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 GPLv2.
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  char *dup_source = NULL;
237  const char *mountpoint;
238  char *basename;
239  char *options = NULL;
240  char *command = NULL;
241  char *setuid_name = NULL;
242  int i;
243  int dev = 1;
244  int suid = 1;
245  int pass_fuse_fd = 0;
246  int drop_privileges = 0;
247  char *dev_fd_mountpoint = NULL;
248 
249  progname = argv[0];
250  basename = strrchr(argv[0], '/');
251  if (basename)
252  basename++;
253  else
254  basename = argv[0];
255 
256  if (strncmp(basename, "mount.fuse.", 11) == 0)
257  type = basename + 11;
258  if (strncmp(basename, "mount.fuseblk.", 14) == 0)
259  type = basename + 14;
260 
261  if (type && !type[0])
262  type = NULL;
263 
264  if (argc < 3) {
265  fprintf(stderr,
266  "usage: %s %s destination [-t type] [-o opt[,opts...]]\n",
267  progname, type ? "source" : "type#[source]");
268  exit(1);
269  }
270 
271  source = argv[1];
272  if (!source[0])
273  source = NULL;
274 
275  mountpoint = argv[2];
276 
277  for (i = 3; i < argc; i++) {
278  if (strcmp(argv[i], "-v") == 0) {
279  continue;
280  } else if (strcmp(argv[i], "-t") == 0) {
281  i++;
282 
283  if (i == argc) {
284  fprintf(stderr,
285  "%s: missing argument to option '-t'\n",
286  progname);
287  exit(1);
288  }
289  type = argv[i];
290  if (strncmp(type, "fuse.", 5) == 0)
291  type += 5;
292  else if (strncmp(type, "fuseblk.", 8) == 0)
293  type += 8;
294 
295  if (!type[0]) {
296  fprintf(stderr,
297  "%s: empty type given as argument to option '-t'\n",
298  progname);
299  exit(1);
300  }
301  } else if (strcmp(argv[i], "-o") == 0) {
302  char *opts;
303  char *opt;
304  i++;
305  if (i == argc)
306  break;
307 
308  opts = xstrdup(argv[i]);
309  opt = strtok(opts, ",");
310  while (opt) {
311  int j;
312  int ignore = 0;
313  const char *ignore_opts[] = { "",
314  "user",
315  "nofail",
316  "nouser",
317  "users",
318  "auto",
319  "noauto",
320  "_netdev",
321  NULL};
322  if (strncmp(opt, "setuid=", 7) == 0) {
323  setuid_name = xstrdup(opt + 7);
324  ignore = 1;
325  } else if (strcmp(opt,
326  "drop_privileges") == 0) {
327  pass_fuse_fd = 1;
328  drop_privileges = 1;
329  ignore = 1;
330  }
331  for (j = 0; ignore_opts[j]; j++)
332  if (strcmp(opt, ignore_opts[j]) == 0)
333  ignore = 1;
334 
335  if (!ignore) {
336  if (strcmp(opt, "nodev") == 0)
337  dev = 0;
338  else if (strcmp(opt, "nosuid") == 0)
339  suid = 0;
340 
341  options = add_option(opt, options);
342  }
343  opt = strtok(NULL, ",");
344  }
345  free(opts);
346  }
347  }
348 
349  if (drop_privileges) {
350  uint64_t required_caps = CAP_TO_MASK(CAP_SETPCAP) |
351  CAP_TO_MASK(CAP_SYS_ADMIN);
352  if ((get_capabilities() & required_caps) != required_caps) {
353  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",
354  progname, progname);
355  exit(1);
356  }
357  }
358 
359  if (dev)
360  options = add_option("dev", options);
361  if (suid)
362  options = add_option("suid", options);
363 
364  if (!type) {
365  if (source) {
366  dup_source = xstrdup(source);
367  type = dup_source;
368  source = strchr(type, '#');
369  if (source)
370  *source++ = '\0';
371  if (!type[0]) {
372  fprintf(stderr, "%s: empty filesystem type\n",
373  progname);
374  exit(1);
375  }
376  } else {
377  fprintf(stderr, "%s: empty source\n", progname);
378  exit(1);
379  }
380  }
381 
382  if (setuid_name && setuid_name[0]) {
383 #ifdef linux
384  if (drop_privileges) {
385  /*
386  * Make securebits more permissive before calling
387  * setuid(). Specifically, if SECBIT_KEEP_CAPS and
388  * SECBIT_NO_SETUID_FIXUP weren't set, setuid() would
389  * have the side effect of dropping all capabilities,
390  * and we need to retain CAP_SETPCAP in order to drop
391  * all privileges before exec().
392  */
393  if (prctl(PR_SET_SECUREBITS,
394  SECBIT_KEEP_CAPS |
395  SECBIT_NO_SETUID_FIXUP) == -1) {
396  fprintf(stderr,
397  "%s: Failed to set securebits %s\n",
398  progname, strerror(errno));
399  exit(1);
400  }
401  }
402 #endif
403 
404  struct passwd *pwd = getpwnam(setuid_name);
405  if (!pwd || setgid(pwd->pw_gid) == -1 || setuid(pwd->pw_uid) == -1) {
406  fprintf(stderr, "%s: Failed to setuid to %s: %s\n",
407  progname, setuid_name, strerror(errno));
408  exit(1);
409  }
410  } else if (!getenv("HOME")) {
411  /* Hack to make filesystems work in the boot environment */
412  setenv("HOME", "/root", 0);
413  }
414 
415  if (pass_fuse_fd) {
416  int fuse_fd = prepare_fuse_fd(mountpoint, type, options);
417  dev_fd_mountpoint = xrealloc(NULL, 20);
418  snprintf(dev_fd_mountpoint, 20, "/dev/fd/%u", fuse_fd);
419  mountpoint = dev_fd_mountpoint;
420  }
421 
422 #ifdef linux
423  if (drop_privileges) {
424  drop_and_lock_capabilities();
425  }
426 #endif
427  add_arg(&command, type);
428  if (source)
429  add_arg(&command, source);
430  add_arg(&command, mountpoint);
431  if (options) {
432  add_arg(&command, "-o");
433  add_arg(&command, options);
434  }
435 
436  free(options);
437  free(dev_fd_mountpoint);
438  free(dup_source);
439  free(setuid_name);
440 
441  execl("/bin/sh", "/bin/sh", "-c", command, NULL);
442  fprintf(stderr, "%s: failed to execute /bin/sh: %s\n", progname,
443  strerror(errno));
444  return 1;
445 }
int fuse_open_channel(const char *mountpoint, const char *options)
Definition: helper.c:424