*: unify concurrent-safe update of /etc/{passwd,group,[g]shadow}

 by Tito (farmatito AT tiscali.it)

function                                             old     new   delta
update_passwd                                        743    1171    +428
bb_perror_nomsg                                        -       9      +9
find_main                                            436     444      +8
passwd_main                                         1023    1027      +4
nameval                                              202     206      +4
chpasswd_main                                        315     319      +4
bb__parsespent                                       119     117      -2
adduser_main                                         654     650      -4
addgroup_main                                        345     341      -4
sv_main                                             1228    1222      -6
deluser_main                                         173     160     -13
bb_internal_putpwent                                  69       -     -69
add_user_to_group                                    231       -    -231
del_line_matching                                    460      31    -429
------------------------------------------------------------------------------
(add/remove: 1/2 grow/shrink: 5/6 up/down: 457/-758)         Total: -301 bytes

2 files changed, 139 insertions, 27 deletions

diff --git a/libbb/Kbuild b/libbb/Kbuild
index 2c8830f99..57d5d21cf 100644
--- a/libbb/Kbuild
+++ b/libbb/Kbuild
@@ -120,6 +120,9 @@ lib-y += xrealloc_vector.o
 lib-$(CONFIG_FEATURE_MOUNT_LOOP) += loop.o
 lib-$(CONFIG_LOSETUP) += loop.o
 lib-$(CONFIG_FEATURE_MTAB_SUPPORT) += mtab.o
+lib-$(CONFIG_ADDGROUP) += update_passwd.o
+lib-$(CONFIG_ADDUSER) += update_passwd.o
+lib-$(CONFIG_DELUSER) += update_passwd.o
 lib-$(CONFIG_PASSWD) += pw_encrypt.o update_passwd.o
 lib-$(CONFIG_CHPASSWD) += pw_encrypt.o update_passwd.o
 lib-$(CONFIG_CRYPTPW) += pw_encrypt.o
diff --git a/libbb/update_passwd.c b/libbb/update_passwd.c
index 565dd3702..32943482c 100644
--- a/libbb/update_passwd.c
+++ b/libbb/update_passwd.c
@@ -8,9 +8,11 @@
  *
  * Moved from loginutils/passwd.c by Alexander Shishkin <virtuoso@slind.org>
  *
+ * Modified to be able to add or delete users, groups and users to/from groups
+ * by Tito Ragusa <farmatito@tiscali.it>
+ *
  * Licensed under GPLv2, see file LICENSE in this tarball for details.
  */
-
 #include "libbb.h"
 
 #if ENABLE_SELINUX
@@ -35,12 +37,44 @@ static void check_selinux_update_passwd(const char *username)
                 freecon(context);
 }
 #else
-#define check_selinux_update_passwd(username) ((void)0)
+# define check_selinux_update_passwd(username) ((void)0)
 #endif
 
-int FAST_FUNC update_passwd(const char *filename, const char *username,
-                        const char *new_pw)
+/*
+ 1) add a user: update_passwd(FILE, USER, REMAINING_PWLINE, NULL)
+    only if CONFIG_ADDUSER=y and applet_name[0] == 'a' like in adduser
+
+ 2) add a group: update_passwd(FILE, GROUP, REMAINING_GRLINE, NULL)
+    only if CONFIG_ADDGROUP=y and applet_name[0] == 'a' like in addgroup
+
+ 3) add a user to a group: update_passwd(FILE, GROUP, NULL, MEMBER)
+    only if CONFIG_FEATURE_ADDUSER_TO_GROUP=y, applet_name[0] == 'a'
+    like in addgroup and member != NULL
+
+ 4) delete a user: update_passwd(FILE, USER, NULL, NULL)
+
+ 5) delete a group: update_passwd(FILE, GROUP, NULL, NULL)
+
+ 6) delete a user from a group: update_passwd(FILE, GROUP, NULL, MEMBER)
+    only if CONFIG_FEATURE_DEL_USER_FROM_GROUP=y and member != NULL
+
+ 7) change user's passord: update_passwd(FILE, USER, NEW_PASSWD, NULL)
+    only if CONFIG_PASSWD=y and applet_name[0] == 'p' like in passwd
+    or if CONFIG_CHPASSWD=y and applet_name[0] == 'c' like in chpasswd
+
+ This function does not validate the arguments fed to it
+ so the calling program should take care of that.
+
+ Returns number of lines changed, or -1 on error.
+*/
+int FAST_FUNC update_passwd(const char *filename,
+                const char *name,
+                const char *new_passwd,
+                const char *member)
 {
+#if !(ENABLE_FEATURE_ADDUSER_TO_GROUP || ENABLE_FEATURE_DEL_USER_FROM_GROUP)
+#define member NULL
+#endif
         struct stat sb;
         struct flock lock;
         FILE *old_fp;
@@ -51,22 +85,25 @@ int FAST_FUNC update_passwd(const char *filename, const char *username,
         int old_fd;
         int new_fd;
         int i;
-        int cnt = 0;
+        int changed_lines;
         int ret = -1; /* failure */
 
