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 tarball for details.
  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_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                 if (checkPasswdAccess(PASSWD__PASSWD) != 0)
  34                         bb_error_msg_and_die("SELinux: access denied");
  35         }
  36         if (ENABLE_FEATURE_CLEAN_UP)
  37                 freecon(context);
  38 }
  39 #else
  40 # define check_selinux_update_passwd(username) ((void)0)
  41 #endif
  42
  43 /*
  44  1) add a user: update_passwd(FILE, USER, REMAINING_PWLINE, NULL)
  45     only if CONFIG_ADDUSER=y and applet_name[0] == 'a' like in adduser
  46
  47  2) add a group: update_passwd(FILE, GROUP, REMAINING_GRLINE, NULL)
  48     only if CONFIG_ADDGROUP=y and applet_name[0] == 'a' like in addgroup
  49
  50  3) add a user to a group: update_passwd(FILE, GROUP, NULL, MEMBER)
  51     only if CONFIG_FEATURE_ADDUSER_TO_GROUP=y, applet_name[0] == 'a'
  52     like in addgroup and member != NULL
  53
  54  4) delete a user: update_passwd(FILE, USER, NULL, NULL)
  55
  56  5) delete a group: update_passwd(FILE, GROUP, NULL, NULL)
  57
  58  6) delete a user from a group: update_passwd(FILE, GROUP, NULL, MEMBER)
  59     only if CONFIG_FEATURE_DEL_USER_FROM_GROUP=y and member != NULL
  60
  61  7) change user's passord: update_passwd(FILE, USER, NEW_PASSWD, NULL)
  62     only if CONFIG_PASSWD=y and applet_name[0] == 'p' like in passwd
  63     or if CONFIG_CHPASSWD=y and applet_name[0] == 'c' like in chpasswd
  64
  65  This function does not validate the arguments fed to it
  66  so the calling program should take care of that.
  67
  68  Returns number of lines changed, or -1 on error.
  69 */
  70 int FAST_FUNC update_passwd(const char *filename,
  71                 const char *name,
  72                 const char *new_passwd,
  73                 const char *member)
  74 {
  75 #if !(ENABLE_FEATURE_ADDUSER_TO_GROUP || ENABLE_FEATURE_DEL_USER_FROM_GROUP)
  76 #define member NULL
  77 #endif
  78         struct stat sb;
  79         struct flock lock;
  80         FILE *old_fp;
  81         FILE *new_fp;
  82         char *fnamesfx;
  83         char *sfx_char;
  84         unsigned user_len;
  85         int old_fd;
  86         int new_fd;
  87         int i;
  88         int changed_lines;
  89         int ret = -1; /* failure */
  90         /* used as a bool: "are we modifying /etc/shadow?" */
  91 #if ENABLE_FEATURE_SHADOWPASSWDS
  92         const char *shadow = strstr(filename, "shadow");
  93 #else
  94 # define shadow NULL
  95 #endif
  96
  97         filename = xmalloc_follow_symlinks(filename);
  98         if (filename == NULL)
  99                 return ret;
 100
 101         check_selinux_update_passwd(name);
 102
 103         /* New passwd file, "/etc/passwd+" for now */
 104         fnamesfx = xasprintf("%s+", filename);
 105         sfx_char = &fnamesfx[strlen(fnamesfx)-1];
 106         name = xasprintf("%s:", name);
 107         user_len = strlen(name);
 108
 109         if (shadow)
 110                 old_fp = fopen(filename, "r+");
 111         else
 112                 old_fp = fopen_or_warn(filename, "r+");
 113         if (!old_fp) {
 114                 if (shadow)
 115                         ret = 0; /* missing shadow is not an error */
 116                 goto free_mem;
 117         }
 118         old_fd = fileno(old_fp);
 119
 120         selinux_preserve_fcontext(old_fd);
 121
 122         /* Try to create "/etc/passwd+". Wait if it exists. */
 123         i = 30;
 124         do {
 125                 // FIXME: on last iteration try w/o O_EXCL but with O_TRUNC?
