Patch "netfilter: xt_TCPMSS: add more sanity tests on tcph->doff" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

    netfilter: xt_TCPMSS: add more sanity tests on tcph->doff

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
netfilter-xt_tcpmss-add-more-sanity-tests-on-tcph-doff.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Eric Dumazet <[email protected]>
Date: Mon, 3 Apr 2017 10:55:11 -0700
Subject: netfilter: xt_TCPMSS: add more sanity tests on tcph->doff

From: Eric Dumazet <[email protected]>

commit 2638fd0f92d4397884fd991d8f4925cb3f081901 upstream.

Denys provided an awesome KASAN report pointing to an use after free in xt_TCPMSS

I have provided three patches to fix this issue, either in xt_TCPMSS or in xt_tcpudp.c. It seems xt_TCPMSS patch has the smallest possible impact.

---
 net/netfilter/xt_TCPMSS.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

@@ -104,7 +104,7 @@ tcpmss_mangle_packet(struct sk_buff *skb
 	tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
 	tcp_hdrlen = tcph->doff * 4;
 
-	if (len < tcp_hdrlen)
+	if (len < tcp_hdrlen || tcp_hdrlen < sizeof(struct tcphdr))
 		return -1;
 
 	if (info->mss == XT_TCPMSS_CLAMP_PMTU) {

@@ -152,6 +152,10 @@ tcpmss_mangle_packet(struct sk_buff *skb
 	if (len > tcp_hdrlen)
 		return 0;
 
+	/* tcph->doff has 4 bits, do not wrap it to 0 */
+	if (tcp_hdrlen >= 15 * 4)
+		return 0;
+
 	/*
 	 * MSS Option not found ?! add it..
 	 */

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/fix-an-intermittent-pr_emerg-warning-about-lo-becoming-free.patch queue-4.9/netfilter-xt_tcpmss-add-more-sanity-tests-on-tcph-doff.patch queue-4.9/ipv6-release-dst-on-error-in-ip6_dst_lookup_tail.patch queue-4.9/igmp-acquire-pmc-lock-for-ip_mc_clear_src.patch