wenquan2015 commented on code in PR #17691:
URL: https://github.com/apache/nuttx/pull/17691#discussion_r2652140612
##########
net/tcp/tcp_input.c:
##########
@@ -744,10 +744,111 @@ static void tcp_input(FAR struct net_driver_s *dev,
uint8_t domain,
conn = tcp_active(dev, tcp);
if (conn)
{
- /* We found an active connection.. Check for the subsequent SYN
+ uint32_t seq;
+ uint32_t rcvseq;
+
+ seq = tcp_getsequence(tcp->seqno);
+ rcvseq = tcp_getsequence(conn->rcvseq);
+
+ /* rfc793 p66:
+ * "If the state is SYN-SENT then
+ * first check the ACK bit
+ * If the ACK bit is set
+ * If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
+ * a reset (unless the RST bit is set, if so drop
+ * the segment and return)"
+ */
+
+ if ((conn->tcpstateflags & TCP_STATE_MASK) == TCP_SYN_SENT)
+ {
+ uint32_t ackseq;
+ if ((tcp->flags & TCP_ACK) != 0)
+ {
+ ackseq = tcp_getsequence(tcp->ackno);
+ if (ackseq != tcp_getsequence(conn->sndseq))
+ {
+ if ((tcp->flags & TCP_RST) != 0)
+ {
+ goto drop;
+ }
+
+ goto reset;
+ }
+
+ /* rfc793 p67: Now ACK is acceptable.
+ * "If the RST bit is set
+ * If the ACK was acceptable then signal the user "error:
+ * connection reset", drop the segment, enter CLOSED state,
+ * delete TCB, and return."
+ */
+
+ if ((tcp->flags & TCP_RST) != 0)
+ {
+ /* fallback to label found rst handle */
+
+ goto found;
+ }
+
+ /* rfc793 p68: "fifth, if neither of the SYN or RST bits is set
+ * then drop the segment and return."
+ */
+
+ if ((tcp->flags & TCP_SYN) == 0)
+ {
+ goto drop;
+ }
+ }
+ else if ((tcp->flags & TCP_RST) != 0 ||
+ (tcp->flags & TCP_SYN) == 0)
+ {
+ /* rfc793 p67: 1) "If a reset was sent, discard the segment
+ * and return" p68 2) "fifth, if neither of the SYN or RST
+ * bits is set then drop the segment and return."
+ */
+
+ goto drop;
+ }
+ }
+
+ /* RFC793, 1) page 37 Reset Processing: "In all states except
+ * SYN-SENT, all reset (RST) segments are validated by checking
+ * their SEQ-fields."
+ * 2) page 69 In all states except SYN-SENT: "If an incoming
+ * segment is not acceptable, an acknowledgment should be sent
+ * in reply (unless the RST bit is set, if so drop the segment
+ * and return)".
+ */
+
+ if ((conn->tcpstateflags & TCP_STATE_MASK) != TCP_SYN_SENT &&
+ ((conn->tcpstateflags & TCP_STATE_MASK) >= TCP_SYN_RCVD &&
+ (conn->tcpstateflags & TCP_STATE_MASK) <= TCP_LAST_ACK))
Review Comment:
base on the tcp state macro define as follow，TCP_SYN_SENT is bigger than
TCP_SYN_RCVD, but the block need to exclude state TCP_SYN_SENT :
```
# define TCP_ALLOCATED 0x01 /* The connection is allocated, but not yet
initialized */
# define TCP_SYN_RCVD 0x02
# define TCP_SYN_SENT 0x03
# define TCP_ESTABLISHED 0x04
# define TCP_FIN_WAIT_1 0x05
# define TCP_FIN_WAIT_2 0x06
# define TCP_CLOSE_WAIT 0x07
# define TCP_CLOSING 0x08
# define TCP_TIME_WAIT 0x09
# define TCP_LAST_ACK 0x0a
```
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