Patch "netfilter: xt_TCPMSS: add more sanity tests on tcph->doff" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

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 4.4-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-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 2638fd0f92d4397884fd991d8f4925cb3f081901 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@google.com>
Date: Mon, 3 Apr 2017 10:55:11 -0700
Subject: netfilter: xt_TCPMSS: add more sanity tests on tcph->doff

From: Eric Dumazet <edumazet@google.com>

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.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Denys Fedoryshchenko <nuclearcat@nuclearcat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/net/netfilter/xt_TCPMSS.c
+++ b/net/netfilter/xt_TCPMSS.c
@@ -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) {
@@ -156,6 +156,10 @@ 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 edumazet@google.com are

queue-4.4/fix-an-intermittent-pr_emerg-warning-about-lo-becoming-free.patch
queue-4.4/netfilter-xt_tcpmss-add-more-sanity-tests-on-tcph-doff.patch
queue-4.4/ipv6-release-dst-on-error-in-ip6_dst_lookup_tail.patch
queue-4.4/igmp-acquire-pmc-lock-for-ip_mc_clear_src.patch