linux-kernel - [PATCH 3.2 62/79] netfilter: xt_TCPOPTSTRIP: don't use tcp

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Date:   Sun, 11 Feb 2018 04:20:06 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Phil Oester" <kernel@...uxace.com>,
        "Pablo Neira Ayuso" <pablo@...filter.org>,
        "Florian Westphal" <fw@...len.de>
Subject: [PATCH 3.2 62/79] netfilter: xt_TCPOPTSTRIP: don't use tcp_hdr()

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

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

From: Pablo Neira Ayuso <pablo@...filter.org>

commit ed82c437320c48a4032492f4a55a7e2c934158b6 upstream.

In (bc6bcb5 netfilter: xt_TCPOPTSTRIP: fix possible mangling beyond
packet boundary), the use of tcp_hdr was introduced. However, we
cannot assume that skb->transport_header is set for non-local packets.

Cc: Florian Westphal <fw@...len.de>
Reported-by: Phil Oester <kernel@...uxace.com>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/netfilter/xt_TCPOPTSTRIP.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/net/netfilter/xt_TCPOPTSTRIP.c
+++ b/net/netfilter/xt_TCPOPTSTRIP.c
@@ -48,11 +48,13 @@ tcpoptstrip_mangle_packet(struct sk_buff
 		return NF_DROP;
 
 	len = skb->len - tcphoff;
-	if (len < (int)sizeof(struct tcphdr) ||
-	    tcp_hdr(skb)->doff * 4 > len)
+	if (len < (int)sizeof(struct tcphdr))
 		return NF_DROP;
 
 	tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
+	if (tcph->doff * 4 > len)
+		return NF_DROP;
+
 	opt  = (u_int8_t *)tcph;
 
 	/*