*: 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

8 files changed, 208 insertions, 227 deletions

diff --git a/include/libbb.h b/include/libbb.h
index 0b94f70fd..1faa9e9fd 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -1142,9 +1142,16 @@ extern int obscure(const char *old, const char *newval, const struct passwd *pwd
  * (otherwise we risk having same salt generated)
  */
 extern int crypt_make_salt(char *p, int cnt, int rnd) FAST_FUNC;
+
 /* Returns number of lines changed, or -1 on error */
-extern int update_passwd(const char *filename, const char *username,
-                        const char *new_pw) FAST_FUNC;
+#if !(ENABLE_FEATURE_ADDUSER_TO_GROUP || ENABLE_FEATURE_DEL_USER_FROM_GROUP)
+#define update_passwd(filename, username, data, member) \
+        update_passwd(filename, username, data)
+#endif
+extern int update_passwd(const char *filename,
+                const char *username,
+                const char *data,
+                const char *member) FAST_FUNC;
 
 int index_in_str_array(const char *const string_array[], const char *key) FAST_FUNC;
 int index_in_strings(const char *strings, const char *key) FAST_FUNC;
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;
 }
diff --git a/loginutils/addgroup.c b/loginutils/addgroup.c
index 5032d7b99..5a0cf3fff 100644
--- a/loginutils/addgroup.c
+++ b/loginutils/addgroup.c
@@ -9,7 +9,6 @@
  * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
  *
  */
-
 #include "libbb.h"
 
 static void xgroup_study(struct group *g)
@@ -45,8 +44,8 @@ static void xgroup_study(struct group *g)
 /* append a new user to the passwd file */
 static void new_group(char *group, gid_t gid)
 {
-        FILE *file;
         struct group gr;
+        char *p;
 
         /* make sure gid and group haven't already been allocated */
         gr.gr_gid = gid;
@@ -54,67 +53,17 @@ static void new_group(char *group, gid_t gid)
         xgroup_study(&gr);
 
         /* add entry to group */
-        file = xfopen(bb_path_group_file, "a");
-        /* group:passwd:gid:userlist */
-        fprintf(file, "%s:x:%u:\n", group, (unsigned)gr.gr_gid);
+        p = xasprintf("x:%u:", gr.gr_gid);
+        if (update_passwd(bb_path_group_file, group, p, NULL) < 0)
+                exit(EXIT_FAILURE);
         if (ENABLE_FEATURE_CLEAN_UP)
-                fclose(file);
+                free(p);
 #if ENABLE_FEATURE_SHADOWPASSWDS
-        file = fopen_or_warn(bb_path_gshadow_file, "a");
-        if (file) {
-                fprintf(file, "%s:!::\n", group);
-                if (ENABLE_FEATURE_CLEAN_UP)
-                        fclose(file);
-        }
+        /* Ignore errors: if file is missing we suppose admin doesn't want it */
+        update_passwd(bb_path_gshadow_file, group, "!::", NULL);
 #endif
 }
 
-#if ENABLE_FEATURE_ADDUSER_TO_GROUP
-static void add_user_to_group(char **args,
-                const char *path,
-                FILE* FAST_FUNC (*fopen_func)(const char *fileName, const char *mode))
-{
-        char *line;
-        int len = strlen(args[1]);
-        llist_t *plist = NULL;
-        FILE *group_file;
-
-        group_file = fopen_func(path, "r");
-
-        if (!group_file) return;
-
-        while ((line = xmalloc_fgetline(group_file)) != NULL) {
-                /* Find the group */
-                if (!strncmp(line, args[1], len)
-                 && line[len] == ':'
-                ) {
-                        /* Add the new user */
-                        line = xasprintf("%s%s%s", line,
-                                                last_char_is(line, ':') ? "" : ",",
-                                                args[0]);
-                }
-                llist_add_to_end(&plist, line);
-        }
-
-        if (ENABLE_FEATURE_CLEAN_UP) {
-                fclose(group_file);
-                group_file = fopen_func(path, "w");
-                while ((line = llist_pop(&plist))) {
-                        if (group_file)
-                                fprintf(group_file, "%s\n", line);
-                        free(line);
-                }
-                if (group_file)
-                        fclose(group_file);
-        } else {
-                group_file = fopen_func(path, "w");
-                if (group_file)
-                        while ((line = llist_pop(&plist)))
-                                fprintf(group_file, "%s\n", line);
-        }
-}
-#endif
-
 /*
  * addgroup will take a login_name as its first parameter.
  *
@@ -166,10 +115,12 @@ int addgroup_main(int argc UNUSED_PARAM, char **argv)
                                 return EXIT_SUCCESS;
                         }
                 }
-                add_user_to_group(argv, bb_path_group_file, xfopen);
-#if ENABLE_FEATURE_SHADOWPASSWDS
-                add_user_to_group(argv, bb_path_gshadow_file, fopen_or_warn);
-#endif
+                if (update_passwd(bb_path_group_file, argv[1], NULL, argv[0]) < 0) {
+                        return EXIT_FAILURE;
+                }
+# if ENABLE_FEATURE_SHADOWPASSWDS
+                update_passwd(bb_path_gshadow_file, argv[1], NULL, argv[0]);
+# endif
         } else
 #endif /* ENABLE_FEATURE_ADDUSER_TO_GROUP */
         {
diff --git a/loginutils/adduser.c b/loginutils/adduser.c
index b94bb3aea..d0a870c54 100644
--- a/loginutils/adduser.c
+++ b/loginutils/adduser.c
@@ -7,14 +7,12 @@
  *
  * Licensed under the GPL v2 or later, see the file LICENSE in this tarball.
  */
-
 #include "libbb.h"
 
