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

Use memset_startat() so memset() doesn't get confused about writing
beyond the destination member that is intended to be the starting point
of zeroing through the end of the struct. Additionally, since everything
appears to perform a roundup (including allocation), just change the
size of the struct itself and add a build-time check to validate the
expected size.

Cc: Potnuri Bharat Teja <bha...@chelsio.com>
Cc: Doug Ledford <dledf...@redhat.com>
Cc: Jason Gunthorpe <j...@ziepe.ca>
Cc: Raju Rangoju <ra...@chelsio.com>
Cc: "David S. Miller" <da...@davemloft.net>
Cc: Jakub Kicinski <k...@kernel.org>
Cc: linux-r...@vger.kernel.org
Cc: net...@vger.kernel.org
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
 drivers/infiniband/hw/cxgb4/cm.c            | 5 +++--
 drivers/net/ethernet/chelsio/cxgb4/t4_msg.h | 2 +-
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/infiniband/hw/cxgb4/cm.c b/drivers/infiniband/hw/cxgb4/cm.c
index 291471d12197..6519ea8ebf23 100644
--- a/drivers/infiniband/hw/cxgb4/cm.c
+++ b/drivers/infiniband/hw/cxgb4/cm.c
@@ -2471,7 +2471,8 @@ static int accept_cr(struct c4iw_ep *ep, struct sk_buff 
*skb,
        skb_get(skb);
        rpl = cplhdr(skb);
        if (!is_t4(adapter_type)) {
-               skb_trim(skb, roundup(sizeof(*rpl5), 16));
+               BUILD_BUG_ON(sizeof(*rpl5) != roundup(sizeof(*rpl5), 16));
+               skb_trim(skb, sizeof(*rpl5));
                rpl5 = (void *)rpl;
                INIT_TP_WR(rpl5, ep->hwtid);
        } else {
@@ -2487,7 +2488,7 @@ static int accept_cr(struct c4iw_ep *ep, struct sk_buff 
*skb,
                opt2 |= CONG_CNTRL_V(CONG_ALG_TAHOE);
                opt2 |= T5_ISS_F;
                rpl5 = (void *)rpl;
-               memset(&rpl5->iss, 0, roundup(sizeof(*rpl5)-sizeof(*rpl), 16));
+               memset_after(rpl5, 0, iss);
                if (peer2peer)
                        isn += 4;
                rpl5->iss = cpu_to_be32(isn);
diff --git a/drivers/net/ethernet/chelsio/cxgb4/t4_msg.h 
b/drivers/net/ethernet/chelsio/cxgb4/t4_msg.h
index fed5f93bf620..26433a62d7f0 100644
--- a/drivers/net/ethernet/chelsio/cxgb4/t4_msg.h
+++ b/drivers/net/ethernet/chelsio/cxgb4/t4_msg.h
@@ -497,7 +497,7 @@ struct cpl_t5_pass_accept_rpl {
        __be32 opt2;
        __be64 opt0;
        __be32 iss;
-       __be32 rsvd;
+       __be32 rsvd[3];
 };
 
 struct cpl_act_open_req {
-- 
2.30.2

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