tor  0.4.1.0-alpha-dev
setuid.c
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1 /* Copyright (c) 2003, Roger Dingledine
2  * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
3  * Copyright (c) 2007-2019, The Tor Project, Inc. */
4 /* See LICENSE for licensing information */
5 
11 #include "orconfig.h"
12 #include "lib/process/setuid.h"
13 
14 #if defined(HAVE_SYS_CAPABILITY_H) && defined(HAVE_CAP_SET_PROC)
15 #define HAVE_LINUX_CAPABILITIES
16 #endif
17 
19 #include "lib/fs/userdb.h"
20 #include "lib/log/log.h"
21 #include "lib/log/util_bug.h"
22 #include "lib/malloc/malloc.h"
23 
24 #ifdef HAVE_SYS_TYPES_H
25 #include <sys/types.h>
26 #endif
27 #ifdef HAVE_UNISTD_H
28 #include <unistd.h>
29 #endif
30 #ifdef HAVE_GRP_H
31 #include <grp.h>
32 #endif
33 #ifdef HAVE_PWD_H
34 #include <pwd.h>
35 #endif
36 #ifdef HAVE_SYS_CAPABILITY_H
37 #include <sys/capability.h>
38 #endif
39 #ifdef HAVE_SYS_PRCTL_H
40 #include <sys/prctl.h>
41 #endif
42 
43 #include <errno.h>
44 #include <string.h>
45 
46 #ifndef _WIN32
47 
50 static int
52 {
54 #define CREDENTIAL_LOG_LEVEL LOG_INFO
55  /* Real, effective and saved UIDs */
56  uid_t ruid, euid, suid;
57  /* Read, effective and saved GIDs */
58  gid_t rgid, egid, sgid;
59  /* Supplementary groups */
60  gid_t *sup_gids = NULL;
61  int sup_gids_size;
62  /* Number of supplementary groups */
63  int ngids;
64 
65  /* log UIDs */
66 #ifdef HAVE_GETRESUID
67  if (getresuid(&ruid, &euid, &suid) != 0 ) {
68  log_warn(LD_GENERAL, "Error getting changed UIDs: %s", strerror(errno));
69  return -1;
70  } else {
71  log_fn(CREDENTIAL_LOG_LEVEL, LD_GENERAL,
72  "UID is %u (real), %u (effective), %u (saved)",
73  (unsigned)ruid, (unsigned)euid, (unsigned)suid);
74  }
75 #else /* !(defined(HAVE_GETRESUID)) */
76  /* getresuid is not present on MacOS X, so we can't get the saved (E)UID */
77  ruid = getuid();
78  euid = geteuid();
79  (void)suid;
80 
81  log_fn(CREDENTIAL_LOG_LEVEL, LD_GENERAL,
82  "UID is %u (real), %u (effective), unknown (saved)",
83  (unsigned)ruid, (unsigned)euid);
84 #endif /* defined(HAVE_GETRESUID) */
85 
86  /* log GIDs */
87 #ifdef HAVE_GETRESGID
88  if (getresgid(&rgid, &egid, &sgid) != 0 ) {
89  log_warn(LD_GENERAL, "Error getting changed GIDs: %s", strerror(errno));
90  return -1;
91  } else {
92  log_fn(CREDENTIAL_LOG_LEVEL, LD_GENERAL,
93  "GID is %u (real), %u (effective), %u (saved)",
94  (unsigned)rgid, (unsigned)egid, (unsigned)sgid);
95  }
96 #else /* !(defined(HAVE_GETRESGID)) */
97  /* getresgid is not present on MacOS X, so we can't get the saved (E)GID */
98  rgid = getgid();
99  egid = getegid();
100  (void)sgid;
101  log_fn(CREDENTIAL_LOG_LEVEL, LD_GENERAL,
102  "GID is %u (real), %u (effective), unknown (saved)",
103  (unsigned)rgid, (unsigned)egid);
104 #endif /* defined(HAVE_GETRESGID) */
105 
106  /* log supplementary groups */
107  sup_gids_size = 64;
108  sup_gids = tor_calloc(64, sizeof(gid_t));
109  while ((ngids = getgroups(sup_gids_size, sup_gids)) < 0 &&
