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         DO_PROFILE_INC(uid_changes);
  70         return True;
  71 }
  72
  73 /****************************************************************************
  74  Become the specified gid.
  75 ****************************************************************************/
  76
  77 static bool become_gid(gid_t gid)
  78 {
  79         /* Check for dodgy gid values */
  80
  81         if (gid == (gid_t)-1 || ((sizeof(gid_t) == 2) &&
  82                                  (gid == (gid_t)65535))) {
  83                 if (!become_gid_done) {
  84                         DEBUG(1,("WARNING: using gid %d is a security risk\n",
  85                                  (int)gid));
  86                         become_gid_done = true;
  87                 }
  88         }
  89
  90         /* Set effective group id */
  91
  92         set_effective_gid(gid);
  93         return True;
  94 }
  95
  96 /****************************************************************************
  97  Become the specified uid and gid.
  98 ****************************************************************************/
  99
 100 static bool become_id(uid_t uid, gid_t gid)
 101 {
 102         return become_gid(gid) && become_uid(uid);
 103 }
 104
 105 /****************************************************************************
 106  Drop back to root privileges in order to change to another user.
 107 ****************************************************************************/
 108
 109 static void gain_root(void)
 110 {
 111         if (non_root_mode()) {
 112                 return;
 113         }
 114
 115         if (geteuid() != 0) {
 116                 set_effective_uid(0);
 117
 118                 if (geteuid() != 0) {
 119                         DEBUG(0,
 120                               ("Warning: You appear to have a trapdoor "
 121                                "uid system\n"));
 122                 }
 123         }
 124
 125         if (getegid() != 0) {
 126                 set_effective_gid(0);
 127
 128                 if (getegid() != 0) {
 129                         DEBUG(0,
 130                               ("Warning: You appear to have a trapdoor "
 131                                "gid system\n"));
 132                 }
 133         }
 134 }
 135
 136 /****************************************************************************
 137  Get the list of current groups.
 138 ****************************************************************************/
 139
 140 static int get_current_groups(gid_t gid, uint32_t *p_ngroups, gid_t **p_groups)
 141 {
 142         int i;
 143         gid_t grp;
 144         int ngroups;
 145         gid_t *groups = NULL;
 146
 147         (*p_ngroups) = 0;
 148         (*p_groups) = NULL;
 149
 150         /* this looks a little strange, but is needed to cope with
 151            systems that put the current egid in the group list
 152            returned from getgroups() (tridge) */
 153         save_re_gid();
 154         set_effective_gid(gid);
 155         samba_setgid(gid);
 156
 157         ngroups = sys_getgroups(0,&grp);
 158         if (ngroups <= 0) {
 159                 goto fail;
 160         }
 161
 162         if((groups = SMB_MALLOC_ARRAY(gid_t, ngroups+1)) == NULL) {
 163                 DEBUG(0,("setup_groups malloc fail !\n"));
 164                 goto fail;
 165         }
 166
 167         if ((ngroups = sys_getgroups(ngroups,groups)) == -1) {
 168                 goto fail;
 169         }
 170
 171         restore_re_gid();
 172
 173         (*p_ngroups) = ngroups;
 174         (*p_groups) = groups;
 175
 176         DEBUG( 4, ( "get_current_groups: user is in %u groups: ", ngroups));
 177         for (i = 0; i < ngroups; i++ ) {
 178                 DEBUG( 4, ( "%s%d", (i ? ", " : ""), (int)groups[i] ) );
 179         }
 180         DEBUG( 4, ( "\n" ) );
 181
 182         return ngroups;
 183
 184 fail:
 185         SAFE_FREE(groups);
 186         restore_re_gid();
 187         return -1;
 188 }
 189
 190 /****************************************************************************
 191  Create a new security context on the stack.  It is the same as the old
 192  one.  User changes are done using the set_sec_ctx() function.
