Re: [PATCH][v2] dev : fix mtu check when TSO is enabled

[Daniel Lezcano <daniel.lezcano@free.fr>]

On 03/14/2011 09:02 PM, Eric Dumazet wrote:
> Le lundi 14 mars 2011 à 20:10 +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<daniel.lezcano@free.fr>
>> Cc: Eric Dumazet<eric.dumazet@gmail.com>
>> Cc: Patrick McHardy<kaber@trash.net>
>> Cc: Andrian Nord<nightnord@gmail.com>
>> ---
>>   net/core/dev.c |   24 ++++++++++++++++++++++--
>>   1 files changed, 22 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index 6561021..f1607a0 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -1503,6 +1503,27 @@ static inline void net_timestamp_check(struct sk_buff *skb)
>>   		__net_timestamp(skb);
>>   }
>>
>> +static inline bool is_skb_forwardable(struct net_device *dev,
>> +				      struct sk_buff *skb)
>> +{
>> +	unsigned int len;
>> +
>> +	if (!dev->flags&  IFF_UP)
>> +		return false;
> 	if (!(dev->flags&  IFF_UP))
> 		return false;

Argh ! Hopefully you saw it.

>> +
>> +	/* we should not check the mtu size if TSO is enabled otherwise
>> +	 * we may have a packet with a length bigger than the expected
>> +	 * one as it was not segmented before */
>> +	if (skb->dev&&  skb->dev->features&  NETIF_F_TSO)
>> +		return true;
>> +
>> +	len = dev->mtu + dev->hard_header_len + VLAN_HLEN;
>> +	if (skb->len>  len)
>> +		return false;
>> +
> I suggest you reorder tests so that the first one is discriminant most
> of the time
>
> 	maxlen = dev->mtu + dev->hard_header_len + VLAN_HLEN;
> 	if (skb->len<  maxlen)
> 		return true;
> 	
> 	if (skb->dev&&  skb->dev->features&  NETIF_F_TSO)
> 		return true;
>
> 	return false;

Ok. Thanks !

   -- Daniel