110  errno == EINVAL &&
111  sup_gids_size < NGROUPS_MAX) {
112  sup_gids_size *= 2;
113  sup_gids = tor_reallocarray(sup_gids, sizeof(gid_t), sup_gids_size);
114  }
115 
116  if (ngids < 0) {
117  log_warn(LD_GENERAL, "Error getting supplementary GIDs: %s",
118  strerror(errno));
119  tor_free(sup_gids);
120  return -1;
121  } else {
122  int i, retval = 0;
123  char *s = NULL;
124  smartlist_t *elts = smartlist_new();
125 
126  for (i = 0; i<ngids; i++) {
127  smartlist_add_asprintf(elts, "%u", (unsigned)sup_gids[i]);
128  }
129 
130  s = smartlist_join_strings(elts, " ", 0, NULL);
131 
132  log_fn(CREDENTIAL_LOG_LEVEL, LD_GENERAL, "Supplementary groups are: %s",s);
133 
134  tor_free(s);
135  SMARTLIST_FOREACH(elts, char *, cp, tor_free(cp));
136  smartlist_free(elts);
137  tor_free(sup_gids);
138 
139  return retval;
140  }
141 
142  return 0;
143 }
144 #endif /* !defined(_WIN32) */
145 
148 int
150 {
151 #ifdef HAVE_LINUX_CAPABILITIES
152  cap_t caps = cap_get_proc();
153  if (caps == NULL)
154  return 0;
155  cap_free(caps);
156  return 1;
157 #else /* !(defined(HAVE_LINUX_CAPABILITIES)) */
158  return 0;
159 #endif /* defined(HAVE_LINUX_CAPABILITIES) */
160 }
161 
162 #ifdef HAVE_LINUX_CAPABILITIES
163 
175 static int
176 drop_capabilities(int pre_setuid)
177 {
178  /* We keep these three capabilities, and these only, as we setuid.
179  * After we setuid, we drop all but the first. */
180  const cap_value_t caplist[] = {
181  CAP_NET_BIND_SERVICE, CAP_SETUID, CAP_SETGID
182  };
183  const char *where = pre_setuid ? "pre-setuid" : "post-setuid";
184  const int n_effective = pre_setuid ? 3 : 1;
185  const int n_permitted = pre_setuid ? 3 : 1;
186  const int n_inheritable = 1;
187  const int keepcaps = pre_setuid ? 1 : 0;
188 
189  /* Sets whether we keep capabilities across a setuid. */
190  if (prctl(PR_SET_KEEPCAPS, keepcaps) < 0) {
191  log_warn(LD_CONFIG, "Unable to call prctl() %s: %s",
192  where, strerror(errno));
193  return -1;
194  }
195 
196  cap_t caps = cap_get_proc();
197  if (!caps) {
198  log_warn(LD_CONFIG, "Unable to call cap_get_proc() %s: %s",
199  where, strerror(errno));
200  return -1;
201  }
202  cap_clear(caps);
203 
204  cap_set_flag(caps, CAP_EFFECTIVE, n_effective, caplist, CAP_SET);
205  cap_set_flag(caps, CAP_PERMITTED, n_permitted, caplist, CAP_SET);
206  cap_set_flag(caps, CAP_INHERITABLE, n_inheritable, caplist, CAP_SET);
207 
208  int r = cap_set_proc(caps);
209  cap_free(caps);
210  if (r < 0) {
211  log_warn(LD_CONFIG, "No permission to set capabilities %s: %s",
212  where, strerror(errno));
213  return -1;
214  }
215 
216  return 0;
217 }
218 #endif /* defined(HAVE_LINUX_CAPABILITIES) */
219 
229 int
230 switch_id(const char *user, const unsigned flags)
231 {
232 #ifndef _WIN32
233  const struct passwd *pw = NULL;
234  uid_t old_uid;
235  gid_t old_gid;
236  static int have_already_switched_id = 0;
237  const int keep_bindlow = !!(flags & SWITCH_ID_KEEP_BINDLOW);
