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

[Eric Dumazet <eric.dumazet@gmail.com>]

Le jeudi 26 août 2010 à 10:03 +0200, Eric Dumazet a écrit :
> 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(-)
> 
> 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);
> 

Hmm, reading this code again, I suspect a much better fix is to make
sure 'ethernet header' is in skb head, not in a fragment.

Maybe frame is valid but only L2TP encapsulation in skb->header at this
point.

Thanks !

[PATCH] l2tp: test for ethernet header 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 head contains
at least an ethernet header, even if length included in upper layer said
so. Use pskb_may_pull() to make sure this ethernet header is present in
skb head.

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_eth.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/l2tp/l2tp_eth.c b/net/l2tp/l2tp_eth.c
index 58c6c4c..1ae6976 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 (!pskb_may_pull(skb, sizeof(ETH_HLEN)))
 		goto error;
 
 	secpath_reset(skb);