dm verity: set DM_TARGET_IMMUTABLE feature flag

commit 4caae58406 upstream.

The device-mapper framework provides a mechanism to mark targets as
immutable (and hence fail table reloads that try to change the target
type). Add the DM_TARGET_IMMUTABLE flag to the dm-verity target's
feature flags to prevent switching the verity target with a different
target type.

Fixes: a4ffc15219 ("dm: add verity target")
Cc: stable@vger.kernel.org
Signed-off-by: Sarthak Kukreti <sarthakkukreti@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Tao Wu <tallwu@tencent.com>
Reviewed-by: Alex Shi <alexsshi@tencent.com>

drivers/md/dm-verity-target.c

@@ -1217,6 +1217,7 @@ bad:
 
 static struct target_type verity_target = {
 	.name		= "verity",
+	.features	= DM_TARGET_IMMUTABLE,
 	.version	= {1, 5, 0},
 	.module		= THIS_MODULE,
 	.ctr		= verity_ctr,