[PATCH] um: ubd: fix command line handling of ubd

[Hajime Tazaki]

This commit fixes a regression to handle command line parameters of ubd.
With a simple line "./linux ubd0="./disk-ext4.img", it fails at
ubd_setup_common().  The commit adds additional checks to the variables
in order to properly parse the paremeters which previously worked.

Fixes: ef3ba87cb7c9 ("um: ubd: Set device serial attribute from
cmdline")
Cc: Christopher Obbard <chris.obbard at collabora.com>
Signed-off-by: Hajime Tazaki <thehajime at gmail.com>
---
 arch/um/drivers/ubd_kern.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/um/drivers/ubd_kern.c b/arch/um/drivers/ubd_kern.c
index 13b1fe694b90..bd16b17ba4d6 100644
--- a/arch/um/drivers/ubd_kern.c
+++ b/arch/um/drivers/ubd_kern.c
@@ -375,11 +375,11 @@ static int ubd_setup_common(char *str, int *index_out, char **error_out)
 		file = NULL;
 
 	backing_file = strsep(&str, ",:");
-	if (*backing_file == '\0')
+	if (backing_file && *backing_file == '\0')
 		backing_file = NULL;
 
 	serial = strsep(&str, ",:");
-	if (*serial == '\0')
+	if (serial && *serial == '\0')
 		serial = NULL;
 
 	if (backing_file && ubd_dev->no_cow) {
-- 
2.17.2