238  const int warn_if_no_caps = !!(flags & SWITCH_ID_WARN_IF_NO_CAPS);
239 
240  tor_assert(user);
241 
242  if (have_already_switched_id)
243  return 0;
244 
245  /* Log the initial credential state */
246  if (log_credential_status())
247  return -1;
248 
249  log_fn(CREDENTIAL_LOG_LEVEL, LD_GENERAL, "Changing user and groups");
250 
251  /* Get old UID/GID to check if we changed correctly */
252  old_uid = getuid();
253  old_gid = getgid();
254 
255  /* Lookup the user and group information, if we have a problem, bail out. */
256  pw = tor_getpwnam(user);
257  if (pw == NULL) {
258  log_warn(LD_CONFIG, "Error setting configured user: %s not found", user);
259  return -1;
260  }
261 
262 #ifdef HAVE_LINUX_CAPABILITIES
263  (void) warn_if_no_caps;
264  if (keep_bindlow) {
265  if (drop_capabilities(1))
266  return -1;
267  }
268 #else /* !(defined(HAVE_LINUX_CAPABILITIES)) */
269  (void) keep_bindlow;
270  if (warn_if_no_caps) {
271  log_warn(LD_CONFIG, "KeepBindCapabilities set, but no capability support "
272  "on this system.");
273  }
274 #endif /* defined(HAVE_LINUX_CAPABILITIES) */
275 
276  /* Properly switch egid,gid,euid,uid here or bail out */
277  if (setgroups(1, &pw->pw_gid)) {
278  log_warn(LD_GENERAL, "Error setting groups to gid %d: \"%s\".",
279  (int)pw->pw_gid, strerror(errno));
280  if (old_uid == pw->pw_uid) {
281  log_warn(LD_GENERAL, "Tor is already running as %s. You do not need "
282  "the \"User\" option if you are already running as the user "
283  "you want to be. (If you did not set the User option in your "
284  "torrc, check whether it was specified on the command line "
285  "by a startup script.)", user);
286  } else {
287  log_warn(LD_GENERAL, "If you set the \"User\" option, you must start Tor"
288  " as root.");
289  }
290  return -1;
291  }
292 
293  if (setegid(pw->pw_gid)) {
294  log_warn(LD_GENERAL, "Error setting egid to %d: %s",
295  (int)pw->pw_gid, strerror(errno));
296  return -1;
297  }
298 
299  if (setgid(pw->pw_gid)) {
300  log_warn(LD_GENERAL, "Error setting gid to %d: %s",
301  (int)pw->pw_gid, strerror(errno));
302  return -1;
303  }
304 
305  if (setuid(pw->pw_uid)) {
306  log_warn(LD_GENERAL, "Error setting configured uid to %s (%d): %s",
307  user, (int)pw->pw_uid, strerror(errno));
308  return -1;
309  }
310 
311  if (seteuid(pw->pw_uid)) {
312  log_warn(LD_GENERAL, "Error setting configured euid to %s (%d): %s",
313  user, (int)pw->pw_uid, strerror(errno));
314  return -1;
315  }
316 
317  /* This is how OpenBSD rolls:
318  if (setgroups(1, &pw->pw_gid) || setegid(pw->pw_gid) ||
319  setgid(pw->pw_gid) || setuid(pw->pw_uid) || seteuid(pw->pw_uid)) {
320  setgid(pw->pw_gid) || seteuid(pw->pw_uid) || setuid(pw->pw_uid)) {
321  log_warn(LD_GENERAL, "Error setting configured UID/GID: %s",
322  strerror(errno));
323  return -1;
324  }
325  */
326 
327  /* We've properly switched egid, gid, euid, uid, and supplementary groups if
328  * we're here. */
329 #ifdef HAVE_LINUX_CAPABILITIES
330  if (keep_bindlow) {
