On Thu, Jul 29, 2021 at 07:57:47PM -0700, Bart Van Assche wrote:
> On 7/29/21 7:31 PM, Kees Cook wrote:
> > On Wed, Jul 28, 2021 at 02:45:55PM -0700, Bart Van Assche wrote:
> >> 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@xxxxxxxxxxxx>
> >>> ---
> >>> 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)?
> >
> > I went this direction because using two memset()s (or memcpy()s in other
> > patches) changes the machine code. It's not much of a change, but it
> > seems easier to justify "no binary changes" via the use of struct_group().
> >
> > If splitting the memset() is preferred, I can totally do that instead.
> > :)
>
> I don't have a strong opinion about this. Lars, do you want to comment
> on this patch?
Fine either way. "no binary changes" sounds good ;-)
Thanks,
Lars
