[Drbd-dev] [PATCH 10/17] drbd: Use struct_group() to zero algs

[Kees Cook]

In preparation for FORTIFY_SOURCE performing compile-time and run-time
field bounds checking for memset(), avoid intentionally writing across
neighboring fields.

Add a struct_group() for the algs so that memset() can correctly reason
about the size. "objdump -d" shows no changes to the executable
instructions.

Cc: Philipp Reisner <philipp.reisner at linbit.com>
Cc: Lars Ellenberg <lars.ellenberg at linbit.com>
Cc: Jens Axboe <axboe at kernel.dk>
Cc: drbd-dev at lists.linbit.com
Cc: linux-block at vger.kernel.org
Signed-off-by: Kees Cook <keescook at chromium.org>
---
 drivers/block/drbd/drbd_main.c     | 3 ++-
 drivers/block/drbd/drbd_protocol.h | 6 ++++--
 drivers/block/drbd/drbd_receiver.c | 3 ++-
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
index 07b3c6093e7d..6f450816c4fa 100644
--- a/drivers/block/drbd/drbd_main.c
+++ b/drivers/block/drbd/drbd_main.c
@@ -729,7 +729,8 @@ int drbd_send_sync_param(struct drbd_peer_device *peer_device)
 	cmd = apv >= 89 ? P_SYNC_PARAM89 : P_SYNC_PARAM;
 
 	/* initialize verify_alg and csums_alg */
-	memset(p->verify_alg, 0, 2 * SHARED_SECRET_MAX);
+	BUILD_BUG_ON(sizeof(p->algs) != 2 * SHARED_SECRET_MAX);
+	memset(&p->algs, 0, sizeof(p->algs));
 
 	if (get_ldev(peer_device->device)) {
 		dc = rcu_dereference(peer_device->device->ldev->disk_conf);
diff --git a/drivers/block/drbd/drbd_protocol.h b/drivers/block/drbd/drbd_protocol.h
index dea59c92ecc1..a882b65ab5d2 100644
--- a/drivers/block/drbd/drbd_protocol.h
+++ b/drivers/block/drbd/drbd_protocol.h
@@ -283,8 +283,10 @@ struct p_rs_param_89 {
 
 struct p_rs_param_95 {
 	u32 resync_rate;
-	char verify_alg[SHARED_SECRET_MAX];
-	char csums_alg[SHARED_SECRET_MAX];
+	struct_group(algs,
+		char verify_alg[SHARED_SECRET_MAX];
+		char csums_alg[SHARED_SECRET_MAX];
+	);
 	u32 c_plan_ahead;
 	u32 c_delay_target;
 	u32 c_fill_target;
diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index 1f740e42e457..6df2539e215b 100644
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -3921,7 +3921,8 @@ static int receive_SyncParam(struct drbd_connection *connection, struct packet_i
 
 	/* initialize verify_alg and csums_alg */
 	p = pi->data;
-	memset(p->verify_alg, 0, 2 * SHARED_SECRET_MAX);
+	BUILD_BUG_ON(sizeof(p->algs) != 2 * SHARED_SECRET_MAX);
+	memset(&p->algs, 0, sizeof(p->algs));
 
 	err = drbd_recv_all(peer_device->connection, p, header_size);
 	if (err)
-- 
2.30.2