From 5a9fb75c653eb65d249f5158666029a0bb0f8137 Mon Sep 17 00:00:00 2001
From: phoebos <ben@bvnf.space>
Date: Mon, 9 May 2022 17:01:41 +0100
Subject: [PATCH] su: support numeric UIDs with a -n flag

---
 loginutils/su.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/loginutils/su.c b/loginutils/su.c
index 6efe1981a..51c6d9885 100644
--- a/loginutils/su.c
+++ b/loginutils/su.c
@@ -35,10 +35,11 @@
 //kbuild:lib-$(CONFIG_SU) += su.o
 
 //usage:#define su_trivial_usage
-//usage:       "[-lmp] [-s SH] [-] [USER [FILE ARGS | -c 'CMD' [ARG0 ARGS]]]"
+//usage:       "[-lnmp] [-s SH] [-] [USER [FILE ARGS | -c 'CMD' [ARG0 ARGS]]]"
 //usage:#define su_full_usage "\n\n"
 //usage:       "Run shell under USER (by default, root)\n"
 //usage:     "\n	-,-l	Clear environment, go to home dir, run shell as login shell"
+//usage:     "\n	-n  	Interpret USER as numeric ID"
 //usage:     "\n	-p,-m	Do not set new $HOME, $SHELL, $USER, $LOGNAME"
 //usage:     "\n	-c CMD	Command to pass to 'sh -c'"
 //usage:     "\n	-s SH	Shell to use instead of user's default"
@@ -69,6 +70,7 @@ static int restricted_shell(const char *shell)
 
 #define SU_OPT_mp (3)
 #define SU_OPT_l  (4)
+#define SU_OPT_n  (32)
 
 int su_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int su_main(int argc UNUSED_PARAM, char **argv)
@@ -91,7 +93,7 @@ int su_main(int argc UNUSED_PARAM, char **argv)
 	 * ARGS starting with dash will be treated as su options,
 	 * not passed to shell. (Tested on util-linux 2.28).
 	 */
-	flags = getopt32(argv, "mplc:s:", &opt_command, &opt_shell);
+	flags = getopt32(argv, "mplc:s:n", &opt_command, &opt_shell);
 	argv += optind;
 
 	if (argv[0] && LONE_DASH(argv[0])) {
@@ -103,6 +105,8 @@ int su_main(int argc UNUSED_PARAM, char **argv)
 	if (argv[0]) {
 		opt_username = argv[0];
 		argv++;
+	} else if (flags & SU_OPT_n) {
+		opt_username = "0";
 	}
 
 	tty = xmalloc_ttyname(STDIN_FILENO);
@@ -126,7 +130,14 @@ int su_main(int argc UNUSED_PARAM, char **argv)
 		openlog(applet_name, 0, LOG_AUTH);
 	}
 
-	pw = xgetpwnam(opt_username);
+	if (flags & SU_OPT_n) {
+		unsigned long uid = bb_strtoul(opt_username, NULL, 10);
+		if (uid == ULLONG_MAX)
+			bb_error_msg_and_die("invalid uid %s", opt_username);
+		pw = xgetpwuid((uid_t)uid);
+	} else {
+		pw = xgetpwnam(opt_username);
+	}
 
 	r = 1;
 	if (cur_uid != 0)
-- 
2.36.1