src/basic/user-util.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2 /***
   3   This file is part of systemd.
   4
   5   Copyright 2010 Lennart Poettering
   6 ***/
   7
   8 #include <alloca.h>
   9 #include <errno.h>
  10 #include <fcntl.h>
  11 #include <grp.h>
  12 #include <pwd.h>
  13 #include <stddef.h>
  14 #include <stdint.h>
  15 #include <stdio.h>
  16 #include <stdlib.h>
  17 #include <string.h>
  18 #include <sys/stat.h>
  19 #include <unistd.h>
  20 #include <utmp.h>
  21
  22 #include "alloc-util.h"
  23 #include "fd-util.h"
  24 #include "fileio.h"
  25 #include "format-util.h"
  26 #include "macro.h"
  27 #include "missing.h"
  28 #include "parse-util.h"
  29 #include "path-util.h"
  30 #include "string-util.h"
  31 #include "strv.h"
  32 #include "user-util.h"
  33 #include "utf8.h"
  34
  35 bool uid_is_valid(uid_t uid) {
  36
  37         /* Also see POSIX IEEE Std 1003.1-2008, 2016 Edition, 3.436. */
  38
  39         /* Some libc APIs use UID_INVALID as special placeholder */
  40         if (uid == (uid_t) UINT32_C(0xFFFFFFFF))
  41                 return false;
  42
  43         /* A long time ago UIDs where 16bit, hence explicitly avoid the 16bit -1 too */
  44         if (uid == (uid_t) UINT32_C(0xFFFF))
  45                 return false;
  46
  47         return true;
  48 }
  49
  50 int parse_uid(const char *s, uid_t *ret) {
  51         uint32_t uid = 0;
  52         int r;
  53
  54         assert(s);
  55
  56         assert_cc(sizeof(uid_t) == sizeof(uint32_t));
  57         r = safe_atou32(s, &uid);
  58         if (r < 0)
  59                 return r;
  60
  61         if (!uid_is_valid(uid))
  62                 return -ENXIO; /* we return ENXIO instead of EINVAL
  63                                 * here, to make it easy to distuingish
  64                                 * invalid numeric uids from invalid
  65                                 * strings. */
  66
  67         if (ret)
  68                 *ret = uid;
  69
  70         return 0;
  71 }
  72
  73 char* getlogname_malloc(void) {
  74         uid_t uid;
  75         struct stat st;
  76
  77         if (isatty(STDIN_FILENO) && fstat(STDIN_FILENO, &st) >= 0)
  78                 uid = st.st_uid;
  79         else
  80                 uid = getuid();
  81
  82         return uid_to_name(uid);
  83 }
  84
  85 char *getusername_malloc(void) {
  86         const char *e;
  87
  88         e = getenv("USER");
  89         if (e)
  90                 return strdup(e);
  91
  92         return uid_to_name(getuid());
  93 }
  94
  95 int get_user_creds(
  96                 const char **username,
  97                 uid_t *uid, gid_t *gid,
  98                 const char **home,
  99                 const char **shell) {
 100
 101         struct passwd *p;
 102         uid_t u;
 103
 104         assert(username);
 105         assert(*username);
 106
 107         /* We enforce some special rules for uid=0 and uid=65534: in order to avoid NSS lookups for root we hardcode
 108          * their user record data. */
 109
 110         if (STR_IN_SET(*username, "root", "0")) {
 111                 *username = "root";
 112
 113                 if (uid)
 114                         *uid = 0;
 115                 if (gid)
 116                         *gid = 0;
 117
 118                 if (home)
 119                         *home = "/root";
 120
 121                 if (shell)
 122                         *shell = "/bin/sh";
 123
 124                 return 0;
 125         }
 126
 127         if (synthesize_nobody() &&
 128             STR_IN_SET(*username, NOBODY_USER_NAME, "65534")) {
 129                 *username = NOBODY_USER_NAME;
 130
 131                 if (uid)
 132                         *uid = UID_NOBODY;
 133                 if (gid)
 134                         *gid = GID_NOBODY;
 135
 136                 if (home)
 137                         *home = "/";
 138
 139                 if (shell)
 140                         *shell = "/sbin/nologin";
 141
 142                 return 0;
 143         }
 144