 #define OPT_DONT_SET_PASS  (1 << 4)
 #define OPT_SYSTEM_ACCOUNT (1 << 5)
 #define OPT_DONT_MAKE_HOME (1 << 6)
 
-
 /* remix */
 /* recoded such that the uid may be passed in *p */
 static void passwd_study(struct passwd *p)
@@ -88,10 +86,7 @@ int adduser_main(int argc UNUSED_PARAM, char **argv)
 {
         struct passwd pw;
         const char *usegroup = NULL;
-        FILE *file;
-#if ENABLE_FEATURE_SHADOWPASSWDS
-        int fd;
-#endif
+        char *p;
 
 #if ENABLE_FEATURE_ADDUSER_LONG_OPTIONS
         applet_long_options = adduser_longopts;
@@ -124,32 +119,19 @@ int adduser_main(int argc UNUSED_PARAM, char **argv)
         /* make sure everything is kosher and setup uid && maybe gid */
         passwd_study(&pw);
 
-        /* add to passwd */
-        file = xfopen(bb_path_passwd_file, "a");
-        //fseek(file, 0, SEEK_END); /* paranoia, "a" should ensure that anyway */
-        if (putpwent(&pw, file) != 0) {
-                bb_perror_nomsg_and_die();
+        p = xasprintf("x:%u:%u:%s:%s:%s", pw.pw_uid, pw.pw_gid, pw.pw_gecos, pw.pw_dir, pw.pw_shell);
+        if (update_passwd(bb_path_passwd_file, pw.pw_name, p, NULL) < 0) {
+                return EXIT_FAILURE;
         }
-        /* do fclose even if !ENABLE_FEATURE_CLEAN_UP.
-         * We will exec passwd, files must be flushed & closed before that! */
-        fclose(file);
+        if (ENABLE_FEATURE_CLEAN_UP)
+                free(p);
 
 #if ENABLE_FEATURE_SHADOWPASSWDS
-        /* add to shadow if necessary */
-        /* fopen(..., "a"); would create shadow file, which is wrong.
-         * If shadow file doesn't exist, admin probably does not want it */
-        fd = open_or_warn(bb_path_shadow_file, O_WRONLY | O_APPEND);
-        if (fd >= 0) {
-                char *s = xasprintf("%s:!:%u:0:99999:7:::\n",
-                                pw.pw_name,             /* username */
-                                (unsigned)(time(NULL) / 86400) /* sp->sp_lstchg */
-                                /*0,*/                  /* sp->sp_min */
-                                /*99999,*/              /* sp->sp_max */
-                                /*7*/                   /* sp->sp_warn */
-                );
-                xwrite_str(fd, s);
-                close(fd);
-        }
+        p = xasprintf("!:%u:0:99999:7:::",  (unsigned)(time(NULL) / 86400)); /* sp->sp_lstchg */
+        /* Ignore errors: if file is missing we suppose admin doesn't want it */
+        update_passwd(bb_path_shadow_file, pw.pw_name, p, NULL);
+        if (ENABLE_FEATURE_CLEAN_UP)
+                free(p);
 #endif
 
