdp ? strlen(*cmdp) : 0;
75  if (optlen >= (SIZE_MAX - cmdlen - 4)/4) {
76  fprintf(stderr, "%s: argument too long\n", progname);
77  exit(1);
78  }
79  char *cmd = xrealloc(*cmdp, cmdlen + optlen * 4 + 4);
80  char *s;
81  s = cmd + cmdlen;
82  if (*cmdp)
83  *s++ = ' ';
84 
85  *s++ = '\'';
86  for (; *opt; opt++) {
87  if (*opt == '\'') {
88  *s++ = '\'';
89  *s++ = '\\';
90  *s++ = '\'';
91  *s++ = '\'';
92  } else
93  *s++ = *opt;
94  }
95  *s++ = '\'';
96  *s = '\0';
97  *cmdp = cmd;
98 }
99 
100 static char *add_option(const char *opt, char *options)
101 {
102  int oldlen = options ? strlen(options) : 0;
103 
104  options = xrealloc(options, oldlen + 1 + strlen(opt) + 1);
105  if (!oldlen)
106  strcpy(options, opt);
107  else {
108  strcat(options, ",");
109  strcat(options, opt);
110  }
111  return options;
112 }
113 
114 static int prepare_fuse_fd(const char *mountpoint, const char* subtype,
115  const char *options)
116 {
117  int fuse_fd = -1;
118  int flags = -1;
119  int subtype_len = strlen(subtype) + 9;
120  char* options_copy = xrealloc(NULL, subtype_len);
121 
122  snprintf(options_copy, subtype_len, "subtype=%s", subtype);
123  options_copy = add_option(options, options_copy);
124  fuse_fd = fuse_open_channel(mountpoint, options_copy);
125  if (fuse_fd == -1) {
126  exit(1);
127  }
128 
129  flags = fcntl(fuse_fd, F_GETFD);
130  if (flags == -1 || fcntl(fuse_fd, F_SETFD, flags & ~FD_CLOEXEC) == 1) {
131  fprintf(stderr, "%s: Failed to clear CLOEXEC: %s\n",
132  progname, strerror(errno));
133  exit(1);
134  }
135 
136  return fuse_fd;
137 }
138 
139 #ifdef linux
140 static uint64_t get_capabilities(void)
141 {
142  /*
143  * This invokes the capset syscall directly to avoid the libcap
144  * dependency, which isn't really justified just for this.
145  */
146  struct __user_cap_header_struct header = {
147  .version = _LINUX_CAPABILITY_VERSION_3,
148  .pid = 0,
149  };
150  struct __user_cap_data_struct data[2];
151  memset(data, 0, sizeof(data));
152  if (syscall(SYS_capget, &header, data) == -1) {
153  fprintf(stderr, "%s: Failed to get capabilities: %s\n",
154  progname, strerror(errno));
155  exit(1);
156  }
157 
158  return data[0].effective | ((uint64_t) data[1].effective << 32);
159 }
160 
161 static void set_capabilities(uint64_t caps)
162 {
163  /*
164  * This invokes the capset syscall directly to avoid the libcap
165  * dependency, which isn't really justified just for this.
