[PATCH] dm snap : add sanity checks to snapshot_ctr

[Defang Bo <bodefang@126.com>]

Similar to commit<70de2cbda8a5>("dm thin: add sanity checks
to thin-pool and external snapshot creation"),there should be a check
for argc and argv to prevent Null pointer dereferencing when the dm_get_device
invoked twice on the same device path with differnt mode.

Signed-off-by: Defang Bo <bodefang@126.com>
---
 drivers/md/dm-snap.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 4668b2c..dccce8b 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -1258,6 +1258,13 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 
 	as.argc = argc;
 	as.argv = argv;
+
+	if (!strcmp(argv[0], argv[1])) {
+		ti->error = "Error setting metadata or data device";
+		r = -EINVAL;
+		goto bad;
+	}
+
 	dm_consume_args(&as, 4);
 	r = parse_snapshot_features(&as, s, ti);
 	if (r)
-- 
2.7.4