source3/smbd/sec_ctx.c

   1 /*
   2    Unix SMB/CIFS implementation.
   3    uid/user handling
   4    Copyright (C) Tim Potter 2000
   5
   6    This program is free software; you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 3 of the License, or
   9    (at your option) any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  18 */
  19
  20 #include "includes.h"
  21 #include "system/passwd.h"
  22 #include "smbd/smbd.h"
  23 #include "smbd/globals.h"
  24 #include "libcli/security/security_token.h"
  25 #include "auth.h"
  26 #include "smbprofile.h"
  27
  28 extern struct current_user current_user;
  29
  30 /****************************************************************************
  31  Are two UNIX tokens equal ?
  32 ****************************************************************************/
  33
  34 bool unix_token_equal(const struct security_unix_token *t1, const struct security_unix_token *t2)
  35 {
  36         if (t1->uid != t2->uid || t1->gid != t2->gid ||
  37                         t1->ngroups != t2->ngroups) {
  38                 return false;
  39         }
  40         if (memcmp(t1->groups, t2->groups,
  41                         t1->ngroups*sizeof(gid_t)) != 0) {
  42                 return false;
  43         }
  44         return true;
  45 }
  46
  47 /****************************************************************************
  48  Become the specified uid.
  49 ****************************************************************************/
  50
  51 static bool become_uid(uid_t uid)
  52 {
  53         /* Check for dodgy uid values */
  54
  55         if (uid == (uid_t)-1 ||
  56             ((sizeof(uid_t) == 2) && (uid == (uid_t)65535))) {
  57                 if (!become_uid_done) {
  58                         DEBUG(1,("WARNING: using uid %d is a security risk\n",
  59                                  (int)uid));
  60                         become_uid_done = true;
  61                 }
  62         }
  63
  64         /* Set effective user id */
  65
  66         set_effective_uid(uid);
  67
  68         DO_PROFILE_INC(uid_changes);
  69         return True;
  70 }
  71
  72 /****************************************************************************
  73  Become the specified gid.
  74 ****************************************************************************/
  75
  76 static bool become_gid(gid_t gid)
  77 {
  78         /* Check for dodgy gid values */
  79
  80         if (gid == (gid_t)-1 || ((sizeof(gid_t) == 2) &&
  81                                  (gid == (gid_t)65535))) {
  82                 if (!become_gid_done) {
  83                         DEBUG(1,("WARNING: using gid %d is a security risk\n",
  84                                  (int)gid));
  85                         become_gid_done = true;
  86                 }
  87         }
  88
  89         /* Set effective group id */
  90
  91         set_effective_gid(gid);
  92         return True;
  93 }
  94
  95 /****************************************************************************
  96  Become the specified uid and gid.
  97 ****************************************************************************/
  98
  99 static bool become_id(uid_t uid, gid_t gid)
 100 {
 101         return become_gid(gid) && become_uid(uid);
 102 }
 103
 104 /****************************************************************************
 105  Drop back to root privileges in order to change to another user.
 106 ****************************************************************************/
 107
 108 static void gain_root(void)
 109 {
 110         if (non_root_mode()) {
 111                 return;
 112         }
 113
 114         if (geteuid() != 0) {
 115                 set_effective_uid(0);
 116
 117                 if (geteuid() != 0) {
 118                         DEBUG(0,
 119                               ("Warning: You appear to have a trapdoor "
 120                                "uid system\n"));
 121                 }
 122         }
 123
 124         if (getegid() != 0) {
 125                 set_effective_gid(0);
 126
 127                 if (getegid() != 0) {
 128                         DEBUG(0,
 129                               ("Warning: You appear to have a trapdoor "
 130                                "gid system\n"));
 131                 }
 132         }
 133 }
 134
 135 /****************************************************************************
