netdev - [PATCH net-next ] mpls: In mpls_egress verify the packet length.

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Message-ID: <87a8zhztpo.fsf@x220.int.ebiederm.org>
Date:	Thu, 12 Mar 2015 18:22:59 -0500
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	David Miller <davem@...emloft.net>
Cc:	rshearma@...cade.com, netdev@...r.kernel.org
Subject: [PATCH net-next ] mpls: In mpls_egress verify the packet length.


Reobert Shearman noticed that mpls_egress is failing to verify that
the bytes to be examined are in fact present in the packet before
mpls_egress reads those bytes.

As suggested by David Miller reduce this to a single pskb_may_pull
call so that we don't do unnecessary work in the fast path.

Reported-by: Robert Shearman <rshearma@...cade.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 net/mpls/af_mpls.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/net/mpls/af_mpls.c b/net/mpls/af_mpls.c
index 0ad8f7141be2..db8a2ea6d4de 100644
--- a/net/mpls/af_mpls.c
+++ b/net/mpls/af_mpls.c
@@ -92,9 +92,24 @@ static bool mpls_egress(struct mpls_route *rt, struct sk_buff *skb,
 	 * The strange cases if we choose to support them will require
 	 * manual configuration.
 	 */
-	struct iphdr *hdr4 = ip_hdr(skb);
+	struct iphdr *hdr4;
 	bool success = true;
 
+	/* The IPv4 code below accesses through the IPv4 header
+	 * checksum, which is 12 bytes into the packet.
+	 * The IPv6 code below accesses through the IPv6 hop limit
+	 * which is 8 bytes into the packet.
+	 *
+	 * For all supported cases there should always be at least 12
+	 * bytes of packet data present.  The IPv4 header is 20 bytes
+	 * without options and the IPv6 header is always 40 bytes
+	 * long.
+	 */
+	if (!pskb_may_pull(skb, 12))
+		return false;
+
+	/* Use ip_hdr to find the ip protocol version */
+	hdr4 = ip_hdr(skb);
 	if (hdr4->version == 4) {
 		skb->protocol = htons(ETH_P_IP);
 		csum_replace2(&hdr4->check,
-- 
2.2.1

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