         filename = xmalloc_follow_symlinks(filename);
         if (filename == NULL)
-                return -1;
+                return ret;
 
-        check_selinux_update_passwd(username);
+        check_selinux_update_passwd(name);
 
         /* New passwd file, "/etc/passwd+" for now */
         fnamesfx = xasprintf("%s+", filename);
         sfx_char = &fnamesfx[strlen(fnamesfx)-1];
-        username = xasprintf("%s:", username);
-        user_len = strlen(username);
+        name = xasprintf("%s:", name);
+        user_len = strlen(name);
 
-        old_fp = fopen(filename, "r+");
+        if (strstr(filename, "shadow"))
+                old_fp = fopen(filename, "r+");
+        else
+                old_fp = fopen_or_warn(filename, "r+");
         if (!old_fp)
                 goto free_mem;
         old_fd = fileno(old_fp);
@@ -82,7 +119,7 @@ int FAST_FUNC update_passwd(const char *filename, const char *username,
                 if (errno != EEXIST) break;
                 usleep(100000); /* 0.1 sec */
         } while (--i);
-        bb_perror_msg("cannot create '%s'", fnamesfx);
+        bb_perror_msg("can't create '%s'", fnamesfx);
         goto close_old_fp;
 
  created:
@@ -90,8 +127,10 @@ int FAST_FUNC update_passwd(const char *filename, const char *username,
                 fchmod(new_fd, sb.st_mode & 0777); /* ignore errors */
                 fchown(new_fd, sb.st_uid, sb.st_gid);
         }
+        errno = 0;
         new_fp = fdopen(new_fd, "w");
         if (!new_fp) {
+                bb_perror_nomsg();
                 close(new_fd);
                 goto unlink_new;
         }
@@ -102,7 +141,8 @@ int FAST_FUNC update_passwd(const char *filename, const char *username,
         i = (unlink(fnamesfx) && errno != ENOENT);
         /* Create backup as a hardlink to current */
         if (i || link(filename, fnamesfx))
-                bb_perror_msg("warning: cannot create backup copy '%s'", fnamesfx);
+                bb_perror_msg("warning: can't create backup copy '%s'",
+                                fnamesfx);
         *sfx_char = '+';
 
         /* Lock the password file before updating */
@@ -111,38 +151,107 @@ int FAST_FUNC update_passwd(const char *filename, const char *username,
         lock.l_start = 0;
         lock.l_len = 0;
         if (fcntl(old_fd, F_SETLK, &lock) < 0)
-                bb_perror_msg("warning: cannot lock '%s'", filename);
+                bb_perror_msg("warning: can't lock '%s'", filename);
         lock.l_type = F_UNLCK;
 
