linux-hardening - [PATCH 14/17] IB/mthca: Use memset_startat() for clearing mpt

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Date:   Mon, 13 Dec 2021 14:33:28 -0800
From:   Kees Cook <keescook@...omium.org>
To:     linux-hardening@...r.kernel.org
Cc:     Kees Cook <keescook@...omium.org>,
        Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Max Gurtovoy <maxg@...lanox.com>, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 14/17] IB/mthca: Use memset_startat() for clearing mpt_entry

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 <dledford@...hat.com>
Cc: Jason Gunthorpe <jgg@...pe.ca>
Cc: Max Gurtovoy <maxg@...lanox.com>
Cc: linux-rdma@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.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 a59100c496b4..192f83fd7c8a 100644
--- a/drivers/infiniband/hw/mthca/mthca_mr.c
+++ b/drivers/infiniband/hw/mthca/mthca_mr.c
@@ -467,8 +467,7 @@ 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