dm mpath: fix potential NULL pointer in feature arg processing

commit 286f367d upstream.

Avoid dereferencing a NULL pointer if the number of feature arguments
supplied is fewer than indicated.
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/md/dm-mpath.c

@@ -778,6 +778,11 @@ static int parse_features(struct arg_set *as, struct multipath *m)
 	if (!argc)
 		return 0;
 
+	if (argc > as->argc) {
+		ti->error = "not enough arguments for features";
+		return -EINVAL;
+	}
+
 	do {
 		param_name = shift(as);
 		argc--;