| Message ID | 1327587245-1488-2-git-send-email-apw@canonical.com |
|---|---|
| State | New |
| Headers | show |
On 26.01.2012 15:14, Andy Whitcroft wrote: > From: Eric Dumazet <eric.dumazet@gmail.com> > > 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 <denys@visp.net.lb> > Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> > Signed-off-by: David S. Miller <davem@davemloft.net> > > (cherry picked from commit 64f3b9e203bd06855072e295557dca1485a2ecba) > CVE-2011-1927 > BugLink: http://bugs.launchpad.net/bugs/922051 > Signed-off-by: Andy Whitcroft <apw@canonical.com> > --- > net/ipv4/ip_fragment.c | 33 ++++++++++++++++----------------- > 1 files changed, 16 insertions(+), 17 deletions(-) > > diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c > index 75347ea..cbc6571 100644 > --- a/net/ipv4/ip_fragment.c > +++ b/net/ipv4/ip_fragment.c > @@ -207,31 +207,30 @@ 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); Looks to be doing as claimed and actually is a cherry pick Acked-by: Stefan Bader <smb@canonical.com>
diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c index 75347ea..cbc6571 100644 --- a/net/ipv4/ip_fragment.c +++ b/net/ipv4/ip_fragment.c @@ -207,31 +207,30 @@ 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);