 136  Get the list of current groups.
 137 ****************************************************************************/
 138
 139 static int get_current_groups(gid_t gid, uint32_t *p_ngroups, gid_t **p_groups)
 140 {
 141         int i;
 142         gid_t grp;
 143         int ngroups;
 144         gid_t *groups = NULL;
 145
 146         (*p_ngroups) = 0;
 147         (*p_groups) = NULL;
 148
 149         /* this looks a little strange, but is needed to cope with
 150            systems that put the current egid in the group list
 151            returned from getgroups() (tridge) */
 152         save_re_gid();
 153         set_effective_gid(gid);
 154         setgid(gid);
 155
 156         ngroups = sys_getgroups(0,&grp);
 157         if (ngroups <= 0) {
 158                 goto fail;
 159         }
 160
 161         if((groups = SMB_MALLOC_ARRAY(gid_t, ngroups+1)) == NULL) {
 162                 DEBUG(0,("setup_groups malloc fail !\n"));
 163                 goto fail;
 164         }
 165
 166         if ((ngroups = sys_getgroups(ngroups,groups)) == -1) {
 167                 goto fail;
 168         }
 169
 170         restore_re_gid();
 171
 172         (*p_ngroups) = ngroups;
 173         (*p_groups) = groups;
 174
 175         DEBUG( 4, ( "get_current_groups: user is in %u groups: ", ngroups));
 176         for (i = 0; i < ngroups; i++ ) {
 177                 DEBUG( 4, ( "%s%d", (i ? ", " : ""), (int)groups[i] ) );
 178         }
 179         DEBUG( 4, ( "\n" ) );
 180
 181         return ngroups;
 182
 183 fail:
 184         SAFE_FREE(groups);
 185         restore_re_gid();
 186         return -1;
 187 }
 188
 189 /****************************************************************************
 190  Create a new security context on the stack.  It is the same as the old
 191  one.  User changes are done using the set_sec_ctx() function.
 192 ****************************************************************************/
 193
 194 bool push_sec_ctx(void)
 195 {
 196         struct sec_ctx *ctx_p;
 197
 198         /* Check we don't overflow our stack */
 199
 200         if (sec_ctx_stack_ndx == MAX_SEC_CTX_DEPTH) {
 201                 DEBUG(0, ("Security context stack overflow!\n"));
 202                 smb_panic("Security context stack overflow!");
 203         }
 204
 205         /* Store previous user context */
 206
 207         sec_ctx_stack_ndx++;
 208
 209         ctx_p = &sec_ctx_stack[sec_ctx_stack_ndx];
 210
 211         ctx_p->ut.uid = geteuid();
 212         ctx_p->ut.gid = getegid();
 213
 214         DEBUG(4, ("push_sec_ctx(%u, %u) : sec_ctx_stack_ndx = %d\n",
 215                   (unsigned int)ctx_p->ut.uid, (unsigned int)ctx_p->ut.gid, sec_ctx_stack_ndx ));
 216
 217         ctx_p->token = dup_nt_token(NULL,
 218                                     sec_ctx_stack[sec_ctx_stack_ndx-1].token);
 219
 220         ctx_p->ut.ngroups = sys_getgroups(0, NULL);
 221
 222         if (ctx_p->ut.ngroups != 0) {
 223                 if (!(ctx_p->ut.groups = SMB_MALLOC_ARRAY(gid_t, ctx_p->ut.ngroups))) {
 224                         DEBUG(0, ("Out of memory in push_sec_ctx()\n"));
 225                         TALLOC_FREE(ctx_p->token);
 226                         return False;
 227                 }
 228
 229                 sys_getgroups(ctx_p->ut.ngroups, ctx_p->ut.groups);
 230         } else {
 231                 ctx_p->ut.groups = NULL;
 232         }
 233
 234         return True;
 235 }
 236
 237 /****************************************************************************
 238  Change UNIX security context. Calls panic if not successful so no return value.
 239 ****************************************************************************/
 240
 241 #ifndef HAVE_DARWIN_INITGROUPS
 242
 243 /* Normal credential switch path. */
 244
 245 static void set_unix_security_ctx(uid_t uid, gid_t gid, int ngroups, gid_t *groups)
 246 {
 247         /* Start context switch */
 248         gain_root();
 249 #ifdef HAVE_SETGROUPS
 250         if (sys_setgroups(gid, ngroups, groups) != 0 && !non_root_mode()) {
 251                 smb_panic("sys_setgroups failed");
 252         }
 253 #endif
 254         become_id(uid, gid);
 255         /* end context switch */
 256 }
 257
 258 #else /* HAVE_DARWIN_INITGROUPS */
 259
 260 /* The Darwin groups implementation is a little unusual. The list of
 261 * groups in the kernel credential is not exhaustive, but more like
 262 * a cache. The full group list is held in userspace and checked
 263 * dynamically.
