[PATCH net] udp: prevent bugcheck if filter truncates packet too much

[PATCH net] udp: prevent bugcheck if filter truncates packet too much

[Michal Kubecek]

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)) {
-- 
2.9.0

Re: [PATCH net] udp: prevent bugcheck if filter truncates packet too much

[Eric Dumazet]

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>

Thanks !

Re: [PATCH net] udp: prevent bugcheck if filter truncates packet too much

[Alexei Starovoitov]

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

Re: [PATCH net] udp: prevent bugcheck if filter truncates packet too much

[Daniel Borkmann]

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.

Re: [PATCH net] udp: prevent bugcheck if filter truncates packet too much

[Michal Kubecek]

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.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.

Agreed. As rc7 is due in a day or two, rushing a complex and intrusive
solution in might be too risky.

Michal Kubecek

Re: [PATCH net] udp: prevent bugcheck if filter truncates packet too much

[Willem de Bruijn]

On Sat, Jul 9, 2016 at 6:43 AM, Michal Kubecek <mkubecek@suse.cz> wrote:
> 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.gra@gmail.com>
>> >>>Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
>> >>>---
>
>> >>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.
>
> Agreed. As rc7 is due in a day or two, rushing a complex and intrusive
> solution in might be too risky.

Acked-by: Willem de Bruijn <willemb@google.com>

Thanks, Michal.

Re: [PATCH net] udp: prevent bugcheck if filter truncates packet too much

[David Miller]

From: Michal Kubecek <mkubecek@suse.cz>
Date: Fri,  8 Jul 2016 17:52:33 +0200 (CEST)

> 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>

Applied and queued up for -stable, thanks.