netdev - Re: [PATCH net-next] net: keep original skb which only needs header checking during software GSO

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Date:	Fri, 19 Sep 2014 15:49:34 +0800
From:	Jason Wang <jasowang@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	davem@...emloft.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] net: keep original skb which only needs header
 checking during software GSO

On 09/19/2014 03:04 PM, Eric Dumazet wrote:
> On Fri, 2014-09-19 at 14:38 +0800, Jason Wang wrote:
>> Commit ce93718fb7cdbc064c3000ff59e4d3200bdfa744 ("net: Don't keep
>> around original SKB when we software segment GSO frames") frees the
>> original skb after software GSO even for dodgy gso skbs. This breaks
>> the stream throughput from untrusted sources, since only header
>> checking was done during software GSO instead of a true
>> segmentation. This patch fixes this by freeing the original gso skb
>> only when it was really segmented by software.
>>
>> Fixes ce93718fb7cdbc064c3000ff59e4d3200bdfa744 ("net: Don't keep
>> around original SKB when we software segment GSO frames.")
>>
>> CC: David S. Miller <davem@...emloft.net>
>> Signed-off-by: Jason Wang <jasowang@...hat.com>
>> ---
>>  net/core/dev.c | 6 ++++--
>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index e916ba8..b7a0e1d 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -2694,10 +2694,12 @@ struct sk_buff *validate_xmit_skb(struct sk_buff *skb, struct net_device *dev)
>>  		struct sk_buff *segs;
>>  
>>  		segs = skb_gso_segment(skb, features);
>> -		kfree_skb(skb);
>>  		if (IS_ERR(segs))
>>  			
>> -		skb = segs;
>> +		else if (segs) {
>> +			kfree_skb(skb);
>> +			skb = segs;
>> +		}
>>  	} else {
>>  		if (skb_needs_linearize(skb, features) &&
>>  		    __skb_linearize(skb))
> Good catch !
>
> While we are at it, could you use consume_skb() instead of kfree_skb(),
> and add missing {} (CodingStyle) ?
>
> if (IS_ERR(segs)) {
> 	segs = NULL;
> } else if (segs) {
> 	consume_skb(skb);
> 	skb = segs;
> }
>
>
> Thanks !
>
>

Yes, it's better. Will do them in V2.
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