 264 *
 265 * This is an optional mechanism, and setgroups(2) opts out
 266 * of it. That is, if you call setgroups, then the list of groups you
 267 * set are the only groups that are ever checked. This is not what we
 268 * want. We want to opt in to the dynamic resolution mechanism, so we
 269 * need to specify the uid of the user whose group list (cache) we are
 270 * setting.
 271 *
 272 * The Darwin rules are:
 273 *  1. Thou shalt setegid, initgroups and seteuid IN THAT ORDER
 274 *  2. Thou shalt not pass more that NGROUPS_MAX to initgroups
 275 *  3. Thou shalt leave the first entry in the groups list well alone
 276 */
 277
 278 #include <sys/syscall.h>
 279
 280 static void set_unix_security_ctx(uid_t uid, gid_t gid, int ngroups, gid_t *groups)
 281 {
 282         int max = groups_max();
 283
 284         /* Start context switch */
 285         gain_root();
 286
 287         become_gid(gid);
 288
 289
 290         if (syscall(SYS_initgroups, (ngroups > max) ? max : ngroups,
 291                         groups, uid) == -1 && !non_root_mode()) {
 292                 DEBUG(0, ("WARNING: failed to set group list "
 293                         "(%d groups) for UID %ld: %s\n",
 294                         ngroups, uid, strerror(errno)));
 295                 smb_panic("sys_setgroups failed");
 296         }
 297
 298         become_uid(uid);
 299         /* end context switch */
 300 }
 301
 302 #endif /* HAVE_DARWIN_INITGROUPS */
 303
 304 /****************************************************************************
 305  Set the current security context to a given user.
 306 ****************************************************************************/
 307
 308 void set_sec_ctx(uid_t uid, gid_t gid, int ngroups, gid_t *groups, const struct security_token *token)
 309 {
 310         struct sec_ctx *ctx_p = &sec_ctx_stack[sec_ctx_stack_ndx];
 311
 312         /* Set the security context */
 313
 314         DEBUG(4, ("setting sec ctx (%u, %u) - sec_ctx_stack_ndx = %d\n",
 315                 (unsigned int)uid, (unsigned int)gid, sec_ctx_stack_ndx));
 316
 317         security_token_debug(DBGC_CLASS, 5, token);
 318         debug_unix_user_token(DBGC_CLASS, 5, uid, gid, ngroups, groups);
 319
 320         /* Change uid, gid and supplementary group list. */
 321         set_unix_security_ctx(uid, gid, ngroups, groups);
 322
 323         ctx_p->ut.ngroups = ngroups;
 324
 325         SAFE_FREE(ctx_p->ut.groups);
 326         if (token && (token == ctx_p->token)) {
 327                 smb_panic("DUPLICATE_TOKEN");
 328         }
 329
 330         TALLOC_FREE(ctx_p->token);
 331
 332         if (ngroups) {
 333                 ctx_p->ut.groups = (gid_t *)memdup(groups,
 334                                                    sizeof(gid_t) * ngroups);
 335                 if (!ctx_p->ut.groups) {
 336                         smb_panic("memdup failed");
 337                 }
 338         } else {
 339                 ctx_p->ut.groups = NULL;
 340         }
 341
 342         if (token) {
 343                 ctx_p->token = dup_nt_token(NULL, token);
 344                 if (!ctx_p->token) {
 345                         smb_panic("dup_nt_token failed");
 346                 }
 347         } else {
 348                 ctx_p->token = NULL;
 349         }
 350
 351         ctx_p->ut.uid = uid;
 352         ctx_p->ut.gid = gid;
 353
 354         /* Update current_user stuff */
 355
 356         current_user.ut.uid = uid;
 357         current_user.ut.gid = gid;
 358         current_user.ut.ngroups = ngroups;
 359         current_user.ut.groups = groups;
 360         current_user.nt_user_token = ctx_p->token;
 361 }
 362
 363 /****************************************************************************