 145         if (parse_uid(*username, &u) >= 0) {
 146                 errno = 0;
 147                 p = getpwuid(u);
 148
 149                 /* If there are multiple users with the same id, make
 150                  * sure to leave $USER to the configured value instead
 151                  * of the first occurrence in the database. However if
 152                  * the uid was configured by a numeric uid, then let's
 153                  * pick the real username from /etc/passwd. */
 154                 if (p)
 155                         *username = p->pw_name;
 156         } else {
 157                 errno = 0;
 158                 p = getpwnam(*username);
 159         }
 160
 161         if (!p)
 162                 return errno > 0 ? -errno : -ESRCH;
 163
 164         if (uid) {
 165                 if (!uid_is_valid(p->pw_uid))
 166                         return -EBADMSG;
 167
 168                 *uid = p->pw_uid;
 169         }
 170
 171         if (gid) {
 172                 if (!gid_is_valid(p->pw_gid))
 173                         return -EBADMSG;
 174
 175                 *gid = p->pw_gid;
 176         }
 177
 178         if (home)
 179                 *home = p->pw_dir;
 180
 181         if (shell)
 182                 *shell = p->pw_shell;
 183
 184         return 0;
 185 }
 186
 187 static inline bool is_nologin_shell(const char *shell) {
 188
 189         return PATH_IN_SET(shell,
 190                            /* 'nologin' is the friendliest way to disable logins for a user account. It prints a nice
 191                             * message and exits. Different distributions place the binary at different places though,
 192                             * hence let's list them all. */
 193                            "/bin/nologin",
 194                            "/sbin/nologin",
 195                            "/usr/bin/nologin",
 196                            "/usr/sbin/nologin",
 197                            /* 'true' and 'false' work too for the same purpose, but are less friendly as they don't do
 198                             * any message printing. Different distributions place the binary at various places but at
 199                             * least not in the 'sbin' directory. */
 200                            "/bin/false",
 201                            "/usr/bin/false",
 202                            "/bin/true",
 203                            "/usr/bin/true");
 204 }
 205
 206 int get_user_creds_clean(
 207                 const char **username,
 208                 uid_t *uid, gid_t *gid,
 209                 const char **home,
 210                 const char **shell) {
 211
 212         int r;
 213
 214         /* Like get_user_creds(), but resets home/shell to NULL if they don't contain anything relevant. */
 215
 216         r = get_user_creds(username, uid, gid, home, shell);
 217         if (r < 0)
 218                 return r;
 219
 220         if (shell &&
 221             (isempty(*shell) || is_nologin_shell(*shell)))
 222                 *shell = NULL;
 223
 224         if (home && empty_or_root(*home))
 225                 *home = NULL;
 226
 227         return 0;
 228 }
 229
 230 int get_group_creds(const char **groupname, gid_t *gid) {
 231         struct group *g;
 232         gid_t id;
 233
 234         assert(groupname);
 235
 236         /* We enforce some special rules for gid=0: in order to avoid
 237          * NSS lookups for root we hardcode its data. */
 238
 239         if (STR_IN_SET(*groupname, "root", "0")) {
 240                 *groupname = "root";
 241
 242                 if (gid)
 243                         *gid = 0;
 244
 245                 return 0;
 246         }
 247
 248         if (synthesize_nobody() &&
 249             STR_IN_SET(*groupname, NOBODY_GROUP_NAME, "65534")) {
 250                 *groupname = NOBODY_GROUP_NAME;
 251
 252                 if (gid)
 253                         *gid = GID_NOBODY;
 254
 255                 return 0;
 256         }
 257
 258         if (parse_gid(*groupname, &id) >= 0) {
 259                 errno = 0;
