libbb/update_passwd.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * update_passwd
   4  *
   5  * update_passwd is a common function for passwd and chpasswd applets;
   6  * it is responsible for updating password file (i.e. /etc/passwd or
   7  * /etc/shadow) for a given user and password.
   8  *
   9  * Moved from loginutils/passwd.c by Alexander Shishkin <virtuoso@slind.org>
  10  *
  11  * Modified to be able to add or delete users, groups and users to/from groups
  12  * by Tito Ragusa <farmatito@tiscali.it>
  13  *
  14  * Licensed under GPLv2, see file LICENSE in this source tree.
  15  */
  16 #include "libbb.h"
  17
  18 #if ENABLE_SELINUX
  19 static void check_selinux_update_passwd(const char *username)
  20 {
  21         security_context_t context;
  22         char *seuser;
  23
  24         if (getuid() != (uid_t)0 || is_selinux_enabled() == 0)
  25                 return;  /* No need to check */
  26
  27         if (getprevcon_raw(&context) < 0)
  28                 bb_simple_perror_msg_and_die("getprevcon failed");
  29         seuser = strtok(context, ":");
  30         if (!seuser)
  31                 bb_error_msg_and_die("invalid context '%s'", context);
  32         if (strcmp(seuser, username) != 0) {
  33                 security_class_t tclass;
  34                 access_vector_t av;
  35
  36                 tclass = string_to_security_class("passwd");
  37                 if (tclass == 0)
  38                         goto die;
  39                 av = string_to_av_perm(tclass, "passwd");
  40                 if (av == 0)
  41                         goto die;
  42
  43                 if (selinux_check_passwd_access(av) != 0)
  44  die:
  45                         bb_simple_error_msg_and_die("SELinux: access denied");
  46         }
  47         if (ENABLE_FEATURE_CLEAN_UP)
  48                 freecon(context);
  49 }
  50 #else
  51 # define check_selinux_update_passwd(username) ((void)0)
  52 #endif
  53
  54 /*
  55  1) add a user: update_passwd(FILE, USER, REMAINING_PWLINE, NULL)
  56     only if CONFIG_ADDUSER=y and applet_name[0] == 'a' like in adduser
  57
  58  2) add a group: update_passwd(FILE, GROUP, REMAINING_GRLINE, NULL)
  59     only if CONFIG_ADDGROUP=y and applet_name[0] == 'a' like in addgroup
  60
  61  3) add a user to a group: update_passwd(FILE, GROUP, NULL, MEMBER)
  62     only if CONFIG_FEATURE_ADDUSER_TO_GROUP=y, applet_name[0] == 'a'
  63     like in addgroup and member != NULL
  64
  65  4) delete a user: update_passwd(FILE, USER, NULL, NULL)
  66
  67  5) delete a group: update_passwd(FILE, GROUP, NULL, NULL)
  68
  69  6) delete a user from a group: update_passwd(FILE, GROUP, NULL, MEMBER)
  70     only if CONFIG_FEATURE_DEL_USER_FROM_GROUP=y and member != NULL
  71
  72  7) change user's password: update_passwd(FILE, USER, NEW_PASSWD, NULL)
  73     only if CONFIG_PASSWD=y and applet_name[0] == 'p' like in passwd
  74     or if CONFIG_CHPASSWD=y and applet_name[0] == 'c' like in chpasswd
  75
  76  8) delete a user from all groups: update_passwd(FILE, NULL, NULL, MEMBER)
  77
  78  This function does not validate the arguments fed to it
  79  so the calling program should take care of that.
  80
  81  Returns number of lines changed, or -1 on error.
  82 */
  83 int FAST_FUNC update_passwd(const char *filename,
  84                 const char *name,
  85                 const char *new_passwd,
  86                 const char *member)
  87 {
  88 #if !(ENABLE_FEATURE_ADDUSER_TO_GROUP || ENABLE_FEATURE_DEL_USER_FROM_GROUP)
  89 #define member NULL
  90 #endif
  91         struct stat sb;
  92         struct flock lock;
  93         FILE *old_fp;
  94         FILE *new_fp;
  95         char *fnamesfx;
  96         char *sfx_char;
  97         char *name_colon;
  98         int old_fd;
  99         int new_fd;
 100         int i;
 101         int changed_lines;
 102         int ret = -1; /* failure */
 103         /* used as a bool: "are we modifying /etc/shadow?" */
 104 #if ENABLE_FEATURE_SHADOWPASSWDS
 105         const char *shadow = strstr(filename, "shadow");
 106 #else
 107 # define shadow NULL
 108 #endif
 109
 110         filename = xmalloc_follow_symlinks(filename);
 111         if (filename == NULL)
 112                 return ret;
 113
 114         if (name)
 115                 check_selinux_update_passwd(name);
 116
 117         /* New passwd file, "/etc/passwd+" for now */
 118         fnamesfx = xasprintf("%s+", filename);
 119         sfx_char = &fnamesfx[strlen(fnamesfx)-1];
 120         name_colon = xasprintf("%s:", name ? name : "");
 121
 122         if (shadow)
 123                 old_fp = fopen(filename, "r+");
 124         else
 125                 old_fp = fopen_or_warn(filename, "r+");
 126         if (!old_fp) {
 127                 if (shadow)
 128                         ret = 0; /* missing shadow is not an error */
 129                 goto free_mem;
 130         }
 131         old_fd = fileno(old_fp);
 132
 133         selinux_preserve_fcontext(old_fd);
 134
 135         /* Try to create "/etc/passwd+". Wait if it exists. */
 136         i = 30;
 137         do {
 138                 // FIXME: on last iteration try w/o O_EXCL but with O_TRUNC?
