[Bugme-new,Bug,16529] New: xennet driver crashes when using with pseudowire aka l2tpv3

Here is the patch, could you test it please ?

Thanks !

[PATCH] l2tp: test for malicious frames in l2tp_eth_dev_recv()

close https://bugzilla.kernel.org/show_bug.cgi?id=16529

Before calling dev_forward_skb(), we should make sure skb contains at
least an ethernet header, even if length included in upper layer said
so.

Reported-by: Thomas Heil <heil@terminal-consulting.de>
Reported-by: Ian Campbell <Ian.Campbell@eu.citrix.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
---
 net/l2tp/l2tp_core.c |    2 +-
 net/l2tp/l2tp_eth.c  |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)



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On Thu, 2010-08-26 at 09:03 +0100, Eric Dumazet wrote:
> Here is the patch, could you test it please ?
> 
> Thanks !
> 
> [PATCH] l2tp: test for malicious frames in l2tp_eth_dev_recv()
> 
> close https://bugzilla.kernel.org/show_bug.cgi?id=16529
> 
> Before calling dev_forward_skb(), we should make sure skb contains at
> least an ethernet header, even if length included in upper layer said
> so.

Does this imply that there is some problem with xen-netfront setting
skb->len or skb->data_len or something incorrectly? It's not clear where
data_len has come from in this context.

Ian.

> 
> Reported-by: Thomas Heil <heil@terminal-consulting.de>
> Reported-by: Ian Campbell <Ian.Campbell@eu.citrix.com>
> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
> ---
>  net/l2tp/l2tp_core.c |    2 +-
>  net/l2tp/l2tp_eth.c  |    2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/l2tp/l2tp_eth.c b/net/l2tp/l2tp_eth.c
> index 58c6c4c..0687c5c 100644
> --- a/net/l2tp/l2tp_eth.c
> +++ b/net/l2tp/l2tp_eth.c
> @@ -132,7 +132,7 @@ static void l2tp_eth_dev_recv(struct l2tp_session *session, struct sk_buff *skb,
>  		printk("\n");
>  	}
>  
> -	if (data_len < ETH_HLEN)
> +	if (skb->len < ETH_HLEN)
>  		goto error;
>  
>  	secpath_reset(skb);
> 
> 


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Le jeudi 26 août 2010 à 09:14 +0100, Ian Campbell a écrit :
> On Thu, 2010-08-26 at 09:03 +0100, Eric Dumazet wrote:
> > Here is the patch, could you test it please ?
> > 
> > Thanks !
> > 
> > [PATCH] l2tp: test for malicious frames in l2tp_eth_dev_recv()
> > 
> > close https://bugzilla.kernel.org/show_bug.cgi?id=16529
> > 
> > Before calling dev_forward_skb(), we should make sure skb contains at
> > least an ethernet header, even if length included in upper layer said
> > so.
> 
> Does this imply that there is some problem with xen-netfront setting
> skb->len or skb->data_len or something incorrectly? It's not clear where
> data_len has come from in this context.

data_len is a 16bit field provided in a prior encapsulation header,
provided by user (untrusted source)

Some buggy or malicious software sent an invalid frame,


< encapsulation [len=1000] >  < 'runt' eth frame (len<14) > 

Another fix would be to change l2tp_recv_dequeue_skb(), and check

L2TP_SKB_CB(skb)->length against skb->len, before calling 

(*session->recv_skb)(session, skb, length);


I prefer the one liner patch I sent you, as a minimum fix.


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On Thu, 2010-08-26 at 09:34 +0100, Eric Dumazet wrote:
> Le jeudi 26 août 2010 à 09:14 +0100, Ian Campbell a écrit :
> > On Thu, 2010-08-26 at 09:03 +0100, Eric Dumazet wrote:
> > > Here is the patch, could you test it please ?
> > > 
> > > Thanks !
> > > 
> > > [PATCH] l2tp: test for malicious frames in l2tp_eth_dev_recv()
> > > 
> > > close https://bugzilla.kernel.org/show_bug.cgi?id=16529
> > > 
> > > Before calling dev_forward_skb(), we should make sure skb contains at
> > > least an ethernet header, even if length included in upper layer said
> > > so.
> > 
> > Does this imply that there is some problem with xen-netfront setting
> > skb->len or skb->data_len or something incorrectly? It's not clear where
> > data_len has come from in this context.
> 
> data_len is a 16bit field provided in a prior encapsulation header,
> provided by user (untrusted source)
> 
> Some buggy or malicious software sent an invalid frame,
> 
> 
> < encapsulation [len=1000] >  < 'runt' eth frame (len<14) > 
> 
> Another fix would be to change l2tp_recv_dequeue_skb(), and check
> 
> L2TP_SKB_CB(skb)->length against skb->len, before calling 
> 
> (*session->recv_skb)(session, skb, length);
> 
> 
> I prefer the one liner patch I sent you, as a minimum fix.

Thanks, I just wanted to be sure we weren't papering over a potential
issue in xen-netfront.

Ian.


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