 260                 g = getgrgid(id);
 261
 262                 if (g)
 263                         *groupname = g->gr_name;
 264         } else {
 265                 errno = 0;
 266                 g = getgrnam(*groupname);
 267         }
 268
 269         if (!g)
 270                 return errno > 0 ? -errno : -ESRCH;
 271
 272         if (gid) {
 273                 if (!gid_is_valid(g->gr_gid))
 274                         return -EBADMSG;
 275
 276                 *gid = g->gr_gid;
 277         }
 278
 279         return 0;
 280 }
 281
 282 char* uid_to_name(uid_t uid) {
 283         char *ret;
 284         int r;
 285
 286         /* Shortcut things to avoid NSS lookups */
 287         if (uid == 0)
 288                 return strdup("root");
 289         if (synthesize_nobody() &&
 290             uid == UID_NOBODY)
 291                 return strdup(NOBODY_USER_NAME);
 292
 293         if (uid_is_valid(uid)) {
 294                 long bufsize;
 295
 296                 bufsize = sysconf(_SC_GETPW_R_SIZE_MAX);
 297                 if (bufsize <= 0)
 298                         bufsize = 4096;
 299
 300                 for (;;) {
 301                         struct passwd pwbuf, *pw = NULL;
 302                         _cleanup_free_ char *buf = NULL;
 303
 304                         buf = malloc(bufsize);
 305                         if (!buf)
 306                                 return NULL;
 307
 308                         r = getpwuid_r(uid, &pwbuf, buf, (size_t) bufsize, &pw);
 309                         if (r == 0 && pw)
 310                                 return strdup(pw->pw_name);
 311                         if (r != ERANGE)
 312                                 break;
 313
 314                         bufsize *= 2;
 315                 }
 316         }
 317
 318         if (asprintf(&ret, UID_FMT, uid) < 0)
 319                 return NULL;
 320
 321         return ret;
 322 }
 323
 324 char* gid_to_name(gid_t gid) {
 325         char *ret;
 326         int r;
 327
 328         if (gid == 0)
 329                 return strdup("root");
 330         if (synthesize_nobody() &&
 331             gid == GID_NOBODY)
 332                 return strdup(NOBODY_GROUP_NAME);
 333
 334         if (gid_is_valid(gid)) {
 335                 long bufsize;
 336
 337                 bufsize = sysconf(_SC_GETGR_R_SIZE_MAX);
 338                 if (bufsize <= 0)
 339                         bufsize = 4096;
 340
 341                 for (;;) {
 342                         struct group grbuf, *gr = NULL;
 343                         _cleanup_free_ char *buf = NULL;
 344
 345                         buf = malloc(bufsize);
 346                         if (!buf)
 347                                 return NULL;
 348
 349                         r = getgrgid_r(gid, &grbuf, buf, (size_t) bufsize, &gr);
 350                         if (r == 0 && gr)
 351                                 return strdup(gr->gr_name);
 352                         if (r != ERANGE)
 353                                 break;
 354
 355                         bufsize *= 2;
 356                 }
 357         }
 358
 359         if (asprintf(&ret, GID_FMT, gid) < 0)
 360                 return NULL;
 361
 362         return ret;
 363 }
 364
 365 int in_gid(gid_t gid) {
 366         long ngroups_max;
 367         gid_t *gids;
 368         int r, i;
 369
 370         if (getgid() == gid)
 371                 return 1;
 372
 373         if (getegid() == gid)
 374                 return 1;
 375
 376         if (!gid_is_valid(gid))
 377                 return -EINVAL;
 378
 379         ngroups_max = sysconf(_SC_NGROUPS_MAX);
 380         assert(ngroups_max > 0);
 381
 382         gids = newa(gid_t, ngroups_max);
 383
 384         r = getgroups(ngroups_max, gids);
 385         if (r < 0)
 386                 return -errno;
 387
 388         for (i = 0; i < r; i++)
 389                 if (gids[i] == gid)
 390                         return 1;
 391
 392         return 0;
 393 }
 394
 395 int in_group(const char *name) {
 396         int r;
