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

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Date:   Thu, 18 Nov 2021 12:21:26 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Doug Ledford <dledford@...hat.com>
Cc:     Kees Cook <keescook@...omium.org>, Jason Gunthorpe <jgg@...pe.ca>,
        Max Gurtovoy <maxg@...lanox.com>, linux-kernel@...r.kernel.org,
        linux-rdma@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] 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.

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 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