drbd: Use struct_group() to zero algs

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.

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20211118203712.1288866-1-keescook@chromium.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
index 07b3c60..6f45081 100644 (file)
--- 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 dea59c9..a882b65 100644 (file)
--- 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 1f740e4..6df2539 100644 (file)
--- 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)