[PATCH] mtd: ubi: avoid NULL pointer dereference in ubi_get_device

[Philipp Zabel]

If the ubidetach command is given a number that passes the range check
in ubi_detach_mtd_dev, but at which index the ubi_devices array contains
a NULL pointer, ubi_get_device tries to dereference this NULL pointer
to increment the ubi device reference count.

Signed-off-by: Philipp Zabel <p.zabel at pengutronix.de>
---
 drivers/mtd/ubi/build.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/mtd/ubi/build.c b/drivers/mtd/ubi/build.c
index da21f69..b908fcd 100644
--- a/drivers/mtd/ubi/build.c
+++ b/drivers/mtd/ubi/build.c
@@ -104,6 +104,8 @@ struct ubi_device *ubi_get_device(int ubi_num)
 	struct ubi_device *ubi;
 
 	ubi = ubi_devices[ubi_num];
+	if (!ubi)
+		return NULL;
 
 	ubi->ref_count++;
 
-- 
1.9.0