linux-kernel - [PATCH 3.16 080/202] l2tp: copy 4 more bytes to linear part if necessary

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Message-ID: <lsq.1556377989.545615296@decadent.org.uk>
Date:   Sat, 27 Apr 2019 16:13:09 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Jacob Wen" <jian.w.wen@...cle.com>,
        "Guillaume Nault" <gnault@...hat.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 3.16 080/202] l2tp: copy 4 more bytes to linear part if
 necessary

3.16.66-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Jacob Wen <jian.w.wen@...cle.com>

commit 91c524708de6207f59dd3512518d8a1c7b434ee3 upstream.

The size of L2TPv2 header with all optional fields is 14 bytes.
l2tp_udp_recv_core only moves 10 bytes to the linear part of a
skb. This may lead to l2tp_recv_common read data outside of a skb.

This patch make sure that there is at least 14 bytes in the linear
part of a skb to meet the maximum need of l2tp_udp_recv_core and
l2tp_recv_common. The minimum size of both PPP HDLC-like frame and
Ethernet frame is larger than 14 bytes, so we are safe to do so.

Also remove L2TP_HDR_SIZE_NOSEQ, it is unused now.

Fixes: fd558d186df2 ("l2tp: Split pppol2tp patch into separate l2tp and ppp parts")
Suggested-by: Guillaume Nault <gnault@...hat.com>
Signed-off-by: Jacob Wen <jian.w.wen@...cle.com>
Acked-by: Guillaume Nault <gnault@...hat.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/l2tp/l2tp_core.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -82,8 +82,7 @@
 #define L2TP_SLFLAG_S	   0x40000000
 #define L2TP_SL_SEQ_MASK   0x00ffffff
 
-#define L2TP_HDR_SIZE_SEQ		10
-#define L2TP_HDR_SIZE_NOSEQ		6
+#define L2TP_HDR_SIZE_MAX		14
 
 /* Default trace flags */
 #define L2TP_DEFAULT_DEBUG_FLAGS	0
@@ -897,7 +896,7 @@ static int l2tp_udp_recv_core(struct l2t
 	__skb_pull(skb, sizeof(struct udphdr));
 
 	/* Short packet? */
-	if (!pskb_may_pull(skb, L2TP_HDR_SIZE_SEQ)) {
+	if (!pskb_may_pull(skb, L2TP_HDR_SIZE_MAX)) {
 		l2tp_info(tunnel, L2TP_MSG_DATA,
 			  "%s: recv short packet (len=%d)\n",
 			  tunnel->name, skb->len);