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 #include "../lib/util/setid.h"
  28
  29 extern struct current_user current_user;
  30
  31 /****************************************************************************
  32  Are two UNIX tokens equal ?
  33 ****************************************************************************/
  34
  35 bool unix_token_equal(const struct security_unix_token *t1, const struct security_unix_token *t2)
  36 {
  37         if (t1->uid != t2->uid || t1->gid != t2->gid ||
  38                         t1->ngroups != t2->ngroups) {
  39                 return false;
  40         }
  41         if (memcmp(t1->groups, t2->groups,
  42                         t1->ngroups*sizeof(gid_t)) != 0) {
  43                 return false;
  44         }
  45         return true;
  46 }
  47
  48 /****************************************************************************
  49  Become the specified uid.
  50 ****************************************************************************/
  51
  52 static bool become_uid(uid_t uid)
  53 {
  54         /* Check for dodgy uid values */
  55
  56         if (uid == (uid_t)-1 ||
  57             ((sizeof(uid_t) == 2) && (uid == (uid_t)65535))) {
  58                 if (!become_uid_done) {
  59                         DEBUG(1,("WARNING: using uid %d is a security risk\n",
  60                                  (int)uid));
  61                         become_uid_done = true;
  62                 }
  63         }
  64
  65         /* Set effective user id */
  66
  67         set_effective_uid(uid);
  68
  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         samba_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         START_PROFILE(push_sec_ctx);
 199
 200         /* Check we don't overflow our stack */
 201
 202         if (sec_ctx_stack_ndx == MAX_SEC_CTX_DEPTH) {
 203                 DEBUG(0, ("Security context stack overflow!\n"));
 204                 smb_panic("Security context stack overflow!");
 205         }
 206
 207         /* Store previous user context */
 208
 209         sec_ctx_stack_ndx++;
 210
 211         ctx_p = &sec_ctx_stack[sec_ctx_stack_ndx];
 212
 213         ctx_p->ut.uid = geteuid();
 214         ctx_p->ut.gid = getegid();
 215
 216         DEBUG(4, ("push_sec_ctx(%u, %u) : sec_ctx_stack_ndx = %d\n",
 217                   (unsigned int)ctx_p->ut.uid, (unsigned int)ctx_p->ut.gid, sec_ctx_stack_ndx ));
 218
 219         ctx_p->token = dup_nt_token(NULL,
 220                                     sec_ctx_stack[sec_ctx_stack_ndx-1].token);
 221
 222         ctx_p->ut.ngroups = sys_getgroups(0, NULL);
 223
 224         if (ctx_p->ut.ngroups != 0) {
 225                 if (!(ctx_p->ut.groups = SMB_MALLOC_ARRAY(gid_t, ctx_p->ut.ngroups))) {
 226                         DEBUG(0, ("Out of memory in push_sec_ctx()\n"));
 227                         TALLOC_FREE(ctx_p->token);
 228                         return False;
 229                 }
 230
 231                 sys_getgroups(ctx_p->ut.ngroups, ctx_p->ut.groups);
 232         } else {
 233                 ctx_p->ut.groups = NULL;
 234         }
 235
 236         END_PROFILE(push_sec_ctx);
 237
 238         return True;
 239 }
 240
 241 /****************************************************************************
 242  Change UNIX security context. Calls panic if not successful so no return value.
 243 ****************************************************************************/
 244
 245 #ifndef HAVE_DARWIN_INITGROUPS
 246
 247 /* Normal credential switch path. */
 248
 249 static void set_unix_security_ctx(uid_t uid, gid_t gid, int ngroups, gid_t *groups)
 250 {
 251         /* Start context switch */
 252         gain_root();
 253 #ifdef HAVE_SETGROUPS
 254         if (sys_setgroups(gid, ngroups, groups) != 0 && !non_root_mode()) {
 255                 smb_panic("sys_setgroups failed");
 256         }
 257 #endif
 258         become_id(uid, gid);
 259         /* end context switch */
 260 }
 261
 262 #else /* HAVE_DARWIN_INITGROUPS */
 263
 264 /* The Darwin groups implementation is a little unusual. The list of
 265 * groups in the kernel credential is not exhaustive, but more like
 266 * a cache. The full group list is held in userspace and checked
 267 * dynamically.
 268 *
 269 * This is an optional mechanism, and setgroups(2) opts out
 270 * of it. That is, if you call setgroups, then the list of groups you
 271 * set are the only groups that are ever checked. This is not what we
 272 * want. We want to opt in to the dynamic resolution mechanism, so we
 273 * need to specify the uid of the user whose group list (cache) we are
 274 * setting.