 193 ****************************************************************************/
 194
 195 bool push_sec_ctx(void)
 196 {
 197         struct sec_ctx *ctx_p;
 198
 199         /* Check we don't overflow our stack */
 200
 201         if (sec_ctx_stack_ndx == MAX_SEC_CTX_DEPTH) {
 202                 DEBUG(0, ("Security context stack overflow!\n"));
 203                 smb_panic("Security context stack overflow!");
 204         }
 205
 206         /* Store previous user context */
 207
 208         sec_ctx_stack_ndx++;
 209
 210         ctx_p = &sec_ctx_stack[sec_ctx_stack_ndx];
 211
 212         ctx_p->ut.uid = geteuid();
 213         ctx_p->ut.gid = getegid();
 214
 215         DEBUG(4, ("push_sec_ctx(%u, %u) : sec_ctx_stack_ndx = %d\n",
 216                   (unsigned int)ctx_p->ut.uid, (unsigned int)ctx_p->ut.gid, sec_ctx_stack_ndx ));
 217
 218         ctx_p->token = dup_nt_token(NULL,
 219                                     sec_ctx_stack[sec_ctx_stack_ndx-1].token);
 220
 221         ctx_p->ut.ngroups = sys_getgroups(0, NULL);
 222
 223         if (ctx_p->ut.ngroups != 0) {
 224                 if (!(ctx_p->ut.groups = SMB_MALLOC_ARRAY(gid_t, ctx_p->ut.ngroups))) {
 225                         DEBUG(0, ("Out of memory in push_sec_ctx()\n"));
 226                         TALLOC_FREE(ctx_p->token);
 227                         return False;
 228                 }
 229
 230                 sys_getgroups(ctx_p->ut.ngroups, ctx_p->ut.groups);
 231         } else {
 232                 ctx_p->ut.groups = NULL;
 233         }
 234
 235         return True;
 236 }
 237
 238 /****************************************************************************
 239  Change UNIX security context. Calls panic if not successful so no return value.
 240 ****************************************************************************/
 241
 242 #ifndef HAVE_DARWIN_INITGROUPS
 243
 244 /* Normal credential switch path. */
 245
 246 static void set_unix_security_ctx(uid_t uid, gid_t gid, int ngroups, gid_t *groups)
 247 {
 248         /* Start context switch */
 249         gain_root();
 250 #ifdef HAVE_SETGROUPS
 251         if (sys_setgroups(gid, ngroups, groups) != 0 && !non_root_mode()) {
 252                 smb_panic("sys_setgroups failed");
 253         }
 254 #endif
 255         become_id(uid, gid);
 256         /* end context switch */
 257 }
 258
 259 #else /* HAVE_DARWIN_INITGROUPS */
 260
 261 /* The Darwin groups implementation is a little unusual. The list of
 262 * groups in the kernel credential is not exhaustive, but more like
 263 * a cache. The full group list is held in userspace and checked
 264 * dynamically.
 265 *
 266 * This is an optional mechanism, and setgroups(2) opts out
 267 * of it. That is, if you call setgroups, then the list of groups you
 268 * set are the only groups that are ever checked. This is not what we
 269 * want. We want to opt in to the dynamic resolution mechanism, so we
 270 * need to specify the uid of the user whose group list (cache) we are
 271 * setting.
 272 *
 273 * The Darwin rules are:
 274 *  1. Thou shalt setegid, initgroups and seteuid IN THAT ORDER
 275 *  2. Thou shalt not pass more that NGROUPS_MAX to initgroups
 276 *  3. Thou shalt leave the first entry in the groups list well alone
 277 */
 278
 279 #include <sys/syscall.h>
 280
 281 static void set_unix_security_ctx(uid_t uid, gid_t gid, int ngroups, gid_t *groups)
 282 {
 283         int max = groups_max();
 284
 285         /* Start context switch */
 286         gain_root();
 287
 288         become_gid(gid);
 289
 290
 291         if (syscall(SYS_initgroups, (ngroups > max) ? max : ngroups,
 292                         groups, uid) == -1 && !non_root_mode()) {
 293                 DEBUG(0, ("WARNING: failed to set group list "
 294                         "(%d groups) for UID %d: %s\n",
 295                         ngroups, uid, strerror(errno)));
 296                 smb_panic("sys_setgroups failed");
 297         }
 298
 299         become_uid(uid);
 300         /* end context switch */
 301 }
 302
 303 #endif /* HAVE_DARWIN_INITGROUPS */
 304
 305 /****************************************************************************
