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

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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>
This commit is contained in:
Eric Dumazet 2017-04-03 10:55:11 -07:00 committed by Pablo Neira Ayuso
parent 0b9aefea86
commit 2638fd0f92
1 changed files with 5 additions and 1 deletions
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6
net/netfilter/xt_TCPMSS.c
View File

@ -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..
*/