         /* Read current password file, write updated /etc/passwd+ */
+        changed_lines = 0;
         while (1) {
-                char *line = xmalloc_fgets(old_fp);
-                if (!line) break; /* EOF/error */
-                if (strncmp(username, line, user_len) == 0) {
-                        /* we have a match with "username:"... */
-                        const char *cp = line + user_len;
-                        /* now cp -> old passwd, skip it: */
-                        cp = strchrnul(cp, ':');
-                        /* now cp -> ':' after old passwd or -> "" */
-                        fprintf(new_fp, "%s%s%s", username, new_pw, cp);
-                        cnt++;
+                char *cp, *line;
+
+                line = xmalloc_fgetline(old_fp);
+                if (!line) /* EOF/error */
+                        break;
+                if (strncmp(name, line, user_len) != 0) {
+                        fprintf(new_fp, "%s\n", line);
+                        goto next;
+                }
+
+                /* We have a match with "name:"... */
+                cp = line + user_len; /* move past name: */
+
+#if ENABLE_FEATURE_ADDUSER_TO_GROUP || ENABLE_FEATURE_DEL_USER_FROM_GROUP
+                if (member) {
+                        /* It's actually /etc/group+, not /etc/passwd+ */
+                        if (ENABLE_FEATURE_ADDUSER_TO_GROUP
+                         && applet_name[0] == 'a'
+                        ) {
+                                /* Add user to group */
+                                fprintf(new_fp, "%s%s%s\n", line,
+                                        last_char_is(line, ':') ? "" : ",",
+                                        member);
+                                changed_lines++;
+                        } else if (ENABLE_FEATURE_DEL_USER_FROM_GROUP
+                        /* && applet_name[0] == 'd' */
+                        ) {
+                                /* Delete user from group */
+                                char *tmp;
+                                const char *fmt = "%s";
+
+                                /* find the start of the member list: last ':' */
+                                cp = strrchr(line, ':');
+                                /* cut it */
+                                *cp++ = '\0';
+                                /* write the cut line name:passwd:gid:
+                                 * or name:!:: */
+                                fprintf(new_fp, "%s:", line);
+                                /* parse the tokens of the member list */
+                                tmp = cp;
+                                while ((cp = strsep(&tmp, ",")) != NULL) {
+                                        if (strcmp(member, cp) != 0) {
+                                                fprintf(new_fp, fmt, cp);
+                                                fmt = ",%s";
+                                        } else {
+                                                /* found member, skip it */
+                                                changed_lines++;
+                                        }
+                                }
+                                fprintf(new_fp, "\n");
+                        }
                 } else
-                        fputs(line, new_fp);
+#endif
+                if ((ENABLE_PASSWD && applet_name[0] == 'p')
+                 || (ENABLE_CHPASSWD && applet_name[0] == 'c')
+                ) {
+                        /* Change passwd */
+                        cp = strchrnul(cp, ':'); /* move past old passwd */
+                        /* name: + new_passwd + :rest of line */
+                        fprintf(new_fp, "%s%s%s\n", name, new_passwd, cp);
+                        changed_lines++;
+                } /* else delete user or group: skip the line */
+ next:
                 free(line);
         }
+
+        if (changed_lines == 0) {
+                if (ENABLE_FEATURE_DEL_USER_FROM_GROUP && member)
+                        bb_error_msg("can't find %s in %s", member, filename);
+                if ((ENABLE_ADDUSER || ENABLE_ADDGROUP)
+                 && applet_name[0] == 'a' && !member
+                ) {
+                        /* add user or group */
+                        fprintf(new_fp, "%s%s\n", name, new_passwd);
+                        changed_lines++;
+                }
+        }
+
         fcntl(old_fd, F_SETLK, &lock);
 
         /* We do want all of them to execute, thus | instead of || */
+        errno = 0;
         if ((ferror(old_fp) | fflush(new_fp) | fsync(new_fd) | fclose(new_fp))
          || rename(fnamesfx, filename)
         ) {
                 /* At least one of those failed */
+                bb_perror_nomsg();
                 goto unlink_new;
         }
-        ret = cnt; /* whee, success! */
+        /* Success: ret >= 0 */
+        ret = changed_lines;
 
  unlink_new:
-        if (ret < 0) unlink(fnamesfx);
+        if (ret < 0)
+                unlink(fnamesfx);
 
  close_old_fp:
         fclose(old_fp);
@@ -150,6 +259,6 @@ int FAST_FUNC update_passwd(const char *filename, const char *username,
  free_mem:
         free(fnamesfx);
         free((char *)filename);
-        free((char *)username);
+        free((char *)name);
         return ret;
 }