On Sat, Jul 09, 2016 at 11:48:49AM +0200, Daniel Borkmann wrote: > On 07/09/2016 02:20 AM, Alexei Starovoitov wrote: > >On Sat, Jul 09, 2016 at 01:31:40AM +0200, Eric Dumazet wrote: > >>On Fri, 2016-07-08 at 17:52 +0200, Michal Kubecek wrote: > >>>If socket filter truncates an udp packet below the length of UDP header > >>>in udpv6_queue_rcv_skb() or udp_queue_rcv_skb(), it will trigger a > >>>BUG_ON in skb_pull_rcsum(). This BUG_ON (and therefore a system crash if > >>>kernel is configured that way) can be easily enforced by an unprivileged > >>>user which was reported as CVE-2016-6162. For a reproducer, see > >>>http://seclists.org/oss-sec/2016/q3/8 > >>> > >>>Fixes: e6afc8ace6dd ("udp: remove headers from UDP packets before > >>>queueing") > >>>Reported-by: Marco Grassi <marco....@gmail.com> > >>>Signed-off-by: Michal Kubecek <mkube...@suse.cz> > >>>--- > >>> net/ipv4/udp.c | 2 ++ > >>> net/ipv6/udp.c | 2 ++ > >>> 2 files changed, 4 insertions(+) > >>> > >>>diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c > >>>index ca5e8ea29538..4aed8fc23d32 100644 > >>>--- a/net/ipv4/udp.c > >>>+++ b/net/ipv4/udp.c > >>>@@ -1583,6 +1583,8 @@ int udp_queue_rcv_skb(struct sock *sk, struct > >>>sk_buff *skb) > >>> > >>> if (sk_filter(sk, skb)) > >>> goto drop; > >>>+ if (unlikely(skb->len < sizeof(struct udphdr))) > >>>+ goto drop; > >>> > >>> udp_csum_pull_header(skb); > >>> if (sk_rcvqueues_full(sk, sk->sk_rcvbuf)) { > >>>diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c > >>>index 005dc82c2138..acc09705618b 100644 > >>>--- a/net/ipv6/udp.c > >>>+++ b/net/ipv6/udp.c > >>>@@ -620,6 +620,8 @@ int udpv6_queue_rcv_skb(struct sock *sk, struct > >>>sk_buff *skb) > >>> > >>> if (sk_filter(sk, skb)) > >>> goto drop; > >>>+ if (unlikely(skb->len < sizeof(struct udphdr))) > >>>+ goto drop; > >>> > >>> udp_csum_pull_header(skb); > >>> if (sk_rcvqueues_full(sk, sk->sk_rcvbuf)) { > >> > >> > >>Arg :( > >> > >>Acked-by: Eric Dumazet <eduma...@google.com> > > > >this is incomplete fix. Please do not apply. See discussion at > >security@kernel > > Ohh well, didn't see it earlier before starting the discussion at security@... > > I'm okay if we take this for now as a quick band aid and find a better > way how to deal with the underlying issue long-term so that it's > /guaranteed/ that it doesn't bite us any further in such fragile ways.
Agreed. As rc7 is due in a day or two, rushing a complex and intrusive solution in might be too risky. Michal Kubecek
