Subject: Re: [PATCH] tcp_output: Re: rare bad TCP checksum with 2.6.19?

From: Michael Tokarev <[email-masked]>
Date: Fri, 19 Jan 2007 16:23:19 +0300

Patrick McHardy wrote:
> Jarek Poplawski wrote:
>> Here is my patch proposal. If I'm not totally wrong,
>> there is a possibility that, during collapsing, empty
>> skb with FIN is added to "normal" packet and changes
>> its ip_summed field to CHECKSUM_NONE.
>>
>> diff -Nurp linux-2.6.19-/net/ipv4/tcp_output.c linux-2.6.19/net/ipv4/tcp_output.c
>> --- linux-2.6.19-/net/ipv4/tcp_output.c	2006-11-29 22:57:37.000000000 +0100
>> +++ linux-2.6.19/net/ipv4/tcp_output.c	2007-01-19 07:58:39.000000000 +0100
>> @@ -1590,7 +1590,8 @@ static void tcp_retrans_try_collapse(str
>>  
>>  		memcpy(skb_put(skb, next_skb_size), next_skb->data, next_skb_size);
>>  
>> -		skb->ip_summed = next_skb->ip_summed;
>> +		if (next_skb->ip_summed == CHECKSUM_PARTIAL)
>> +			skb->ip_summed = CHECKSUM_PARTIAL;
>>  
>>  		if (skb->ip_summed != CHECKSUM_PARTIAL)
>>  			skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
>>
> 
> I noticed this too, but I can't see how it could lead to
> a partial checksum on the wire since the checksumming is
> done after changing ip_summed to CHECKSUM_NONE. Is this
> patch verified to fix Michael's problem?

It seems to fix this "my" problem, yes - at least I can't reproduce it anymore.
Tcpdump is running however - let's see... :)

/mjt