Messages in this thread | | | Date | Sat, 09 Jul 2016 11:48:49 +0200 | From | Daniel Borkmann <> | Subject | Re: [PATCH net] udp: prevent bugcheck if filter truncates packet too much |
| |
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.gra@gmail.com> >>> Signed-off-by: Michal Kubecek <mkubecek@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 <edumazet@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.
| |