166  */
167  struct __user_cap_header_struct header = {
168  .version = _LINUX_CAPABILITY_VERSION_3,
169  .pid = 0,
170  };
171  struct __user_cap_data_struct data[2];
172  memset(data, 0, sizeof(data));
173  data[0].effective = data[0].permitted = caps;
174  data[1].effective = data[1].permitted = caps >> 32;
175  if (syscall(SYS_capset, &header, data) == -1) {
176  fprintf(stderr, "%s: Failed to set capabilities: %s\n",
177  progname, strerror(errno));
178  exit(1);
179  }
180 }
181 
182 static void drop_and_lock_capabilities(void)
183 {
184  /* Set and lock securebits. */
185  if (prctl(PR_SET_SECUREBITS,
186  SECBIT_KEEP_CAPS_LOCKED |
187  SECBIT_NO_SETUID_FIXUP |
188  SECBIT_NO_SETUID_FIXUP_LOCKED |
189  SECBIT_NOROOT |
190  SECBIT_NOROOT_LOCKED) == -1) {
191  fprintf(stderr, "%s: Failed to set securebits %s\n",
192  progname, strerror(errno));
193  exit(1);
194  }
195 
196  /* Clear the capability bounding set. */
197  int cap;
198  for (cap = 0; ; cap++) {
199  int cap_status = prctl(PR_CAPBSET_READ, cap);
200  if (cap_status == 0) {
201  continue;
202  }
203  if (cap_status == -1 && errno == EINVAL) {
204  break;
205  }
206 
207  if (cap_status != 1) {
208  fprintf(stderr,
209  "%s: Failed to get capability %u: %s\n",
210  progname, cap, strerror(errno));
211  exit(1);
212  }
213  if (prctl(PR_CAPBSET_DROP, cap) == -1) {
214  fprintf(stderr,
215  "%s: Failed to drop capability %u: %s\n",
216  progname, cap, strerror(errno));
217  }
218  }
219 
220  /* Drop capabilities. */
221  set_capabilities(0);
222 
223  /* Prevent re-acquisition of privileges. */
224  if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) == -1) {
225  fprintf(stderr, "%s: Failed to set no_new_privs: %s\n",
226  progname, strerror(errno));
227  exit(1);
228  }
229 }
230 #endif
231 
232 int main(int argc, char *argv[])
233 {
234  char *type = NULL;
235  char *source;
236  const char *mountpoint;
237  char *basename;
238  char *options = NULL;
239  char *command = NULL;
240  char *setuid_name = NULL;
241  int i;
242  int dev = 1;
243  int suid = 1;
244  int pass_fuse_fd = 0;
245  int drop_privileges = 0;
246 
247  progname = argv[0];
248  basename = strrchr(argv[0], '/');
249  if (basename)
250  basename++;
251  else
252  basename = argv[0];
253 
254  if (strncmp(basename, "mount.fuse.", 11) == 0)
255  type = basename + 11;
256  if (strncmp(basename, "mount.fuseblk.", 14) == 0)
257  type = basename + 14;
258 
259  if (type && !type[0])
260  type = NULL;
261 
262  if (argc < 3) {
263  fprintf(stderr,
264  "usage: %s %s destination [-t type] [-o opt[,opts...]]\n",
265  progname, type ? "source" : "type#[source]");
266  exit(1);
267  }
268 
269  source = argv[1];
270  if (!source[0])
271  source = NULL;
272 
273  mountpoint = argv[2];
274 
275  for (i = 3; i < argc; i++) {
276  if (strcmp(argv[i], "-v") == 0) {
277  continue;
278  } else if (strcmp(argv[i], "-t") == 0) {
279  i++;
280 
281  if (i == argc) {
282  fprintf(stderr,
283  "%s: missing argument to option '-t'\n",
284  progname);
285  exit(1);
286  }
287  type = argv[i];
288  if (strncmp(type, "fuse.", 5) == 0)
289  type += 5;
290  else if (strncmp(type, "fuseblk.", 8) == 0)
291  type += 8;
292 
293  if (!type[0]) {
294  fprintf(stderr,
295  "%s: empty type given as argument to option '-t'\n",
296  progname);
297  exit(1);
298  }
299  } else if (strcmp(argv[i], "-o") == 0) {
300  char *opts;
301  char *opt;
302  i++;
303  if (i == argc)
304  break;
305 
306  opts = xstrdup(argv[i]);
307  opt = strtok(opts, ",");
308  while (opt) {
309  int j;