 397         gid_t gid;
 398
 399         r = get_group_creds(&name, &gid);
 400         if (r < 0)
 401                 return r;
 402
 403         return in_gid(gid);
 404 }
 405
 406 int get_home_dir(char **_h) {
 407         struct passwd *p;
 408         const char *e;
 409         char *h;
 410         uid_t u;
 411
 412         assert(_h);
 413
 414         /* Take the user specified one */
 415         e = secure_getenv("HOME");
 416         if (e && path_is_absolute(e)) {
 417                 h = strdup(e);
 418                 if (!h)
 419                         return -ENOMEM;
 420
 421                 *_h = h;
 422                 return 0;
 423         }
 424
 425         /* Hardcode home directory for root and nobody to avoid NSS */
 426         u = getuid();
 427         if (u == 0) {
 428                 h = strdup("/root");
 429                 if (!h)
 430                         return -ENOMEM;
 431
 432                 *_h = h;
 433                 return 0;
 434         }
 435         if (synthesize_nobody() &&
 436             u == UID_NOBODY) {
 437                 h = strdup("/");
 438                 if (!h)
 439                         return -ENOMEM;
 440
 441                 *_h = h;
 442                 return 0;
 443         }
 444
 445         /* Check the database... */
 446         errno = 0;
 447         p = getpwuid(u);
 448         if (!p)
 449                 return errno > 0 ? -errno : -ESRCH;
 450
 451         if (!path_is_absolute(p->pw_dir))
 452                 return -EINVAL;
 453
 454         h = strdup(p->pw_dir);
 455         if (!h)
 456                 return -ENOMEM;
 457
 458         *_h = h;
 459         return 0;
 460 }
 461
 462 int get_shell(char **_s) {
 463         struct passwd *p;
 464         const char *e;
 465         char *s;
 466         uid_t u;
 467
 468         assert(_s);
 469
 470         /* Take the user specified one */
 471         e = getenv("SHELL");
 472         if (e) {
 473                 s = strdup(e);
 474                 if (!s)
 475                         return -ENOMEM;
 476
 477                 *_s = s;
 478                 return 0;
 479         }
 480
 481         /* Hardcode shell for root and nobody to avoid NSS */
 482         u = getuid();
 483         if (u == 0) {
 484                 s = strdup("/bin/sh");
 485                 if (!s)
 486                         return -ENOMEM;
 487
 488                 *_s = s;
 489                 return 0;
 490         }
 491         if (synthesize_nobody() &&
 492             u == UID_NOBODY) {
 493                 s = strdup("/sbin/nologin");
 494                 if (!s)
 495                         return -ENOMEM;
 496
 497                 *_s = s;
 498                 return 0;
 499         }
 500
 501         /* Check the database... */
 502         errno = 0;
 503         p = getpwuid(u);
 504         if (!p)
 505                 return errno > 0 ? -errno : -ESRCH;
 506
 507         if (!path_is_absolute(p->pw_shell))
 508                 return -EINVAL;
 509
 510         s = strdup(p->pw_shell);
 511         if (!s)
 512                 return -ENOMEM;
 513
 514         *_s = s;
 515         return 0;
 516 }
 517
 518 int reset_uid_gid(void) {
 519         int r;
 520
 521         r = maybe_setgroups(0, NULL);
 522         if (r < 0)
 523                 return r;
 524
 525         if (setresgid(0, 0, 0) < 0)
 526                 return -errno;
 527
 528         if (setresuid(0, 0, 0) < 0)
 529                 return -errno;
 530
 531         return 0;
 532 }
 533
 534 int take_etc_passwd_lock(const char *root) {
 535
 536         struct flock flock = {
 537                 .l_type = F_WRLCK,
 538                 .l_whence = SEEK_SET,
 539                 .l_start = 0,
 540                 .l_len = 0,
 541         };
 542
 543         const char *path;
 544         int fd, r;
 545
 546         /* This is roughly the same as lckpwdf(), but not as awful. We
 547          * don't want to use alarm() and signals, hence we implement
 548          * our own trivial version of this.