         /* add to group */
diff --git a/loginutils/chpasswd.c b/loginutils/chpasswd.c
index c83d1dad7..4bffbe83f 100644
--- a/loginutils/chpasswd.c
+++ b/loginutils/chpasswd.c
@@ -5,7 +5,6 @@
  * Written for SLIND (from passwd.c) by Alexander Shishkin <virtuoso@slind.org>
  * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
  */
-
 #include "libbb.h"
 
 #if ENABLE_GETOPT_LONG
@@ -53,10 +52,10 @@ int chpasswd_main(int argc UNUSED_PARAM, char **argv)
                 /* This is rather complex: if user is not found in /etc/shadow,
                  * we try to find & change his passwd in /etc/passwd */
 #if ENABLE_FEATURE_SHADOWPASSWDS
-                rc = update_passwd(bb_path_shadow_file, name, pass);
+                rc = update_passwd(bb_path_shadow_file, name, pass, NULL);
                 if (rc == 0) /* no lines updated, no errors detected */
 #endif
-                        rc = update_passwd(bb_path_passwd_file, name, pass);
+                        rc = update_passwd(bb_path_passwd_file, name, pass, NULL);
                 /* LOGMODE_BOTH logs to syslog also */
                 logmode = LOGMODE_BOTH;
                 if (rc < 0)
diff --git a/loginutils/deluser.c b/loginutils/deluser.c
index 56253712e..293e324b0 100644
--- a/loginutils/deluser.c
+++ b/loginutils/deluser.c
@@ -9,117 +9,48 @@
  * Licensed under GPL version 2, see file LICENSE in this tarball for details.
  *
  */
-
 #include "libbb.h"
 
-/* Status */
-#define STATUS_OK            0
-#define NAME_NOT_FOUND       1
-#define MEMBER_NOT_FOUND     2
-
-static void del_line_matching(char **args,
-                const char *filename,
-                FILE* FAST_FUNC (*fopen_func)(const char *fileName, const char *mode))
+static int del_line_matching(char **args, const char *filename)
 {
-        FILE *passwd;
-        smallint error = NAME_NOT_FOUND;
-        char *name = (ENABLE_FEATURE_DEL_USER_FROM_GROUP && args[2]) ? args[2] : args[1];
-        char *line, *del;
-        char *new = xzalloc(1);
-
-        passwd = fopen_func(filename, "r");
-        if (passwd) {
-                while ((line = xmalloc_fgets(passwd))) {
-                        int len = strlen(name);
-
-                        if (strncmp(line, name, len) == 0
-                         && line[len] == ':'
-                        ) {
-                                error = STATUS_OK;
-                                if (ENABLE_FEATURE_DEL_USER_FROM_GROUP) {
-                                        struct group *gr;
-                                        char *p;
-                                        if (args[2]
-                                         /* There were two args on commandline */
-                                         && (gr = getgrnam(name))
-                                         /* The group was not deleted in the meanwhile */
-                                         && (p = strrchr(line, ':'))
-                                         /* We can find a pointer to the last ':' */
-                                        ) {
-                                                error = MEMBER_NOT_FOUND;
-                                                /* Move past ':' (worst case to '\0') and cut the line */
-                                                p[1] = '\0';
-                                                /* Reuse p */
-                                                for (p = xzalloc(1); *gr->gr_mem != NULL; gr->gr_mem++) {
-                                                        /* Add all the other group members */
-                                                        if (strcmp(args[1], *gr->gr_mem) != 0) {
-                                                                del = p;
-                                                                p = xasprintf("%s%s%s", p, p[0] ? "," : "", *gr->gr_mem);
-                                                                free(del);
-                                                        } else
-                                                                error = STATUS_OK;
-                                                }
-                                                /* Recompose the line */
-                                                line = xasprintf("%s%s\n", line, p);
-                                                if (ENABLE_FEATURE_CLEAN_UP) free(p);
-                                        } else
-                                                goto skip;
-                                }
-                        }
-                        del = new;
-                        new = xasprintf("%s%s", new, line);
-                        free(del);
- skip:
-                        free(line);
-                }
-
-                if (ENABLE_FEATURE_CLEAN_UP) fclose(passwd);
-
-                if (error) {
-                        if (ENABLE_FEATURE_DEL_USER_FROM_GROUP && error == MEMBER_NOT_FOUND) {
-                                /* Set the correct values for error message */
-                                filename = name;
-                                name = args[1];
-                        }
-                        bb_error_msg("can't find %s in %s", name, filename);
-                } else {
-                        passwd = fopen_func(filename, "w");
-                        if (passwd) {
-                                fputs(new, passwd);
-                                if (ENABLE_FEATURE_CLEAN_UP) fclose(passwd);
-                        }
-                }
+        if (ENABLE_FEATURE_DEL_USER_FROM_GROUP && args[2]) {
+                return update_passwd(filename, args[2], NULL, args[1]);
         }
-        free(new);
+        return update_passwd(filename, args[1], NULL, NULL);
 }
 
