Subject: Re: [PATCH] sctp: Make "Invalid Stream Identifier" ERROR follows SACK when bundling

From: xufeng zhang <[email-masked]>
Date: Tue, 24 Jul 2012 11:02:47 +0800

On 07/24/2012 10:27 AM, Vlad Yasevich wrote:
> xufeng zhang<[email-masked]>  wrote:
>
>    
>> On 07/19/2012 01:57 PM, [email-masked] wrote:
>>      
>>> When "Invalid Stream Identifier" ERROR happens after process the
>>> received DATA chunks, this ERROR chunk is enqueued into outqueue
>>> before SACK chunk, so when bundling ERROR chunk with SACK chunk,
>>> the ERROR chunk is always placed first in the packet because of
>>> the chunk's position in the outqueue.
>>> This violates sctp specification:
>>>       RFC 4960 6.5. Stream Identifier and Stream Sequence Number
>>>       ...The endpoint may bundle the ERROR chunk in the same
>>>       packet as the SACK as long as the ERROR follows the SACK.
>>> So we must place SACK first when bundling "Invalid Stream Identifier"
>>> ERROR and SACK in one packet.
>>> Although we can do that by enqueue SACK chunk into outqueue before
>>> ERROR chunk, it will violate the side-effect interpreter processing.
>>> It's easy to do this job when dequeue chunks from the outqueue,
>>> by this way, we introduce a flag 'has_isi_err' which indicate
>>> whether or not the "Invalid Stream Identifier" ERROR happens.
>>>
>>> Signed-off-by: Xufeng Zhang<[email-masked]>
>>> ---
>>>    include/net/sctp/structs.h |    2 ++
>>>    net/sctp/output.c          |   26 ++++++++++++++++++++++++++
>>>    2 files changed, 28 insertions(+), 0 deletions(-)
>>>
>>> diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
>>> index 88949a9..5adf4de 100644
>>> --- a/include/net/sctp/structs.h
>>> +++ b/include/net/sctp/structs.h
>>> @@ -842,6 +842,8 @@ struct sctp_packet {
>>>    	    has_sack:1,		/* This packet contains a SACK chunk. */
>>>    	    has_auth:1,		/* This packet contains an AUTH chunk */
>>>    	    has_data:1,		/* This packet contains at least 1 DATA chunk */
>>> +	    has_isi_err:1,	/* This packet contains a "Invalid Stream
>>> +				 * Identifier" ERROR chunk */
>>>    	    ipfragok:1,		/* So let ip fragment this packet */
>>>    	    malloced:1;		/* Is it malloced? */
>>>    };
>>> diff --git a/net/sctp/output.c b/net/sctp/output.c
>>> index 817174e..77fb1ae 100644
>>> --- a/net/sctp/output.c
>>> +++ b/net/sctp/output.c
>>> @@ -79,6 +79,7 @@ static void sctp_packet_reset(struct sctp_packet
>>>        
>> *packet)
>>      
>>>    	packet->has_sack = 0;
>>>    	packet->has_data = 0;
>>>    	packet->has_auth = 0;
>>> +	packet->has_isi_err = 0;
>>>    	packet->ipfragok = 0;
>>>    	packet->auth = NULL;
>>>    }
>>> @@ -267,6 +268,7 @@ static sctp_xmit_t sctp_packet_bundle_sack(struct
>>>        
>> sctp_packet *pkt,
>>      
>>>    sctp_xmit_t sctp_packet_append_chunk(struct sctp_packet *packet,
>>>    				     struct sctp_chunk *chunk)
>>>    {
>>> +	struct sctp_chunk *lchunk;
>>>    	sctp_xmit_t retval = SCTP_XMIT_OK;
>>>    	__u16 chunk_len = WORD_ROUND(ntohs(chunk->chunk_hdr->length));
>>>
>>> @@ -316,7 +318,31 @@ sctp_xmit_t sctp_packet_append_chunk(struct
>>>        
>> sctp_packet *packet,
>>      
>>>    		packet->has_cookie_echo = 1;
>>>    		break;
>>>
>>> +	    case SCTP_CID_ERROR:
>>> +		if (chunk->subh.err_hdr->cause&   SCTP_ERROR_INV_STRM)
>>> +			packet->has_isi_err = 1;
>>> +		break;
>>> +
>>>    	    case SCTP_CID_SACK:
>>> +		/* RFC 4960
>>> +		 * 6.5 Stream Identifier and Stream Sequence Number
>>> +		 * The endpoint may bundle the ERROR chunk in the same
>>> +		 * packet as the SACK as long as the ERROR follows the SACK.
>>> +		 */
>>> +		if (packet->has_isi_err) {
>>> +			if (list_is_singular(&packet->chunk_list))
>>> +				list_add(&chunk->list,&packet->chunk_list);
>>> +			else {
>>> +				lchunk = list_first_entry(&packet->chunk_list,
>>> +						struct sctp_chunk, list);
>>> +				list_add(&chunk->list,&lchunk->list);
>>> +			}
>>>
>>>        
>> And I should clarify the above judgment code.
>> AFAIK, there should be two cases for the bundling when invalid stream
>> identifier error happens:
>> 1). COOKIE_ACK ERROR SACK
>> 2). ERROR SACK
>> So I need to deal with the two cases differently.
>>
>>      
> Sorry but I just don't buy that the above are the only 2 cases.  What if there are addip chunks as well?  What if there are some other extensions also.  This code has to be generic enough to handle any condition.
>    
Aha, you are right, this may happens.
So I think the general solution is to fix this problem in the enqueue side.
What do you think? any better suggestion!

Thanks,
Xufeng Zhang
> - vlad
>
>    
>> Thanks,
>> Xufeng Zhang
>>      
>>> +			packet->size += chunk_len;
>>> +			chunk->transport = packet->transport;
>>> +			packet->has_sack = 1;
>>> +			goto finish;
>>> +		}
>>> +
>>>    		packet->has_sack = 1;
>>>    		break;
>>>
>>>
>>>        
>
>