linux-hardening - [PATCH] net: 802: Use memset_startat() to clear struct fields

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Date:   Thu, 18 Nov 2021 12:30:45 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Jes Sorensen <jes@...ined-monkey.org>
Cc:     Kees Cook <keescook@...omium.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, linux-kernel@...r.kernel.org,
        linux-hippi@...site.dk, netdev@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: [PATCH] net: 802: Use memset_startat() to clear struct fields

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>
---
 net/802/hippi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/802/hippi.c b/net/802/hippi.c
index 887e73d520e4..1997b7dd265e 100644
--- a/net/802/hippi.c
+++ b/net/802/hippi.c
@@ -65,7 +65,7 @@ static int hippi_header(struct sk_buff *skb, struct net_device *dev,
 	hip->le.src_addr_type	= 2;	/* 12 bit SC address */
 
 	memcpy(hip->le.src_switch_addr, dev->dev_addr + 3, 3);
-	memset(&hip->le.reserved, 0, 16);
+	memset_startat(&hip->le, 0, reserved);
 
 	hip->snap.dsap		= HIPPI_EXTENDED_SAP;
 	hip->snap.ssap		= HIPPI_EXTENDED_SAP;
-- 
2.30.2