LXR busybox/libbb/update

   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
  19static 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                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_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*/
  83int 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}
 338