 275 *
 276 * The Darwin rules are:
 277 *  1. Thou shalt setegid, initgroups and seteuid IN THAT ORDER
 278 *  2. Thou shalt not pass more that NGROUPS_MAX to initgroups
 279 *  3. Thou shalt leave the first entry in the groups list well alone
 280 */
 281
 282 #include <sys/syscall.h>
 283
 284 static void set_unix_security_ctx(uid_t uid, gid_t gid, int ngroups, gid_t *groups)
 285 {
 286         int max = groups_max();
 287
 288         /* Start context switch */
 289         gain_root();
 290
 291         become_gid(gid);
 292
 293
 294         if (syscall(SYS_initgroups, (ngroups > max) ? max : ngroups,
 295                         groups, uid) == -1 && !non_root_mode()) {
 296                 DEBUG(0, ("WARNING: failed to set group list "
 297                         "(%d groups) for UID %d: %s\n",
 298                         ngroups, uid, strerror(errno)));
 299                 smb_panic("sys_setgroups failed");
 300         }
 301
 302         become_uid(uid);
 303         /* end context switch */
 304 }
 305
 306 #endif /* HAVE_DARWIN_INITGROUPS */
 307
 308 /****************************************************************************
 309  Set the current security context to a given user.
 310 ****************************************************************************/
 311
 312 static void set_sec_ctx_internal(uid_t uid, gid_t gid,
 313                                  int ngroups, gid_t *groups,
 314                                  const struct security_token *token)
 315 {
 316         struct sec_ctx *ctx_p = &sec_ctx_stack[sec_ctx_stack_ndx];
 317
 318         /* Set the security context */
 319
 320         DEBUG(4, ("setting sec ctx (%u, %u) - sec_ctx_stack_ndx = %d\n",
 321                 (unsigned int)uid, (unsigned int)gid, sec_ctx_stack_ndx));
 322
 323         security_token_debug(DBGC_CLASS, 5, token);
 324         debug_unix_user_token(DBGC_CLASS, 5, uid, gid, ngroups, groups);
 325
 326         /* Change uid, gid and supplementary group list. */
 327         set_unix_security_ctx(uid, gid, ngroups, groups);
 328
 329         ctx_p->ut.ngroups = ngroups;
 330
 331         SAFE_FREE(ctx_p->ut.groups);
 332         if (token && (token == ctx_p->token)) {
 333                 smb_panic("DUPLICATE_TOKEN");
 334         }
 335
 336         TALLOC_FREE(ctx_p->token);
 337
 338         if (ngroups) {
 339                 ctx_p->ut.groups = (gid_t *)smb_xmemdup(groups,
 340                                                         sizeof(gid_t) * ngroups);
 341         } else {
 342                 ctx_p->ut.groups = NULL;
 343         }
 344
 345         if (token) {
 346                 ctx_p->token = dup_nt_token(NULL, token);
 347                 if (!ctx_p->token) {
 348                         smb_panic("dup_nt_token failed");
 349                 }
 350         } else {
 351                 ctx_p->token = NULL;
 352         }
 353
 354         ctx_p->ut.uid = uid;
 355         ctx_p->ut.gid = gid;
 356
 357         /* Update current_user stuff */
 358
 359         current_user.ut.uid = uid;
 360         current_user.ut.gid = gid;
 361         current_user.ut.ngroups = ngroups;
 362         current_user.ut.groups = groups;
 363         current_user.nt_user_token = ctx_p->token;
 364 }
 365
 366 void set_sec_ctx(uid_t uid, gid_t gid, int ngroups, gid_t *groups, const struct security_token *token)
 367 {
 368         START_PROFILE(set_sec_ctx);
 369         set_sec_ctx_internal(uid, gid, ngroups, groups, token);
 370         END_PROFILE(set_sec_ctx);
 371 }
 372
 373 /****************************************************************************
 374  Become root context.
 375 ****************************************************************************/
 376
 377 void set_root_sec_ctx(void)
 378 {
 379         /* May need to worry about supplementary groups at some stage */
 380
 381         START_PROFILE(set_root_sec_ctx);
 382         set_sec_ctx_internal(0, 0, 0, NULL, NULL);
 383         END_PROFILE(set_root_sec_ctx);
 384 }
 385
 386 /****************************************************************************