 int deluser_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int deluser_main(int argc, char **argv)
 {
-        if (argc == 2
-         || (ENABLE_FEATURE_DEL_USER_FROM_GROUP
-            && (applet_name[3] == 'g' && argc == 3))
+        if (argc != 2
+         && (!ENABLE_FEATURE_DEL_USER_FROM_GROUP
+            || (applet_name[3] != 'g' || argc != 3))
         ) {
-                if (geteuid())
-                        bb_error_msg_and_die(bb_msg_perm_denied_are_you_root);
+                bb_show_usage();
+        }
 
-                if ((ENABLE_FEATURE_DEL_USER_FROM_GROUP && argc != 3)
-                 || ENABLE_DELUSER
-                 || (ENABLE_DELGROUP && ENABLE_DESKTOP)
+        if (geteuid())
+                bb_error_msg_and_die(bb_msg_perm_denied_are_you_root);
+
+        if ((ENABLE_FEATURE_DEL_USER_FROM_GROUP && argc != 3)
+         || ENABLE_DELUSER
+         || (ENABLE_DELGROUP && ENABLE_DESKTOP)
+        ) {
+                if (ENABLE_DELUSER
+                 && (!ENABLE_DELGROUP || applet_name[3] == 'u')
                 ) {
-                        if (ENABLE_DELUSER
-                         && (!ENABLE_DELGROUP || applet_name[3] == 'u')
-                        ) {
-                                del_line_matching(argv, bb_path_passwd_file, xfopen);
-                                if (ENABLE_FEATURE_SHADOWPASSWDS)
-                                        del_line_matching(argv, bb_path_shadow_file, fopen_or_warn);
-                        } else if (ENABLE_DESKTOP && ENABLE_DELGROUP && getpwnam(argv[1]))
-                                bb_error_msg_and_die("can't remove primary group of user %s", argv[1]);
-                }
-                del_line_matching(argv, bb_path_group_file, xfopen);
-                if (ENABLE_FEATURE_SHADOWPASSWDS)
-                        del_line_matching(argv, bb_path_gshadow_file, fopen_or_warn);
-                return EXIT_SUCCESS;
-        } else
-                bb_show_usage();
+                        if (del_line_matching(argv, bb_path_passwd_file) < 0)
+                                return EXIT_FAILURE;
+                        if (ENABLE_FEATURE_SHADOWPASSWDS) {
+                                del_line_matching(argv, bb_path_shadow_file);
+                        }
+                } else if (ENABLE_DESKTOP && ENABLE_DELGROUP && getpwnam(argv[1]))
+                        bb_error_msg_and_die("can't remove primary group of user %s", argv[1]);
+        }
+        if (del_line_matching(argv, bb_path_group_file) < 0)
+                return EXIT_FAILURE;
+        if (ENABLE_FEATURE_SHADOWPASSWDS) {
+                del_line_matching(argv, bb_path_gshadow_file);
+        }
+        return EXIT_SUCCESS;
 }
diff --git a/loginutils/passwd.c b/loginutils/passwd.c
index 9ed78c1b7..7b93713b9 100644
--- a/loginutils/passwd.c
+++ b/loginutils/passwd.c
@@ -2,7 +2,6 @@
 /*
  * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
  */
-
 #include "libbb.h"
 #include <syslog.h>
 
@@ -181,12 +180,12 @@ int passwd_main(int argc UNUSED_PARAM, char **argv)
 
 #if ENABLE_FEATURE_SHADOWPASSWDS
         filename = bb_path_shadow_file;
-        rc = update_passwd(bb_path_shadow_file, name, newp);
+        rc = update_passwd(bb_path_shadow_file, name, newp, NULL);
         if (rc == 0) /* no lines updated, no errors detected */
 #endif
         {
                 filename = bb_path_passwd_file;
-                rc = update_passwd(bb_path_passwd_file, name, newp);
+                rc = update_passwd(bb_path_passwd_file, name, newp, NULL);
         }
         /* LOGMODE_BOTH */
         if (rc < 0)