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

[Bart Van Assche]

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 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 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.