331  if (drop_capabilities(0))
332  return -1;
333  }
334 #endif /* defined(HAVE_LINUX_CAPABILITIES) */
335 
336 #if !defined(CYGWIN) && !defined(__CYGWIN__)
337  /* If we tried to drop privilege to a group/user other than root, attempt to
338  * restore root (E)(U|G)ID, and abort if the operation succeeds */
339 
340  /* Only check for privilege dropping if we were asked to be non-root */
341  if (pw->pw_uid) {
342  /* Try changing GID/EGID */
343  if (pw->pw_gid != old_gid &&
344  (setgid(old_gid) != -1 || setegid(old_gid) != -1)) {
345  log_warn(LD_GENERAL, "Was able to restore group credentials even after "
346  "switching GID: this means that the setgid code didn't work.");
347  return -1;
348  }
349 
350  /* Try changing UID/EUID */
351  if (pw->pw_uid != old_uid &&
352  (setuid(old_uid) != -1 || seteuid(old_uid) != -1)) {
353  log_warn(LD_GENERAL, "Was able to restore user credentials even after "
354  "switching UID: this means that the setuid code didn't work.");
355  return -1;
356  }
357  }
358 #endif /* !defined(CYGWIN) && !defined(__CYGWIN__) */
359 
360  /* Check what really happened */
361  if (log_credential_status()) {
362  return -1;
363  }
364 
365  have_already_switched_id = 1; /* mark success so we never try again */
366 
367 #if defined(__linux__) && defined(HAVE_SYS_PRCTL_H) && \
368  defined(HAVE_PRCTL) && defined(PR_SET_DUMPABLE)
369  if (pw->pw_uid) {
370  /* Re-enable core dumps if we're not running as root. */
371  log_info(LD_CONFIG, "Re-enabling coredumps");
372  if (prctl(PR_SET_DUMPABLE, 1)) {
373  log_warn(LD_CONFIG, "Unable to re-enable coredumps: %s",strerror(errno));
374  }
375  }
376 #endif /* defined(__linux__) && defined(HAVE_SYS_PRCTL_H) && ... */
377  return 0;
378 
379 #else /* !(!defined(_WIN32)) */
380  (void)user;
381  (void)flags;
382 
383  log_warn(LD_CONFIG, "Switching users is unsupported on your OS.");
384  return -1;
385 #endif /* !defined(_WIN32) */
386 }
Header for smartlist.c.
#define SWITCH_ID_KEEP_BINDLOW
Definition: setuid.h:17
#define LD_GENERAL
Definition: log.h:58
const struct passwd * tor_getpwnam(const char *username)
Definition: userdb.c:70
static int log_credential_status(void)
Definition: setuid.c:51
#define tor_free(p)
Definition: malloc.h:52
Headers for util_malloc.c.
int switch_id(const char *user, const unsigned flags)
Definition: setuid.c:230
tor_assert(buffer)
Header for setuid.c.
void smartlist_add_asprintf(struct smartlist_t *sl, const char *pattern,...)
Definition: smartlist.c:36
int have_capability_support(void)
Definition: setuid.c:149
char * smartlist_join_strings(smartlist_t *sl, const char *join, int terminate, size_t *len_out)
Definition: smartlist.c:279
#define SMARTLIST_FOREACH(sl, type, var, cmd)
#define log_fn(severity, domain, args,...)
Definition: log.h:255
Headers for log.c.
#define SWITCH_ID_WARN_IF_NO_CAPS
Definition: setuid.h:19
Header for userdb.c.
Macros to manage assertions, fatal and non-fatal.
#define LD_CONFIG
Definition: log.h:64