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

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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>
[wt: adjust context]

Signed-off-by: Willy Tarreau <w@1wt.eu>
This commit is contained in:
Eric Dumazet
2017-04-03 10:55:11 -07:00
committed by Willy Tarreau
parent 946272f8a5
commit 72d7b83afb
1 changed files with 5 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files
net/netfilter/xt_TCPMSS.c
+5 -1
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@@ -68,7 +68,7 @@ tcpmss_mangle_packet(struct sk_buff *skb,
tcph = (struct tcphdr *)(skb_network_header(skb) + tcphoff);
/* Header cannot be larger than the packet */
if (tcplen < tcph->doff*4)
if (tcplen < tcph->doff*4 || tcph->doff*4 < sizeof(struct tcphdr))
return -1;
if (info->mss == XT_TCPMSS_CLAMP_PMTU) {
@@ -117,6 +117,10 @@ tcpmss_mangle_packet(struct sk_buff *skb,
if (tcplen > tcph->doff*4)
return 0;
/* tcph->doff has 4 bits, do not wrap it to 0 */
if (tcph->doff >= 15)
return 0;
/*
* MSS Option not found ?! add it..
*/