TCP_STATE_SENT ( TCP_FIN ) ) ) \
== TCP_STATE_ACKED ( TCP_SYN ) )
+/** Have ever been fully established
+ *
+ * We have been fully established if we have both received a SYN and
+ * had our own SYN acked.
+ */
+#define TCP_HAS_BEEN_ESTABLISHED(state) \
+ ( ( (state) & ( TCP_STATE_ACKED ( TCP_SYN ) | \
+ TCP_STATE_RCVD ( TCP_SYN ) ) ) \
+ == ( TCP_STATE_ACKED ( TCP_SYN ) | TCP_STATE_RCVD ( TCP_SYN ) ) )
+
/** Have closed gracefully
*
* We have closed gracefully if we have both received a FIN and had
size_t len;
unsigned int acked_flags;
- /* Ignore duplicate or out-of-range ACK */
- if ( ack_len > tcp->snd_sent ) {
- DBGC ( tcp, "TCP %p received ACK for [%08x,%08zx), "
- "sent only [%08x,%08x)\n", tcp, tcp->snd_seq,
- ( tcp->snd_seq + ack_len ), tcp->snd_seq,
- ( tcp->snd_seq + tcp->snd_sent ) );
- return -EINVAL;
- }
-
- /* Acknowledge any flags being sent */
+ /* Determine acknowledged flags and data length */
len = ack_len;
acked_flags = ( TCP_FLAGS_SENDING ( tcp->tcp_state ) &
( TCP_SYN | TCP_FIN ) );
if ( acked_flags )
len--;
+ /* Stop retransmission timer if necessary */
+ if ( ack_len == 0 ) {
+ /* Duplicate ACK (or just a packet that isn't
+ * intending to ACK any new data). If the
+ * retransmission timer is running, leave it running
+ * so that we don't immediately retransmit and cause a
+ * sorceror's apprentice syndrome.
+ */
+ } else if ( ack_len <= tcp->snd_sent ) {
+ /* ACK of new data. Stop the retransmission timer. */
+ stop_timer ( &tcp->timer );
+ } else {
+ /* Out-of-range (or old duplicate) ACK. Leave the
+ * timer running, as for the ack_len==0 case, to
+ * handle old duplicate ACKs.
+ */
+ DBGC ( tcp, "TCP %p received ACK for [%08x,%08zx), "
+ "sent only [%08x,%08x)\n", tcp, tcp->snd_seq,
+ ( tcp->snd_seq + ack_len ), tcp->snd_seq,
+ ( tcp->snd_seq + tcp->snd_sent ) );
+ /* Send RST if an out-of-range ACK is received on a
+ * not-yet-established connection.
+ */
+ if ( ! TCP_HAS_BEEN_ESTABLISHED ( tcp->tcp_state ) )
+ return -EINVAL;
+ }
+
/* Update SEQ and sent counters, and window size */
tcp->snd_seq = ack;
tcp->snd_sent = 0;
tcp->snd_win = win;
- /* Stop the retransmission timer */
- stop_timer ( &tcp->timer );
-
/* Remove any acknowledged data from transmit queue */
tcp_process_queue ( tcp, len, NULL, 1 );