 306  Set the current security context to a given user.
 307 ****************************************************************************/
 308
 309 void set_sec_ctx(uid_t uid, gid_t gid, int ngroups, gid_t *groups, const struct security_token *token)
 310 {
 311         struct sec_ctx *ctx_p = &sec_ctx_stack[sec_ctx_stack_ndx];
 312
 313         /* Set the security context */
 314
 315         DEBUG(4, ("setting sec ctx (%u, %u) - sec_ctx_stack_ndx = %d\n",
 316                 (unsigned int)uid, (unsigned int)gid, sec_ctx_stack_ndx));
 317
 318         security_token_debug(DBGC_CLASS, 5, token);
 319         debug_unix_user_token(DBGC_CLASS, 5, uid, gid, ngroups, groups);
 320
 321         /* Change uid, gid and supplementary group list. */
 322         set_unix_security_ctx(uid, gid, ngroups, groups);
 323
 324         ctx_p->ut.ngroups = ngroups;
 325
 326         SAFE_FREE(ctx_p->ut.groups);
 327         if (token && (token == ctx_p->token)) {
 328                 smb_panic("DUPLICATE_TOKEN");
 329         }
 330
 331         TALLOC_FREE(ctx_p->token);
 332
 333         if (ngroups) {
 334                 ctx_p->ut.groups = (gid_t *)memdup(groups,
 335                                                    sizeof(gid_t) * ngroups);
 336                 if (!ctx_p->ut.groups) {
 337                         smb_panic("memdup failed");
 338                 }
 339         } else {
 340                 ctx_p->ut.groups = NULL;
 341         }
 342
 343         if (token) {
 344                 ctx_p->token = dup_nt_token(NULL, token);
 345                 if (!ctx_p->token) {
 346                         smb_panic("dup_nt_token failed");
 347                 }
 348         } else {
 349                 ctx_p->token = NULL;
 350         }
 351
 352         ctx_p->ut.uid = uid;
 353         ctx_p->ut.gid = gid;
 354
 355         /* Update current_user stuff */
 356
 357         current_user.ut.uid = uid;
 358         current_user.ut.gid = gid;
 359         current_user.ut.ngroups = ngroups;
 360         current_user.ut.groups = groups;
 361         current_user.nt_user_token = ctx_p->token;
 362 }
 363
 364 /****************************************************************************
 365  Become root context.
 366 ****************************************************************************/
 367
 368 void set_root_sec_ctx(void)
 369 {
 370         /* May need to worry about supplementary groups at some stage */
 371
 372         set_sec_ctx(0, 0, 0, NULL, NULL);
 373 }
 374
 375 /****************************************************************************
