On Sun, 2017-04-02 at 10:14 -0700, Eric Dumazet wrote:
> Could that be that netfilter does not abort earlier if TCP header is
> completely wrong ?
>
Yes, I wonder if this patch would be better, unless we replicate the
th->doff sanity check in all netfilter modules dissecting TCP frames.
diff --git a/net/netfilter/xt_tcpudp.c b/net/netfilter/xt_tcpudp.c
index ade024c90f4f129a7c384e9e1cbfdb8ffe73065f..8cb4eadd5ba1c20e74bc27ee52a0bc36a5b26725 100644
--- a/net/netfilter/xt_tcpudp.c
+++ b/net/netfilter/xt_tcpudp.c
@@ -103,11 +103,11 @@ static bool tcp_mt(const struct sk_buff *skb, struct xt_action_param *par)
if (!NF_INVF(tcpinfo, XT_TCP_INV_FLAGS,
(((unsigned char *)th)[13] & tcpinfo->flg_mask) == tcpinfo->flg_cmp))
return false;
+ if (th->doff * 4 < sizeof(_tcph)) {
+ par->hotdrop = true;
+ return false;
+ }
if (tcpinfo->option) {
- if (th->doff * 4 < sizeof(_tcph)) {
- par->hotdrop = true;
- return false;
- }
if (!tcp_find_option(tcpinfo->option, skb, par->thoff,
th->doff*4 - sizeof(_tcph),
tcpinfo->invflags & XT_TCP_INV_OPTION,
--
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