linux-hardening - [PATCH] s390/qeth: Split memcpy() of struct qeth_ipacmd_addr

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Date:   Mon, 26 Sep 2022 17:39:53 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Alexandra Winter <wintera@...ux.ibm.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Wenjia Zhang <wenjia@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        linux-s390@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] s390/qeth: Split memcpy() of struct qeth_ipacmd_addr_change flexible array

To work around a misbehavior of the compiler's ability to see into
composite flexible array structs (as detailed in the coming memcpy()
hardening series[1]), split the memcpy() of the header and the payload
so no false positive run-time overflow warning will be generated.

[1] https://lore.kernel.org/linux-hardening/20220901065914.1417829-2-keescook@chromium.org/

Cc: Alexandra Winter <wintera@...ux.ibm.com>
Cc: Wenjia Zhang <wenjia@...ux.ibm.com>
Cc: Heiko Carstens <hca@...ux.ibm.com>
Cc: Vasily Gorbik <gor@...ux.ibm.com>
Cc: Alexander Gordeev <agordeev@...ux.ibm.com>
Cc: Christian Borntraeger <borntraeger@...ux.ibm.com>
Cc: Sven Schnelle <svens@...ux.ibm.com>
Cc: linux-s390@...r.kernel.org
Cc: netdev@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 drivers/s390/net/qeth_l2_main.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/net/qeth_l2_main.c b/drivers/s390/net/qeth_l2_main.c
index 2d4436cbcb47..0ce635b7b472 100644
--- a/drivers/s390/net/qeth_l2_main.c
+++ b/drivers/s390/net/qeth_l2_main.c
@@ -1530,8 +1530,8 @@ static void qeth_addr_change_event(struct qeth_card *card,
 	else
 		INIT_DELAYED_WORK(&data->dwork, qeth_l2_dev2br_worker);
 	data->card = card;
-	memcpy(&data->ac_event, hostevs,
-			sizeof(struct qeth_ipacmd_addr_change) + extrasize);
+	data->ac_event = *hostevs;
+	memcpy(data->ac_event.entry, hostevs->entry, extrasize);
 	queue_delayed_work(card->event_wq, &data->dwork, 0);
 }
 
-- 
2.34.1