 139                 new_fd = open(fnamesfx, O_WRONLY|O_CREAT|O_EXCL, 0600);
 140                 if (new_fd >= 0) goto created;
 141                 if (errno != EEXIST) break;
 142                 usleep(100000); /* 0.1 sec */
 143         } while (--i);
 144         bb_perror_msg("can't create '%s'", fnamesfx);
 145         goto close_old_fp;
 146
 147  created:
 148         if (fstat(old_fd, &sb) == 0) {
 149                 fchmod(new_fd, sb.st_mode & 0777); /* ignore errors */
 150                 fchown(new_fd, sb.st_uid, sb.st_gid);
 151         }
 152         errno = 0;
 153         new_fp = xfdopen_for_write(new_fd);
 154
 155         /* Backup file is "/etc/passwd-" */
 156         *sfx_char = '-';
 157         /* Delete old backup */
 158         i = (unlink(fnamesfx) && errno != ENOENT);
 159         /* Create backup as a hardlink to current */
 160         if (i || link(filename, fnamesfx))
 161                 bb_perror_msg("warning: can't create backup copy '%s'",
 162                                 fnamesfx);
 163         *sfx_char = '+';
 164
 165         /* Lock the password file before updating */
 166         lock.l_type = F_WRLCK;
 167         lock.l_whence = SEEK_SET;
 168         lock.l_start = 0;
 169         lock.l_len = 0;
 170         if (fcntl(old_fd, F_SETLK, &lock) < 0)
 171                 bb_perror_msg("warning: can't lock '%s'", filename);
 172         lock.l_type = F_UNLCK;
 173
 174         /* Read current password file, write updated /etc/passwd+ */
 175         changed_lines = 0;
 176         while (1) {
 177                 char *cp, *line;
 178
 179                 line = xmalloc_fgetline(old_fp);
 180                 if (!line) /* EOF/error */
 181                         break;
 182
 183 #if ENABLE_FEATURE_ADDUSER_TO_GROUP || ENABLE_FEATURE_DEL_USER_FROM_GROUP
 184                 if (!name && member) {
 185                         /* Delete member from all groups */
 186                         /* line is "GROUP:PASSWD:[member1[,member2]...]" */
 187                         unsigned member_len = strlen(member);
 188                         char *list = strrchr(line, ':');
 189                         while (list) {
 190                                 list++;
 191  next_list_element:
 192                                 if (is_prefixed_with(list, member)) {
 193                                         char c;
 194                                         changed_lines++;
 195                                         c = list[member_len];
 196                                         if (c == '\0') {
 197                                                 if (list[-1] == ',')
 198                                                         list--;
 199                                                 *list = '\0';
 200                                                 break;
 201                                         }
 202                                         if (c == ',') {
 203                                                 overlapping_strcpy(list, list + member_len + 1);
 204                                                 goto next_list_element;
 205                                         }
 206                                         changed_lines--;
 207                                 }
 208                                 list = strchr(list, ',');
 209                         }
 210                         fprintf(new_fp, "%s\n", line);
 211                         goto next;
 212                 }
 213 #endif
 214
 215                 cp = is_prefixed_with(line, name_colon);
 216                 if (!cp) {
 217                         fprintf(new_fp, "%s\n", line);
 218                         goto next;
 219                 }
 220
 221                 /* We have a match with "name:"... */
 222                 /* cp points past "name:" */
 223
 224 #if ENABLE_FEATURE_ADDUSER_TO_GROUP || ENABLE_FEATURE_DEL_USER_FROM_GROUP
 225                 if (member) {
 226                         /* It's actually /etc/group+, not /etc/passwd+ */
 227                         if (ENABLE_FEATURE_ADDUSER_TO_GROUP
 228                          && applet_name[0] == 'a'
 229                         ) {
 230                                 /* Add user to group */
 231                                 fprintf(new_fp, "%s%s%s\n", line,
 232                                         last_char_is(line, ':') ? "" : ",",
 233                                         member);
 234                                 changed_lines++;
 235                         } else if (ENABLE_FEATURE_DEL_USER_FROM_GROUP
 236                         /* && applet_name[0] == 'd' */
 237                         ) {
 238                                 /* Delete user from group */
