Recently had a bug reported to me, in which the user was sending
packets with a payload containing a sequence number. The packets
were getting delivered in order according the chunk TSN values, but
the sequence values in the payload were arriving out of order. At
first I thought it must be an application error, but we eventually
found it to be a problem on the transmit side in the sctp stack.
The conditions for the error are that multihoming must be in use,
and it helps if each transport has a different pmtu. The problem
occurs in sctp_outq_flush. Basically we dequeue packets from the
data queue, and attempt to append them to the orrered packet for a
given transport. After we append a data chunk we add the trasport
to the end of a list of transports to have their packets sent at
the end of sctp_outq_flush. The problem occurs when a data chunks
fills up a offered packet on a transport. The function that does
the appending (sctp_packet_transmit_chunk), will try to call
sctp_packet_transmit on the full packet, and then append the chunk
to a new packet. This call to sctp_packet_transmit, sends that
packet ahead of the others that may be queued in the transport_list
in sctp_outq_flush. The result is that frames that were sent in one
order from the user space sending application get re-ordered prior
to tsn assignment in sctp_packet_transmit, resulting in mis-sequencing
of data payloads, even though tsn ordering is correct.
The fix is to change where we assign a tsn. By doing this earlier,
we are then free to place chunks in packets, whatever way we
see fit and the protocol will make sure to do all the appropriate
re-ordering on receive as is needed.
Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
Reported-by: William Reich <reich@ulticom.com>
Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
d8dd15781d