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From: Pablo Neira Ayuso <pablo@netfilter.org>
To: netfilter-devel@vger.kernel.org
Cc: davem@davemloft.net, netdev@vger.kernel.org
Subject: [PATCH 1/9] netfilter: xt_TCPMSS: add more sanity tests on tcph->doff
Date: Fri, 14 Apr 2017 02:26:43 +0200
Message-ID: <1492129611-29336-2-git-send-email-pablo@netfilter.org> (raw)
In-Reply-To: <1492129611-29336-1-git-send-email-pablo@netfilter.org>

From: Eric Dumazet <edumazet@google.com>

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

diff --git a/net/netfilter/xt_TCPMSS.c b/net/netfilter/xt_TCPMSS.c
index 27241a767f17..c64aca611ac5 100644
--- 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) {
@@ -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..
 	 */
-- 
2.1.4


  reply index

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-04-14  0:26 [PATCH 0/9] Netfilter fixes for net Pablo Neira Ayuso
2017-04-14  0:26 ` Pablo Neira Ayuso [this message]
2017-04-14  0:26 ` [PATCH 2/9] netfilter: ctnetlink: using bit to represent the ct event Pablo Neira Ayuso
2017-04-14  0:26 ` [PATCH 3/9] netfilter: helper: Add the rcu lock when call __nf_conntrack_helper_find Pablo Neira Ayuso
2017-04-14  0:26 ` [PATCH 4/9] netfilter: ctnetlink: make it safer when checking the ct helper name Pablo Neira Ayuso
2017-04-14  0:26 ` [PATCH 5/9] netfilter: make it safer during the inet6_dev->addr_list traversal Pablo Neira Ayuso
2017-04-14  0:26 ` [PATCH 6/9] netfilter: ctnetlink: skip dumping expect when nfct_help(ct) is NULL Pablo Neira Ayuso
2017-04-14  0:26 ` [PATCH 7/9] netfilter: nf_ct_expect: use proper RCU list traversal/update APIs Pablo Neira Ayuso
2017-04-14  0:26 ` [PATCH 8/9] netfilter: nft_hash: do not dump the auto generated seed Pablo Neira Ayuso
2017-04-14  0:26 ` [PATCH 9/9] netfilter: ipt_CLUSTERIP: Fix wrong conntrack netns refcnt usage Pablo Neira Ayuso
2017-04-14 14:59 ` [PATCH 0/9] Netfilter fixes for net David Miller

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