Commit f4549a69 authored Apr 03, 2017 by Eric Dumazet Committed by Greg Kroah-Hartman Jul 05, 2017

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



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>

parent 51ef22af

net/netfilter/xt_TCPMSS.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -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..
		*/