Subject: Re: [PATCH 2/2] dev : fix mtu check when TSO is enabled

From: Daniel Lezcano <[email-masked]>
Date: Mon, 14 Mar 2011 20:00:43 +0100

On 03/14/2011 06:01 PM, Eric Dumazet wrote:
> Le lundi 14 mars 2011 à 17:08 +0100, Daniel Lezcano a écrit :
>> In case the device where is coming from the packet has TSO enabled,
>> we should not check the mtu size value as this one could be bigger
>> than the expected value.
>>
>> This is the case for the macvlan driver when the lower device has
>> TSO enabled. The macvlan inherit this feature and forward the packets
>> without fragmenting them. Then the packets go through dev_forward_skb
>> and are dropped. This patch fix this by checking TSO is not enabled
>> when we want to check the mtu size.
>>
>> Signed-off-by: Daniel Lezcano<[email-masked]>
>> Cc: Patrick McHardy<[email-masked]>
>> Cc: Andrian Nord<[email-masked]>
>> ---
>>   net/core/dev.c |    6 ++++--
>>   1 files changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index 6561021..010a0a9 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -1526,8 +1526,10 @@ int dev_forward_skb(struct net_device *dev, struct sk_buff *skb)
>>   	skb_orphan(skb);
>>   	nf_reset(skb);
>>
>> -	if (unlikely(!(dev->flags&  IFF_UP) ||
>> -		     (skb->len>  (dev->mtu + dev->hard_header_len + VLAN_HLEN)))) {
>> +	if (unlikely(!(skb->dev->features&  NETIF_F_TSO)&&
>
> Sorry, this needs a comment at least, or even better a helper function
> on its own.
>
> We test both skb->dev&  dev, pointing to different devices, this is
> really error prone.
>
> Are we sure all callers set skb->dev before calling  dev_forward_skb() ?

Thanks Eric for the comments, I will resend a new version.

   -- Daniel