 239                                 char *tmp;
 240                                 const char *fmt = "%s";
 241
 242                                 /* find the start of the member list: last ':' */
 243                                 cp = strrchr(line, ':');
 244                                 /* cut it */
 245                                 *cp++ = '\0';
 246                                 /* write the cut line name:passwd:gid:
 247                                  * or name:!:: */
 248                                 fprintf(new_fp, "%s:", line);
 249                                 /* parse the tokens of the member list */
 250                                 tmp = cp;
 251                                 while ((cp = strsep(&tmp, ",")) != NULL) {
 252                                         if (strcmp(member, cp) != 0) {
 253                                                 fprintf(new_fp, fmt, cp);
 254                                                 fmt = ",%s";
 255                                         } else {
 256                                                 /* found member, skip it */
 257                                                 changed_lines++;
 258                                         }
 259                                 }
 260                                 fprintf(new_fp, "\n");
 261                         }
 262                 } else
 263 #endif
 264                 if ((ENABLE_PASSWD && applet_name[0] == 'p')
 265                  || (ENABLE_CHPASSWD && applet_name[0] == 'c')
 266                 ) {
 267                         /* Change passwd */
 268                         cp = strchrnul(cp, ':'); /* move past old passwd */
 269
 270                         if (shadow && *cp == ':') {
 271                                 /* /etc/shadow's field 3 (passwd change date) needs updating */
 272                                 /* move past old change date */
 273                                 unsigned time_days = (unsigned long)(time(NULL)) / (24*60*60);
 274
 275                                 if (time_days == 0) {
 276                                         /* 0 as change date has special meaning, avoid it */
 277                                         time_days = 1;
 278                                 }
 279                                 cp = strchrnul(cp + 1, ':');
 280                                 /* "name:" + "new_passwd" + ":" + "change date" + ":rest of line" */
 281                                 fprintf(new_fp, "%s%s:%u%s\n", name_colon, new_passwd,
 282                                         time_days, cp);
 283                         } else {
 284                                 /* "name:" + "new_passwd" + ":rest of line" */
 285                                 fprintf(new_fp, "%s%s%s\n", name_colon, new_passwd, cp);
 286                         }
 287                         changed_lines++;
 288                 } /* else delete user or group: skip the line */
 289  next:
 290                 free(line);
 291         }
 292
 293         if (changed_lines == 0) {
 294 #if ENABLE_FEATURE_ADDUSER_TO_GROUP || ENABLE_FEATURE_DEL_USER_FROM_GROUP
 295                 if (member) {
 296                         if (ENABLE_ADDGROUP && applet_name[0] == 'a')
 297                                 bb_error_msg("can't find %s in %s", name, filename);
 298                         if (ENABLE_DELGROUP && applet_name[0] == 'd')
 299                                 bb_error_msg("can't find %s in %s", member, filename);
 300                 }
 301 #endif
 302                 if ((ENABLE_ADDUSER || ENABLE_ADDGROUP)
 303                  && applet_name[0] == 'a' && !member
 304                 ) {
 305                         /* add user or group */
 306                         fprintf(new_fp, "%s%s\n", name_colon, new_passwd);
 307                         changed_lines++;
 308                 }
 309         }
 310
 311         fcntl(old_fd, F_SETLK, &lock);
 312
 313         /* We do want all of them to execute, thus | instead of || */
 314         errno = 0;
 315         if ((ferror(old_fp) | fflush(new_fp) | fsync(new_fd) | fclose(new_fp))
 316          || rename(fnamesfx, filename)
 317         ) {
 318                 /* At least one of those failed */
 319                 bb_perror_nomsg();
 320                 goto unlink_new;
 321         }
 322         /* Success: ret >= 0 */
 323         ret = changed_lines;
 324
 325  unlink_new:
 326         if (ret < 0)
 327                 unlink(fnamesfx);
 328
 329  close_old_fp:
 330         fclose(old_fp);
 331
 332  free_mem:
 333         free(fnamesfx);
 334         free((char *)filename);
 335         free(name_colon);
 336         return ret;
 337 }