310  int ignore = 0;
311  const char *ignore_opts[] = { "",
312  "user",
313  "nofail",
314  "nouser",
315  "users",
316  "auto",
317  "noauto",
318  "_netdev",
319  NULL};
320  if (strncmp(opt, "setuid=", 7) == 0) {
321  setuid_name = xstrdup(opt + 7);
322  ignore = 1;
323  } else if (strcmp(opt,
324  "drop_privileges") == 0) {
325  pass_fuse_fd = 1;
326  drop_privileges = 1;
327  ignore = 1;
328  }
329  for (j = 0; ignore_opts[j]; j++)
330  if (strcmp(opt, ignore_opts[j]) == 0)
331  ignore = 1;
332 
333  if (!ignore) {
334  if (strcmp(opt, "nodev") == 0)
335  dev = 0;
336  else if (strcmp(opt, "nosuid") == 0)
337  suid = 0;
338 
339  options = add_option(opt, options);
340  }
341  opt = strtok(NULL, ",");
342  }
343  }
344  }
345 
346  if (drop_privileges) {
347  uint64_t required_caps = CAP_TO_MASK(CAP_SETPCAP) |
348  CAP_TO_MASK(CAP_SYS_ADMIN);
349  if ((get_capabilities() & required_caps) != required_caps) {
350  fprintf(stderr, "%s: drop_privileges was requested, which launches the FUSE file system fully unprivileged. In order to do so %s must be run with privileges, please invoke with CAP_SYS_ADMIN and CAP_SETPCAP (e.g. as root).\n",
351  progname, progname);
352  exit(1);
353  }
354  }
355 
356  if (dev)
357  options = add_option("dev", options);
358  if (suid)
359  options = add_option("suid", options);
360 
361  if (!type) {
362  if (source) {
363  type = xstrdup(source);
364  source = strchr(type, '#');
365  if (source)
366  *source++ = '\0';
367  if (!type[0]) {
368  fprintf(stderr, "%s: empty filesystem type\n",
369  progname);
370  exit(1);
371  }
372  } else {
373  fprintf(stderr, "%s: empty source\n", progname);
374  exit(1);
375  }
376  }
377 
378  if (setuid_name && setuid_name[0]) {
379 #ifdef linux
380  if (drop_privileges) {
381  /*
382  * Make securebits more permissive before calling
383  * setuid(). Specifically, if SECBIT_KEEP_CAPS and
384  * SECBIT_NO_SETUID_FIXUP weren't set, setuid() would
385  * have the side effect of dropping all capabilities,
386  * and we need to retain CAP_SETPCAP in order to drop
387  * all privileges before exec().
388  */
389  if (prctl(PR_SET_SECUREBITS,
390  SECBIT_KEEP_CAPS |
391  SECBIT_NO_SETUID_FIXUP) == -1) {
392  fprintf(stderr,
393  "%s: Failed to set securebits %s\n",
394  progname, strerror(errno));
395  exit(1);
396  }
397  }
398 #endif
399 
400  struct passwd *pwd = getpwnam(setuid_name);
401  if (setgid(pwd->pw_gid) == -1 || setuid(pwd->pw_uid) == -1) {
402  fprintf(stderr, "%s: Failed to setuid to %s: %s\n",
403  progname, setuid_name, strerror(errno));
404  exit(1);
405  }
406  } else if (!getenv("HOME")) {
407  /* Hack to make filesystems work in the boot environment */
408  setenv("HOME", "/root", 0);
409  }
410 
411  if (pass_fuse_fd) {
412  int fuse_fd = prepare_fuse_fd(mountpoint, type, options);
413  char *dev_fd_mountpoint = xrealloc(NULL, 20);
414  snprintf(dev_fd_mountpoint, 20, "/dev/fd/%u", fuse_fd);
415  mountpoint = dev_fd_mountpoint;
416  }
417 
418 #ifdef linux
419  if (drop_privileges) {
420  drop_and_lock_capabilities();
421  }
422 #endif
423  add_arg(&command, type);
424  if (source)
425  add_arg(&command, source);
426  add_arg(&command, mountpoint);
427  if (options) {
428  add_arg(&command, "-o");
429  add_arg(&command, options);
430  }
431 
432  execl("/bin/sh", "/bin/sh", "-c", command, NULL);
433  fprintf(stderr, "%s: failed to execute /bin/sh: %s\n", progname,
434  strerror(errno));
435  return 1;
436 }
int fuse_open_channel(const char *mountpoint, const char *options)
Definition: helper.c:424