 376  Pop a security context from the stack.
 377 ****************************************************************************/
 378
 379 bool pop_sec_ctx(void)
 380 {
 381         struct sec_ctx *ctx_p;
 382         struct sec_ctx *prev_ctx_p;
 383
 384         /* Check for stack underflow */
 385
 386         if (sec_ctx_stack_ndx == 0) {
 387                 DEBUG(0, ("Security context stack underflow!\n"));
 388                 smb_panic("Security context stack underflow!");
 389         }
 390
 391         ctx_p = &sec_ctx_stack[sec_ctx_stack_ndx];
 392
 393         /* Clear previous user info */
 394
 395         ctx_p->ut.uid = (uid_t)-1;
 396         ctx_p->ut.gid = (gid_t)-1;
 397
 398         SAFE_FREE(ctx_p->ut.groups);
 399         ctx_p->ut.ngroups = 0;
 400
 401         TALLOC_FREE(ctx_p->token);
 402
 403         /* Pop back previous user */
 404
 405         sec_ctx_stack_ndx--;
 406
 407         prev_ctx_p = &sec_ctx_stack[sec_ctx_stack_ndx];
 408
 409         /* Change uid, gid and supplementary group list. */
 410         set_unix_security_ctx(prev_ctx_p->ut.uid,
 411                         prev_ctx_p->ut.gid,
 412                         prev_ctx_p->ut.ngroups,
 413                         prev_ctx_p->ut.groups);
 414
 415         /* Update current_user stuff */
 416
 417         current_user.ut.uid = prev_ctx_p->ut.uid;
 418         current_user.ut.gid = prev_ctx_p->ut.gid;
 419         current_user.ut.ngroups = prev_ctx_p->ut.ngroups;
 420         current_user.ut.groups = prev_ctx_p->ut.groups;
 421         current_user.nt_user_token = prev_ctx_p->token;
 422
 423         DEBUG(4, ("pop_sec_ctx (%u, %u) - sec_ctx_stack_ndx = %d\n",
 424                 (unsigned int)geteuid(), (unsigned int)getegid(), sec_ctx_stack_ndx));
 425
 426         return True;
 427 }
 428
 429 /* Initialise the security context system */
 430
 431 void init_sec_ctx(void)
 432 {
 433         int i;
 434         struct sec_ctx *ctx_p;
 435
 436         /* Initialise security context stack */
 437
 438         memset(sec_ctx_stack, 0, sizeof(struct sec_ctx) * MAX_SEC_CTX_DEPTH);
 439
 440         for (i = 0; i < MAX_SEC_CTX_DEPTH; i++) {
 441                 sec_ctx_stack[i].ut.uid = (uid_t)-1;
 442                 sec_ctx_stack[i].ut.gid = (gid_t)-1;
 443         }
 444
 445         /* Initialise first level of stack.  It is the current context */
 446         ctx_p = &sec_ctx_stack[0];
 447
 448         ctx_p->ut.uid = geteuid();
 449         ctx_p->ut.gid = getegid();
 450
 451         get_current_groups(ctx_p->ut.gid, &ctx_p->ut.ngroups, &ctx_p->ut.groups);
 452
 453         ctx_p->token = NULL; /* Maps to guest user. */
 454
 455         /* Initialise current_user global */
 456
 457         current_user.ut.uid = ctx_p->ut.uid;
 458         current_user.ut.gid = ctx_p->ut.gid;
 459         current_user.ut.ngroups = ctx_p->ut.ngroups;
 460         current_user.ut.groups = ctx_p->ut.groups;
 461
 462         /* The conn and vuid are usually taken care of by other modules.
 463            We initialise them here. */
 464
 465         current_user.conn = NULL;
 466         current_user.vuid = UID_FIELD_INVALID;
 467         current_user.nt_user_token = NULL;
 468 }
 469
 470 /*************************************************************
 471  Called when we're inside a become_root() temporary escalation
 472  of privileges and the nt_user_token is NULL. Return the last
 473  active token on the context stack. We know there is at least
 474  one valid non-NULL token on the stack so panic if we underflow.
 475 *************************************************************/
 476
 477 const struct security_token *sec_ctx_active_token(void)
 478 {
 479         int stack_index = sec_ctx_stack_ndx;
 480         struct sec_ctx *ctx_p = &sec_ctx_stack[stack_index];
 481
 482         while (ctx_p->token == NULL) {
 483                 stack_index--;
 484                 if (stack_index < 0) {
 485                         DEBUG(0, ("Security context active token "
 486                                   "stack underflow!\n"));
 487                         smb_panic("Security context active token "
 488                                   "stack underflow!");
 489                 }
 490                 ctx_p = &sec_ctx_stack[stack_index];
 491         }
 492         return ctx_p->token;
 493 }