From 6e7a2fb6d52fc93f2d964baf6da20bb733917f3a Mon Sep 17 00:00:00 2001
From: Joachim Wiberg <troglobit@gmail.com>
Date: Wed, 13 Sep 2023 11:37:15 +0200
Subject: [PATCH] Fix #357: allow sulogin with user different from 'root'

In issue #357 there's a proposal for optionally allowing /bin/login, but
after intense discussions we've agreed that would be opening up for all
sorts of potential (security) issues.

it's better to keep things as-is but with the added twist of supporting
a custom user at configure time, e.g., 'admin'.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>
---
 configure.ac  | 13 +++++++++----
 src/sulogin.c | 12 +++++++++---
 2 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/configure.ac b/configure.ac
index 99e21fe8..303ea224 100644
--- a/configure.ac
+++ b/configure.ac
@@ -145,10 +145,10 @@ AC_ARG_WITH(keventd,
         AS_HELP_STRING([--with-keventd], [Enable built-in keventd, default: no]),, [with_keventd=no])
 
 AC_ARG_WITH(sulogin,
-        AS_HELP_STRING([--with-sulogin], [Enable built-in sulogin, default: no.]),, [with_sulogin=no])
+        AS_HELP_STRING([--with-sulogin@<:@=USER@:>@], [Enable built-in sulogin, optional USER to request password for (default root), default: no.]),[sulogin=$withval],[with_sulogin=no])
 
 AC_ARG_WITH(watchdog,
-        AS_HELP_STRING([--with-watchdog=[DEV]], [Enable built-in watchdog, default: /dev/watchdog]),
+        AS_HELP_STRING([--with-watchdog@<:@=DEV@:>@], [Enable built-in watchdog, default: /dev/watchdog]),
 	[watchdog=$withval], [with_watchdog=no watchdog=])
 
 AC_ARG_WITH(hook-scripts-path,
@@ -252,7 +252,12 @@ AS_IF([test "x$rtc_date" != "xno"], [
 
 AS_IF([test "x$with_keventd" != "xno"], [with_keventd=yes])
 
-AS_IF([test "x$with_sulogin" != "xno"], [with_sulogin=yes])
+AS_IF([test "x$with_sulogin" != "xno"], [
+	AS_IF([test "x$sulogin" = "xyes"], [
+		sulogin=root])
+	with_sulogin=yes
+        AC_DEFINE_UNQUOTED(SULOGIN_USER, "$sulogin", [Built-in sulogin user, default: root])], [
+	sulogin=])
 
 AS_IF([test "x$with_watchdog" != "xno"], [
 	AS_IF([test "x$watchdog" = "xyes"], [
@@ -344,7 +349,7 @@ Optional features:
   Install doc/..........: $enable_doc
   Install contrib/......: $enable_contrib
   Built-in keventd......: $with_keventd
-  Built-in sulogin......: $with_sulogin
+  Built-in sulogin......: $with_sulogin $sulogin
   Built-in watchdogd....: $with_watchdog $watchdog
   Built-in logrotate....: $enable_logrotate
   Skip fsck check.......: $enable_fastboot
diff --git a/src/sulogin.c b/src/sulogin.c
index 29ca4553..83197417 100644
--- a/src/sulogin.c
+++ b/src/sulogin.c
@@ -21,6 +21,8 @@
  * THE SOFTWARE.
  */
 
+#include "config.h"
+
 #include <crypt.h>
 #include <err.h>
 #include <paths.h>
@@ -32,6 +34,10 @@
 #include <unistd.h>
 #include <sys/ioctl.h>
 
+#ifndef SULOGIN_USER
+#define SULOGIN_USER "root"
+#endif
+
 /* getpwnam() cannot be used when statically linked */
 static int get_passwd(struct passwd *pw)
 {
@@ -44,13 +50,13 @@ static int get_passwd(struct passwd *pw)
 		return 1;
 
 	while ((tmp = fgets(buf, sizeof(buf), fp))) {
-		if (!strstr(buf, ":0:0:"))
-			continue;	/* not uid 0 */
-
 		ptr = strsep(&tmp, ":");
 		if (!ptr)
 			break;
+
 		pw->pw_name = strdup(ptr);
+		if (!pw->pw_name || strcmp(pw->pw_name, SULOGIN_USER))
+			continue;
 
 		ptr = strsep(&tmp, ":");
 		if (!ptr)