 549          *
 550          * Note that shadow-utils also takes per-database locks in
 551          * addition to lckpwdf(). However, we don't given that they
 552          * are redundant as they invoke lckpwdf() first and keep
 553          * it during everything they do. The per-database locks are
 554          * awfully racy, and thus we just won't do them. */
 555
 556         if (root)
 557                 path = prefix_roota(root, ETC_PASSWD_LOCK_PATH);
 558         else
 559                 path = ETC_PASSWD_LOCK_PATH;
 560
 561         fd = open(path, O_WRONLY|O_CREAT|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW, 0600);
 562         if (fd < 0)
 563                 return log_debug_errno(errno, "Cannot open %s: %m", path);
 564
 565         r = fcntl(fd, F_SETLKW, &flock);
 566         if (r < 0) {
 567                 safe_close(fd);
 568                 return log_debug_errno(errno, "Locking %s failed: %m", path);
 569         }
 570
 571         return fd;
 572 }
 573
 574 bool valid_user_group_name(const char *u) {
 575         const char *i;
 576         long sz;
 577
 578         /* Checks if the specified name is a valid user/group name. Also see POSIX IEEE Std 1003.1-2008, 2016 Edition,
 579          * 3.437. We are a bit stricter here however. Specifically we deviate from POSIX rules:
 580          *
 581          * - We don't allow any dots (this would break chown syntax which permits dots as user/group name separator)
 582          * - We require that names fit into the appropriate utmp field
 583          * - We don't allow empty user names
 584          *
 585          * Note that other systems are even more restrictive, and don't permit underscores or uppercase characters.
 586          */
 587
 588         if (isempty(u))
 589                 return false;
 590
 591         if (!(u[0] >= 'a' && u[0] <= 'z') &&
 592             !(u[0] >= 'A' && u[0] <= 'Z') &&
 593             u[0] != '_')
 594                 return false;
 595
 596         for (i = u+1; *i; i++) {
 597                 if (!(*i >= 'a' && *i <= 'z') &&
 598                     !(*i >= 'A' && *i <= 'Z') &&
 599                     !(*i >= '0' && *i <= '9') &&
 600                     !IN_SET(*i, '_', '-'))
 601                         return false;
 602         }
 603
 604         sz = sysconf(_SC_LOGIN_NAME_MAX);
 605         assert_se(sz > 0);
 606
 607         if ((size_t) (i-u) > (size_t) sz)
 608                 return false;
 609
 610         if ((size_t) (i-u) > UT_NAMESIZE - 1)
 611                 return false;
 612
 613         return true;
 614 }
 615
 616 bool valid_user_group_name_or_id(const char *u) {
 617
 618         /* Similar as above, but is also fine with numeric UID/GID specifications, as long as they are in the right
 619          * range, and not the invalid user ids. */
 620
 621         if (isempty(u))
 622                 return false;
 623
 624         if (valid_user_group_name(u))
 625                 return true;
 626
 627         return parse_uid(u, NULL) >= 0;
 628 }
 629
 630 bool valid_gecos(const char *d) {
 631
 632         if (!d)
 633                 return false;
 634
 635         if (!utf8_is_valid(d))
 636                 return false;
 637
 638         if (string_has_cc(d, NULL))
 639                 return false;
 640
 641         /* Colons are used as field separators, and hence not OK */
 642         if (strchr(d, ':'))
 643                 return false;
 644
 645         return true;
 646 }
 647
 648 bool valid_home(const char *p) {
 649         /* Note that this function is also called by valid_shell(), any
 650          * changes must account for that. */
 651
 652         if (isempty(p))
 653                 return false;
 654
 655         if (!utf8_is_valid(p))
 656                 return false;
 657
 658         if (string_has_cc(p, NULL))
 659                 return false;
 660
 661         if (!path_is_absolute(p))
 662                 return false;
 663
 664         if (!path_is_normalized(p))
 665                 return false;
 666
 667         /* Colons are used as field separators, and hence not OK */
 668         if (strchr(p, ':'))
 669                 return false;
 670
 671         return true;
 672 }
 673
 674 int maybe_setgroups(size_t size, const gid_t *list) {
 675         int r;
 676
 677         /* Check if setgroups is allowed before we try to drop all the auxiliary groups */
 678         if (size == 0) { /* Dropping all aux groups? */
 679                 _cleanup_free_ char *setgroups_content = NULL;
 680                 bool can_setgroups;
 681
 682                 r = read_one_line_file("/proc/self/setgroups", &setgroups_content);
 683                 if (r == -ENOENT)
 684                         /* Old kernels don't have /proc/self/setgroups, so assume we can use setgroups */
 685                         can_setgroups = true;
 686                 else if (r < 0)
 687                         return r;
 688                 else
 689                         can_setgroups = streq(setgroups_content, "allow");
 690
 691                 if (!can_setgroups) {
 692                         log_debug("Skipping setgroups(), /proc/self/setgroups is set to 'deny'");
 693                         return 0;
 694                 }
 695         }
 696
 697         if (setgroups(size, list) < 0)
 698                 return -errno;
 699
 700         return 0;
 701 }
 702
 703 bool synthesize_nobody(void) {
 704
 705 #ifdef NOLEGACY
 706         return true;
 707 #else
 708         /* Returns true when we shall synthesize the "nobody" user (which we do by default). This can be turned off by
 709          * touching /etc/systemd/dont-synthesize-nobody in order to provide upgrade compatibility with legacy systems
 710          * that used the "nobody" user name and group name for other UIDs/GIDs than 65534.