 364  Become root context.
 365 ****************************************************************************/
 366
 367 void set_root_sec_ctx(void)
 368 {
 369         /* May need to worry about supplementary groups at some stage */
 370
 371         set_sec_ctx(0, 0, 0, NULL, NULL);
 372 }
 373
 374 /****************************************************************************
 375  Pop a security context from the stack.
 376 ****************************************************************************/
 377
 378 bool pop_sec_ctx(void)
 379 {
 380         struct sec_ctx *ctx_p;
 381         struct sec_ctx *prev_ctx_p;
 382
 383         /* Check for stack underflow */
 384
 385         if (sec_ctx_stack_ndx == 0) {
 386                 DEBUG(0, ("Security context stack underflow!\n"));
 387                 smb_panic("Security context stack underflow!");
 388         }
 389
 390         ctx_p = &sec_ctx_stack[sec_ctx_stack_ndx];
 391
 392         /* Clear previous user info */
 393
 394         ctx_p->ut.uid = (uid_t)-1;
 395         ctx_p->ut.gid = (gid_t)-1;
 396
 397         SAFE_FREE(ctx_p->ut.groups);
 398         ctx_p->ut.ngroups = 0;
 399
 400         TALLOC_FREE(ctx_p->token);
 401
 402         /* Pop back previous user */
 403
 404         sec_ctx_stack_ndx--;
 405
 406         prev_ctx_p = &sec_ctx_stack[sec_ctx_stack_ndx];
 407
 408         /* Change uid, gid and supplementary group list. */
 409         set_unix_security_ctx(prev_ctx_p->ut.uid,
 410                         prev_ctx_p->ut.gid,
 411                         prev_ctx_p->ut.ngroups,
 412                         prev_ctx_p->ut.groups);
 413
 414         /* Update current_user stuff */
 415
 416         current_user.ut.uid = prev_ctx_p->ut.uid;
 417         current_user.ut.gid = prev_ctx_p->ut.gid;
 418         current_user.ut.ngroups = prev_ctx_p->ut.ngroups;
 419         current_user.ut.groups = prev_ctx_p->ut.groups;
 420         current_user.nt_user_token = prev_ctx_p->token;
 421
 422         DEBUG(4, ("pop_sec_ctx (%u, %u) - sec_ctx_stack_ndx = %d\n",
 423                 (unsigned int)geteuid(), (unsigned int)getegid(), sec_ctx_stack_ndx));
 424
 425         return True;
 426 }
 427
 428 /* Initialise the security context system */
 429
 430 void init_sec_ctx(void)
 431 {
 432         int i;
 433         struct sec_ctx *ctx_p;
 434
 435         /* Initialise security context stack */
 436
 437         memset(sec_ctx_stack, 0, sizeof(struct sec_ctx) * MAX_SEC_CTX_DEPTH);
 438
 439         for (i = 0; i < MAX_SEC_CTX_DEPTH; i++) {
 440                 sec_ctx_stack[i].ut.uid = (uid_t)-1;
 441                 sec_ctx_stack[i].ut.gid = (gid_t)-1;
 442         }
 443
 444         /* Initialise first level of stack.  It is the current context */
 445         ctx_p = &sec_ctx_stack[0];
 446
 447         ctx_p->ut.uid = geteuid();
 448         ctx_p->ut.gid = getegid();
 449
 450         get_current_groups(ctx_p->ut.gid, &ctx_p->ut.ngroups, &ctx_p->ut.groups);
 451
 452         ctx_p->token = NULL; /* Maps to guest user. */
 453
 454         /* Initialise current_user global */
 455
 456         current_user.ut.uid = ctx_p->ut.uid;
 457         current_user.ut.gid = ctx_p->ut.gid;
 458         current_user.ut.ngroups = ctx_p->ut.ngroups;
 459         current_user.ut.groups = ctx_p->ut.groups;
 460
 461         /* The conn and vuid are usually taken care of by other modules.
 462            We initialise them here. */
 463
 464         current_user.conn = NULL;
 465         current_user.vuid = UID_FIELD_INVALID;
 466         current_user.nt_user_token = NULL;
 467 }