Re: [PATCH 48/64] drbd: Use struct_group() to zero algs

Bart Van Assche
2021-07-28T21:46:02Z

On 7/27/21 1:58 PM, Kees Cook wrote:
> 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>
> ---
> 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 55234a558e98..b824679cfcb2 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));

Using struct_group() introduces complexity. Has it been considered not
to modify struct p_rs_param_95 and instead to use two memset() calls
instead of one (one memset() call per member)?

Thanks,

Bart.