From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tim Hartrick Subject: Re: Crash in ip_expire/icmp_send - 2.6.38.2 (Ubuntu 11.04 natty) Date: Tue, 27 Dec 2011 21:41:07 -0700 Message-ID: <1325047267.4354.21.camel@boudreau> References: <1325043141.4354.20.camel@boudreau> <20111227.224853.1945641698257880843.davem@davemloft.net> Reply-To: tim@edgecast.com Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org To: David Miller Return-path: Received: from mail-iy0-f174.google.com ([209.85.210.174]:52988 "EHLO mail-iy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753253Ab1L1ElR (ORCPT ); Tue, 27 Dec 2011 23:41:17 -0500 Received: by iaeh11 with SMTP id h11so21418726iae.19 for ; Tue, 27 Dec 2011 20:41:17 -0800 (PST) In-Reply-To: <20111227.224853.1945641698257880843.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-ID: David, Thanks for the pointer to the patch. I will endeavor to obey the protocol in the future. Tim Hartrick On Tue, 2011-12-27 at 22:48 -0500, David Miller wrote: > Well known and fixed a long time ago, see the patch below. > > Please reproduce bugs against current upstream kernels before > reporting the problem here, if it only occurs in the vendor's > kernel then the appropriate thing to do is to report it to > the vendor. > > -------------------- > commit 64f3b9e203bd06855072e295557dca1485a2ecba > Author: Eric Dumazet > Date: Wed May 4 10:02:26 2011 +0000 > > net: ip_expire() must revalidate route > > Commit 4a94445c9a5c (net: Use ip_route_input_noref() in input path) > added a bug in IP defragmentation handling, in case timeout is fired. > > When a frame is defragmented, we use last skb dst field when building > final skb. Its dst is valid, since we are in rcu read section. > > But if a timeout occurs, we take first queued fragment to build one ICMP > TIME EXCEEDED message. Problem is all queued skb have weak dst pointers, > since we escaped RCU critical section after their queueing. icmp_send() > might dereference a now freed (and possibly reused) part of memory. > > Calling skb_dst_drop() and ip_route_input_noref() to revalidate route is > the only possible choice. > > Reported-by: Denys Fedoryshchenko > Signed-off-by: Eric Dumazet > Signed-off-by: David S. Miller > > diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c > index a1151b8..b1d282f 100644 > --- a/net/ipv4/ip_fragment.c > +++ b/net/ipv4/ip_fragment.c > @@ -223,31 +223,30 @@ static void ip_expire(unsigned long arg) > > if ((qp->q.last_in & INET_FRAG_FIRST_IN) && qp->q.fragments != NULL) { > struct sk_buff *head = qp->q.fragments; > + const struct iphdr *iph; > + int err; > > rcu_read_lock(); > head->dev = dev_get_by_index_rcu(net, qp->iif); > if (!head->dev) > goto out_rcu_unlock; > > + /* skb dst is stale, drop it, and perform route lookup again */ > + skb_dst_drop(head); > + iph = ip_hdr(head); > + err = ip_route_input_noref(head, iph->daddr, iph->saddr, > + iph->tos, head->dev); > + if (err) > + goto out_rcu_unlock; > + > /* > - * Only search router table for the head fragment, > - * when defraging timeout at PRE_ROUTING HOOK. > + * Only an end host needs to send an ICMP > + * "Fragment Reassembly Timeout" message, per RFC792. > */ > - if (qp->user == IP_DEFRAG_CONNTRACK_IN && !skb_dst(head)) { > - const struct iphdr *iph = ip_hdr(head); > - int err = ip_route_input(head, iph->daddr, iph->saddr, > - iph->tos, head->dev); > - if (unlikely(err)) > - goto out_rcu_unlock; > - > - /* > - * Only an end host needs to send an ICMP > - * "Fragment Reassembly Timeout" message, per RFC792. > - */ > - if (skb_rtable(head)->rt_type != RTN_LOCAL) > - goto out_rcu_unlock; > + if (qp->user == IP_DEFRAG_CONNTRACK_IN && > + skb_rtable(head)->rt_type != RTN_LOCAL) > + goto out_rcu_unlock; > > - } > > /* Send an ICMP "Fragment Reassembly Timeout" message. */ > icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);