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.

Cc: Doug Ledford <dledf...@redhat.com>
Cc: Jason Gunthorpe <j...@ziepe.ca>
Cc: Max Gurtovoy <m...@mellanox.com>
Cc: linux-r...@vger.kernel.org
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
 drivers/infiniband/hw/mthca/mthca_mr.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/infiniband/hw/mthca/mthca_mr.c 
b/drivers/infiniband/hw/mthca/mthca_mr.c
index ce0e0867e488..1208e92ca3d3 100644
--- a/drivers/infiniband/hw/mthca/mthca_mr.c
+++ b/drivers/infiniband/hw/mthca/mthca_mr.c
@@ -469,8 +469,7 @@ int mthca_mr_alloc(struct mthca_dev *dev, u32 pd, int 
buffer_size_shift,
        mpt_entry->start     = cpu_to_be64(iova);
        mpt_entry->length    = cpu_to_be64(total_size);
 
-       memset(&mpt_entry->lkey, 0,
-              sizeof *mpt_entry - offsetof(struct mthca_mpt_entry, lkey));
+       memset_startat(mpt_entry, 0, lkey);
 
        if (mr->mtt)
                mpt_entry->mtt_seg =
-- 
2.30.2

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