 711          *
 712          * Note that we do not employ any kind of synchronization on the following caching variable. If the variable is
 713          * accessed in multi-threaded programs in the worst case it might happen that we initialize twice, but that
 714          * shouldn't matter as each initialization should come to the same result. */
 715         static int cache = -1;
 716
 717         if (cache < 0)
 718                 cache = access("/etc/systemd/dont-synthesize-nobody", F_OK) < 0;
 719
 720         return cache;
 721 #endif
 722 }
 723
 724 int putpwent_sane(const struct passwd *pw, FILE *stream) {
 725         assert(pw);
 726         assert(stream);
 727
 728         errno = 0;
 729         if (putpwent(pw, stream) != 0)
 730                 return errno > 0 ? -errno : -EIO;
 731
 732         return 0;
 733 }
 734
 735 int putspent_sane(const struct spwd *sp, FILE *stream) {
 736         assert(sp);
 737         assert(stream);
 738
 739         errno = 0;
 740         if (putspent(sp, stream) != 0)
 741                 return errno > 0 ? -errno : -EIO;
 742
 743         return 0;
 744 }
 745
 746 int putgrent_sane(const struct group *gr, FILE *stream) {
 747         assert(gr);
 748         assert(stream);
 749
 750         errno = 0;
 751         if (putgrent(gr, stream) != 0)
 752                 return errno > 0 ? -errno : -EIO;
 753
 754         return 0;
 755 }
 756
 757 #if ENABLE_GSHADOW
 758 int putsgent_sane(const struct sgrp *sg, FILE *stream) {
 759         assert(sg);
 760         assert(stream);
 761
 762         errno = 0;
 763         if (putsgent(sg, stream) != 0)
 764                 return errno > 0 ? -errno : -EIO;
 765
 766         return 0;
 767 }
 768 #endif
 769
 770 int fgetpwent_sane(FILE *stream, struct passwd **pw) {
 771         struct passwd *p;
 772
 773         assert(pw);
 774         assert(stream);
 775
 776         errno = 0;
 777         p = fgetpwent(stream);
 778         if (!p && errno != ENOENT)
 779                 return errno > 0 ? -errno : -EIO;
 780
 781         *pw = p;
 782         return !!p;
 783 }
 784
 785 int fgetspent_sane(FILE *stream, struct spwd **sp) {
 786         struct spwd *s;
 787
 788         assert(sp);
 789         assert(stream);
 790
 791         errno = 0;
 792         s = fgetspent(stream);
 793         if (!s && errno != ENOENT)
 794                 return errno > 0 ? -errno : -EIO;
 795
 796         *sp = s;
 797         return !!s;
 798 }
 799
 800 int fgetgrent_sane(FILE *stream, struct group **gr) {
 801         struct group *g;
 802
 803         assert(gr);
 804         assert(stream);
 805
 806         errno = 0;
 807         g = fgetgrent(stream);
 808         if (!g && errno != ENOENT)
 809                 return errno > 0 ? -errno : -EIO;
 810
 811         *gr = g;
 812         return !!g;
 813 }
 814
 815 #if ENABLE_GSHADOW
 816 int fgetsgent_sane(FILE *stream, struct sgrp **sg) {
 817         struct sgrp *s;
 818
 819         assert(sg);
 820         assert(stream);
 821
 822         errno = 0;
 823         s = fgetsgent(stream);
 824         if (!s && errno != ENOENT)
 825                 return errno > 0 ? -errno : -EIO;
 826
 827         *sg = s;
 828         return !!s;
 829 }
 830 #endif