[ 3.5.y.z extended stable ] Patch "netfilter: xt_TCPOPTSTRIP: fix possible mangling beyond" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    netfilter: xt_TCPOPTSTRIP: fix possible mangling beyond

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 69e92e09a54da760c52b848d99638936dc270d9e Mon Sep 17 00:00:00 2001
From: Pablo Neira Ayuso <pablo at netfilter.org>
Date: Tue, 7 May 2013 03:22:18 +0200
Subject: [PATCH] netfilter: xt_TCPOPTSTRIP: fix possible mangling beyond
 packet boundary

commit bc6bcb59dd7c184d229f9e86d08aa56059938a4c upstream.

This target assumes that tcph->doff is well-formed, that may be well
not the case. Add extra sanity checkings to avoid possible crash due
to read/write out of the real packet boundary. After this patch, the
default action on malformed TCP packets is to drop them. Moreover,
fragments are skipped.

Reported-by: Rafal Kupka <rkupka at telemetry.com>
Signed-off-by: Pablo Neira Ayuso <pablo at netfilter.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/netfilter/xt_TCPOPTSTRIP.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/net/netfilter/xt_TCPOPTSTRIP.c b/net/netfilter/xt_TCPOPTSTRIP.c
index 25fd1c4..1eb1a44 100644
--- a/net/netfilter/xt_TCPOPTSTRIP.c
+++ b/net/netfilter/xt_TCPOPTSTRIP.c
@@ -30,17 +30,28 @@ static inline unsigned int optlen(const u_int8_t *opt, unsigned int offset)

 static unsigned int
 tcpoptstrip_mangle_packet(struct sk_buff *skb,
-			  const struct xt_tcpoptstrip_target_info *info,
+			  const struct xt_action_param *par,
 			  unsigned int tcphoff, unsigned int minlen)
 {
+	const struct xt_tcpoptstrip_target_info *info = par->targinfo;
 	unsigned int optl, i, j;
 	struct tcphdr *tcph;
 	u_int16_t n, o;
 	u_int8_t *opt;
+	int len;
+
+	/* This is a fragment, no TCP header is available */
+	if (par->fragoff != 0)
+		return XT_CONTINUE;

 	if (!skb_make_writable(skb, skb->len))
 		return NF_DROP;

+	len = skb->len - tcphoff;
+	if (len < (int)sizeof(struct tcphdr) ||
+	    tcp_hdr(skb)->doff * 4 > len)
+		return NF_DROP;
+
 	tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
 	opt  = (u_int8_t *)tcph;

@@ -76,7 +87,7 @@ tcpoptstrip_mangle_packet(struct sk_buff *skb,
 static unsigned int
 tcpoptstrip_tg4(struct sk_buff *skb, const struct xt_action_param *par)
 {
-	return tcpoptstrip_mangle_packet(skb, par->targinfo, ip_hdrlen(skb),
+	return tcpoptstrip_mangle_packet(skb, par, ip_hdrlen(skb),
 	       sizeof(struct iphdr) + sizeof(struct tcphdr));
 }

@@ -94,7 +105,7 @@ tcpoptstrip_tg6(struct sk_buff *skb, const struct xt_action_param *par)
 	if (tcphoff < 0)
 		return NF_DROP;

-	return tcpoptstrip_mangle_packet(skb, par->targinfo, tcphoff,
+	return tcpoptstrip_mangle_packet(skb, par, tcphoff,
 	       sizeof(*ipv6h) + sizeof(struct tcphdr));
 }
 #endif
--
1.8.1.2