 126                 new_fd = open(fnamesfx, O_WRONLY|O_CREAT|O_EXCL, 0600);
 127                 if (new_fd >= 0) goto created;
 128                 if (errno != EEXIST) break;
 129                 usleep(100000); /* 0.1 sec */
 130         } while (--i);
 131         bb_perror_msg("can't create '%s'", fnamesfx);
 132         goto close_old_fp;
 133
 134  created:
 135         if (!fstat(old_fd, &sb)) {
 136                 fchmod(new_fd, sb.st_mode & 0777); /* ignore errors */
 137                 fchown(new_fd, sb.st_uid, sb.st_gid);
 138         }
 139         errno = 0;
 140         new_fp = xfdopen_for_write(new_fd);
 141
 142         /* Backup file is "/etc/passwd-" */
 143         *sfx_char = '-';
 144         /* Delete old backup */
 145         i = (unlink(fnamesfx) && errno != ENOENT);
 146         /* Create backup as a hardlink to current */
 147         if (i || link(filename, fnamesfx))
 148                 bb_perror_msg("warning: can't create backup copy '%s'",
 149                                 fnamesfx);
 150         *sfx_char = '+';
 151
 152         /* Lock the password file before updating */
 153         lock.l_type = F_WRLCK;
 154         lock.l_whence = SEEK_SET;
 155         lock.l_start = 0;
 156         lock.l_len = 0;
 157         if (fcntl(old_fd, F_SETLK, &lock) < 0)
 158                 bb_perror_msg("warning: can't lock '%s'", filename);
 159         lock.l_type = F_UNLCK;
 160
 161         /* Read current password file, write updated /etc/passwd+ */
 162         changed_lines = 0;
 163         while (1) {
 164                 char *cp, *line;
 165
 166                 line = xmalloc_fgetline(old_fp);
 167                 if (!line) /* EOF/error */
 168                         break;
 169                 if (strncmp(name, line, user_len) != 0) {
 170                         fprintf(new_fp, "%s\n", line);
 171                         goto next;
 172                 }
 173
 174                 /* We have a match with "name:"... */
 175                 cp = line + user_len; /* move past name: */
 176
 177 #if ENABLE_FEATURE_ADDUSER_TO_GROUP || ENABLE_FEATURE_DEL_USER_FROM_GROUP
 178                 if (member) {
 179                         /* It's actually /etc/group+, not /etc/passwd+ */
 180                         if (ENABLE_FEATURE_ADDUSER_TO_GROUP
 181                          && applet_name[0] == 'a'
 182                         ) {
 183                                 /* Add user to group */
 184                                 fprintf(new_fp, "%s%s%s\n", line,
 185                                         last_char_is(line, ':') ? "" : ",",
 186                                         member);
 187                                 changed_lines++;
 188                         } else if (ENABLE_FEATURE_DEL_USER_FROM_GROUP
 189                         /* && applet_name[0] == 'd' */
 190                         ) {
 191                                 /* Delete user from group */
 192                                 char *tmp;
 193                                 const char *fmt = "%s";
 194
 195                                 /* find the start of the member list: last ':' */
 196                                 cp = strrchr(line, ':');
 197                                 /* cut it */
 198                                 *cp++ = '\0';
 199                                 /* write the cut line name:passwd:gid:
 200                                  * or name:!:: */
 201                                 fprintf(new_fp, "%s:", line);
 202                                 /* parse the tokens of the member list */
 203                                 tmp = cp;
 204                                 while ((cp = strsep(&tmp, ",")) != NULL) {
 205                                         if (strcmp(member, cp) != 0) {
 206                                                 fprintf(new_fp, fmt, cp);
 207                                                 fmt = ",%s";
 208                                         } else {
 209                                                 /* found member, skip it */
 210                                                 changed_lines++;
 211                                         }
 212                                 }
 213                                 fprintf(new_fp, "\n");
 214                         }
 215                 } else
 216 #endif
 217                 if ((ENABLE_PASSWD && applet_name[0] == 'p')
 218                  || (ENABLE_CHPASSWD && applet_name[0] == 'c')
 219                 ) {
 220                         /* Change passwd */
 221                         cp = strchrnul(cp, ':'); /* move past old passwd */
 222
 223                         if (shadow && *cp == ':') {
 224                                 /* /etc/shadow's field 3 (passwd change date) needs updating */
 225                                 /* move past old change date */
 226                                 cp = strchrnul(cp + 1, ':');
 227                                 /* "name:" + "new_passwd" + ":" + "change date" + ":rest of line" */
 228                                 fprintf(new_fp, "%s%s:%u%s\n", name, new_passwd,
 229                                         (unsigned)(time(NULL)) / (24*60*60), cp);
 230                         } else {
 231                                 /* "name:" + "new_passwd" + ":rest of line" */
 232                                 fprintf(new_fp, "%s%s%s\n", name, new_passwd, cp);
 233                         }
 234                         changed_lines++;
 235                 } /* else delete user or group: skip the line */
 236  next:
 237                 free(line);
 238         }
 239
 240         if (changed_lines == 0) {
 241 #if ENABLE_FEATURE_DEL_USER_FROM_GROUP
 242                 if (member)
 243                         bb_error_msg("can't find %s in %s", member, filename);
 244 #endif
 245                 if ((ENABLE_ADDUSER || ENABLE_ADDGROUP)
 246                  && applet_name[0] == 'a' && !member
 247                 ) {
 248                         /* add user or group */
 249                         fprintf(new_fp, "%s%s\n", name, new_passwd);
 250                         changed_lines++;
 251                 }
 252         }
 253
 254         fcntl(old_fd, F_SETLK, &lock);
 255
 256         /* We do want all of them to execute, thus | instead of || */
 257         errno = 0;
 258         if ((ferror(old_fp) | fflush(new_fp) | fsync(new_fd) | fclose(new_fp))
 259          || rename(fnamesfx, filename)
 260         ) {
 261                 /* At least one of those failed */
 262                 bb_perror_nomsg();
 263                 goto unlink_new;
 264         }
 265         /* Success: ret >= 0 */
 266         ret = changed_lines;
 267
 268  unlink_new:
 269         if (ret < 0)
 270                 unlink(fnamesfx);
 271
 272  close_old_fp:
 273         fclose(old_fp);
 274
 275  free_mem:
 276         free(fnamesfx);
 277         free((char *)filename);
 278         free((char *)name);
 279         return ret;
 280 }