1 files changed, 21 insertions, 2 deletions
diff --git a/libbb/change_identity.c b/libbb/change_identity.c
index 619db09a8..d48d86326 100644
--- a/libbb/change_identity.c
+++ b/libbb/change_identity.c
@@ -33,9 +33,28 @@
 /* Become the user and group(s) specified by PW.  */
 void FAST_FUNC change_identity(const struct passwd *pw)
 {
-	if (initgroups(pw->pw_name, pw->pw_gid) == -1)
-		bb_perror_msg_and_die("can't set groups");
+	int res;
+
+	res = initgroups(pw->pw_name, pw->pw_gid);
 	endgrent(); /* helps to close a fd used internally by libc */
+
+	if (res != 0) {
+		/*
+		 * If initgroups() fails because a system call is unimplemented
+		 * then we are running on a Linux kernel compiled without multiuser
+		 * support (CONFIG_MULTIUSER is not defined).
+		 *
+		 * If we are running without multiuser support *and* the target uid
+		 * already matches the current uid then we can skip the change of
+		 * identity.
+		 */
+		if (errno == ENOSYS && pw->pw_uid == getuid()) {
+			return;
+		}
+
+		bb_perror_msg_and_die("can't set groups");
+	}
+
 	xsetgid(pw->pw_gid);
 	xsetuid(pw->pw_uid);
 }