 387  Pop a security context from the stack.
 388 ****************************************************************************/
 389
 390 bool pop_sec_ctx(void)
 391 {
 392         struct sec_ctx *ctx_p;
 393         struct sec_ctx *prev_ctx_p;
 394
 395         START_PROFILE(pop_sec_ctx);
 396
 397         /* Check for stack underflow */
 398
 399         if (sec_ctx_stack_ndx == 0) {
 400                 DEBUG(0, ("Security context stack underflow!\n"));
 401                 smb_panic("Security context stack underflow!");
 402         }
 403
 404         ctx_p = &sec_ctx_stack[sec_ctx_stack_ndx];
 405
 406         /* Clear previous user info */
 407
 408         ctx_p->ut.uid = (uid_t)-1;
 409         ctx_p->ut.gid = (gid_t)-1;
 410
 411         SAFE_FREE(ctx_p->ut.groups);
 412         ctx_p->ut.ngroups = 0;
 413
 414         TALLOC_FREE(ctx_p->token);
 415
 416         /* Pop back previous user */
 417
 418         sec_ctx_stack_ndx--;
 419
 420         prev_ctx_p = &sec_ctx_stack[sec_ctx_stack_ndx];
 421
 422         /* Change uid, gid and supplementary group list. */
 423         set_unix_security_ctx(prev_ctx_p->ut.uid,
 424                         prev_ctx_p->ut.gid,
 425                         prev_ctx_p->ut.ngroups,
 426                         prev_ctx_p->ut.groups);
 427
 428         /* Update current_user stuff */
 429
 430         current_user.ut.uid = prev_ctx_p->ut.uid;
 431         current_user.ut.gid = prev_ctx_p->ut.gid;
 432         current_user.ut.ngroups = prev_ctx_p->ut.ngroups;
 433         current_user.ut.groups = prev_ctx_p->ut.groups;
 434         current_user.nt_user_token = prev_ctx_p->token;
 435
 436         END_PROFILE(pop_sec_ctx);
 437
 438         DEBUG(4, ("pop_sec_ctx (%u, %u) - sec_ctx_stack_ndx = %d\n",
 439                 (unsigned int)geteuid(), (unsigned int)getegid(), sec_ctx_stack_ndx));
 440
 441         return True;
 442 }
 443
 444 /* Initialise the security context system */
 445
 446 void init_sec_ctx(void)
 447 {
 448         int i;
 449         struct sec_ctx *ctx_p;
 450
 451         /* Initialise security context stack */
 452
 453         memset(sec_ctx_stack, 0, sizeof(struct sec_ctx) * MAX_SEC_CTX_DEPTH);
 454
 455         for (i = 0; i < MAX_SEC_CTX_DEPTH; i++) {
 456                 sec_ctx_stack[i].ut.uid = (uid_t)-1;
 457                 sec_ctx_stack[i].ut.gid = (gid_t)-1;
 458         }
 459
 460         /* Initialise first level of stack.  It is the current context */
 461         ctx_p = &sec_ctx_stack[0];
 462
 463         ctx_p->ut.uid = geteuid();
 464         ctx_p->ut.gid = getegid();
 465
 466         get_current_groups(ctx_p->ut.gid, &ctx_p->ut.ngroups, &ctx_p->ut.groups);
 467
 468         ctx_p->token = NULL; /* Maps to guest user. */
 469
 470         /* Initialise current_user global */
 471
 472         current_user.ut.uid = ctx_p->ut.uid;
 473         current_user.ut.gid = ctx_p->ut.gid;
 474         current_user.ut.ngroups = ctx_p->ut.ngroups;
 475         current_user.ut.groups = ctx_p->ut.groups;
 476
 477         /* The conn and vuid are usually taken care of by other modules.
 478            We initialise them here. */
 479
 480         current_user.conn = NULL;
 481         current_user.vuid = UID_FIELD_INVALID;
 482         current_user.nt_user_token = NULL;
 483 }
 484
 485 /*************************************************************
 486  Called when we're inside a become_root() temporary escalation
 487  of privileges and the nt_user_token is NULL. Return the last
 488  active token on the context stack. We know there is at least
 489  one valid non-NULL token on the stack so panic if we underflow.
 490 *************************************************************/
 491
 492 const struct security_token *sec_ctx_active_token(void)
 493 {
 494         int stack_index = sec_ctx_stack_ndx;
 495         struct sec_ctx *ctx_p = &sec_ctx_stack[stack_index];
 496
 497         while (ctx_p->token == NULL) {
 498                 stack_index--;
 499                 if (stack_index < 0) {
 500                         DEBUG(0, ("Security context active token "
 501                                   "stack underflow!\n"));
 502                         smb_panic("Security context active token "
 503                                   "stack underflow!");
 504                 }
 505                 ctx_p = &sec_ctx_stack[stack_index];
 506         }
 507         return ctx_p->token;
 508 }