[PATCH v2] sulogin: allow system maintenance login if root password is empty

[Jonathan Liu]

The current password checking is unable to distinguish between the user
entering an empty password or pressing Control-D. As a result, an empty
password always results in normal startup.

We modify bb_ask to return NULL if Control-D is pressed without entering
a password. The sulogin applet is then modified to only proceed to
normal startup if bb_ask returns NULL. This covers EOF with no password,
interrupt by timeout and ^C.

Signed-off-by: Jonathan Liu <net147 at gmail.com>
---
 libbb/bb_askpass.c   | 4 ++--
 loginutils/sulogin.c | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/libbb/bb_askpass.c b/libbb/bb_askpass.c
index fe2b506..e875bdd 100644
--- a/libbb/bb_askpass.c
+++ b/libbb/bb_askpass.c
@@ -65,8 +65,8 @@ char* FAST_FUNC bb_ask(const int fd, int timeout, const char *prompt)
 	i = 0;
 	while (1) {
 		int r = read(fd, &ret[i], 1);
-		if (r < 0) {
-			/* read is interrupted by timeout or ^C */
+		if ((i == 0 && r == 0) || r < 0) {
+			/* EOF with no password, read is interrupted by timeout or ^C */
 			ret = NULL;
 			break;
 		}
diff --git a/loginutils/sulogin.c b/loginutils/sulogin.c
index bd2b09e..6df0437 100644
--- a/loginutils/sulogin.c
+++ b/loginutils/sulogin.c
@@ -84,7 +84,7 @@ int sulogin_main(int argc UNUSED_PARAM, char **argv)
 				"Give root password for system maintenance\n"
 				"(or type Control-D for normal startup):");
 
-		if (!cp || !*cp) {
+		if (!cp) {
 			bb_info_msg("Normal startup");
 			return 0;
 		}
-- 
1.8.2.3