[PATCH 4.9 43/56] Disable kgdboc failed by echo space to /sys/module/kgdboc/parameters/kgdboc

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Wentao Wang <witallwang@xxxxxxxxx>

commit 3ec8002951ea173e24b466df1ea98c56b7920e63 upstream.

Echo "" to /sys/module/kgdboc/parameters/kgdboc will fail with "No such
deviceâ error.

This is caused by function "configure_kgdboc" who init err to ENODEV
when the config is empty (legal input) the code go out with ENODEV
returned.

Fixes: 2dd453168643 ("kgdboc: Fix restrict error")
Signed-off-by: Wentao Wang <witallwang@xxxxxxxxx>
Cc: stable <stable@xxxxxxxxxxxxxxx>
Acked-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/tty/serial/kgdboc.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/drivers/tty/serial/kgdboc.c
+++ b/drivers/tty/serial/kgdboc.c
@@ -148,8 +148,10 @@ static int configure_kgdboc(void)
 	char *cptr = config;
 	struct console *cons;
 
-	if (!strlen(config) || isspace(config[0]))
+	if (!strlen(config) || isspace(config[0])) {
+		err = 0;
 		goto noconfig;
+	}
 
 	kgdboc_io_ops.is_console = 0;
 	kgdb_tty_driver = NULL;