NACK.

If the INIT-ACK chunk is too short to contain the init-tag, get the 
init-tag of peer may get a unexpected value.
Such as this:
  CHUNK_INIT_ACK
   Type                             = 2
   Flags                            = 0
   Length                           = 4

So I think the better way is to set T bit of ABORT chunk and used the 
own's Tag.

Regards.
Wei Yongjun

Gui Jianfeng wrote:
quoted text
> Hi Vlad,
> When kernel receives a INIT ACK which has an invalid length, it replies a 0 VerificationTag ABORT.
> This violates sctp protocol apparently, and doesn't comply to RFC requirement. VerificationTag 
> is allowed to set to 0 only in INIT Chunk packet.
> We need to record the VerificationTag from INIT ACK before sending out the ABORT Chunk.
>
> Here is a patch for fixing this bug.
>
> Signed-off-by: Guijianfeng <guijianfeng@cn.fujitsu.com>
> ---
>  include/net/sctp/command.h |    1 +
>  net/sctp/sm_sideeffect.c   |    5 ++++-
>  net/sctp/sm_statefuns.c    |    9 +++++++++
>  3 files changed, 14 insertions(+), 1 deletions(-)
>
> diff --git a/include/net/sctp/command.h b/include/net/sctp/command.h
> index 10ae2da..35b1e83 100644
> --- a/include/net/sctp/command.h
> +++ b/include/net/sctp/command.h
> @@ -104,6 +104,7 @@ typedef enum {
>  	SCTP_CMD_ADAPTATION_IND, /* generate and send adaptation event */
>  	SCTP_CMD_ASSOC_SHKEY,    /* generate the association shared keys */
>  	SCTP_CMD_T1_RETRAN,	 /* Mark for retransmission after T1 timeout  */
> +	SCTP_CMD_UPDATE_INITTAG, /* Update peer inittag */
>  	SCTP_CMD_LAST
>  } sctp_verb_t;
>  
> diff --git a/net/sctp/sm_sideeffect.c b/net/sctp/sm_sideeffect.c
> index 28eb38e..2dbc7bd 100644
> --- a/net/sctp/sm_sideeffect.c
> +++ b/net/sctp/sm_sideeffect.c
> @@ -1536,7 +1536,10 @@ static int sctp_cmd_interpreter(sctp_event_t event_type,
>  			error = sctp_auth_asoc_init_active_key(asoc,
>  						GFP_ATOMIC);
>  			break;
> -
> +		case SCTP_CMD_UPDATE_INITTAG:
> +			asoc->peer.i.init_tag = cmd->obj.u32;
> +			break;
> +			
>  		default:
>  			printk(KERN_WARNING "Impossible command: %u, %p\n",
>  			       cmd->verb, cmd->obj.ptr);
> diff --git a/net/sctp/sm_statefuns.c b/net/sctp/sm_statefuns.c
> index f2ed647..1bc2c49 100644
> --- a/net/sctp/sm_statefuns.c
> +++ b/net/sctp/sm_statefuns.c
> @@ -4144,6 +4144,15 @@ static sctp_disposition_t sctp_sf_abort_violation(
>  		goto nomem;
>  
>  	if (asoc) {
> +		/* Treat INIT-ACK as a special case. */
> +		if (chunk->chunk_hdr->type == SCTP_CID_INIT_ACK) {
> +			sctp_initack_chunk_t *initack;
> +
> +			initack = (sctp_initack_chunk_t *)chunk->chunk_hdr;
> +			sctp_add_cmd_sf(commands, SCTP_CMD_UPDATE_INITTAG,
> +					SCTP_U32(ntohl(initack->init_hdr.init_tag)));
> +		}
> +
>  		sctp_add_cmd_sf(commands, SCTP_CMD_REPLY, SCTP_CHUNK(abort));
>  		SCTP_INC_STATS(SCTP_MIB_OUTCTRLCHUNKS);
>   
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