On Mon, Mar 02, 2015 at 01:27:05PM +0000, Patrick McHardy wrote: > On 02.03, Florian Westphal wrote: > > Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> wrote: > > > 2) TCPMSS. Relax the checking when used from nft_compat and make sure > > > that we skip !syn packets in case userspace provides a wrong > > > configuration. > > > diff --git a/net/netfilter/xt_TCPMSS.c b/net/netfilter/xt_TCPMSS.c > > > index e762de5..3b9761f 100644 > > > --- a/net/netfilter/xt_TCPMSS.c > > > +++ b/net/netfilter/xt_TCPMSS.c > > > @@ -97,6 +97,9 @@ tcpmss_mangle_packet(struct sk_buff *skb, > > > if (!skb_make_writable(skb, skb->len)) > > > return -1; > > > > > > + if (unlikely(!tcph->syn)) > > > + return 0; > > > + > > > len = skb->len - tcphoff; > > > > Applying this to my copy of nf-next would insert this test before > > tcph is set up. > > I actually don't think the test is necessary at all. Since we > don't check the protocol with nft, any packet with that bit set > will pass. It will most likely fail or corrupt the packet, but > why should we care? It won't crash and with nft its the > responsibility of userspace to take care of using the extension > correctly. According to what I can read from the code, it will corrupt the packet since we will get a MSS option in non-syn TCP packet. I thought we could crash, but looking at it again you seem to be right, I'm going to undo this change and send a v2. -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
