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Date: Mon, 19 May 2014 22:49:32 +0200 From: Bart De Schuymer <bdschuym@...dora.be> To: Florian Westphal <fw@...len.de>, David Newall <davidn@...idnewall.com> CC: Stephen Hemminger <stephen@...workplumber.org>, Netdev <netdev@...r.kernel.org>, netfilter-devel@...r.kernel.org, bridge@...ts.linux-foundation.org Subject: Re: Revert 462fb2af9788a82a534f8184abfde31574e1cfa0 (bridge : Sanitize skb before it enters the IP stack) Florian Westphal schreef op 19/05/2014 19:09: > David Newall <davidn@...idnewall.com> wrote: > > [ remove lkml and cc nf-devel ] > >> I tried to persevere with the commit: I recalculated checksum, which >> left routes and times improperly updated in options. Then I tried >> calling ip_forward_options, which looks like it would correctly >> update RR and TS (not to mention checksum)m but that bombed because >> skb_rtable returned NULL. > > Yes. bridge<->netfilter wiring is pure duct tape. > The glue code will set up a fake rtable for the skb after the > prerouting hook. [ see br_nf_pre_routing_finish() ]. > >> I see three ways to progress: >> >> 1. Possibly call ip_forward_option, but that requires somebody who >> understands this code to help; >> 2. Just recalculate the checksum, leaving crap in the options; or >> 3. Revert the commit. > > I think none of these are an option. > > I fail to understand why a bridge should honor/modifiy IP options. > > For the 'local delivery' case the ip stack will take care of > option parsing, for forwarding it should be sufficient to do > sanity tests (for netfilters sake). > >>>From a quick glance, it should be sufficient to edit > br_parse_ip_options() and remove everything after > > memset(IPCB(skb), 0, sizeof(struct inet_skb_parm)); > > A 2nd step would be to move a copy of ip_options_compile() > into br_netfilter.c and trim it down to only validate the > ipv4 header without modifying it. Perhaps it's possible to call ip_options_compile with a skb == NULL, like ip_options.c::ip_options_get_finish does. That way we don't need to duplicate code. An alternative would be to make sure that the data pointed to by IPCB and BR_INPUT_SKB_CB don't overlap. If this were the case, we could indeed just revert the commit that was referred to. cheers, Bart -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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