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tcp: always responds to keep-alive segments

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* It doesn't make sense to have this conditional on our own
  SO_KEEPALIVE support. (CONFIG_NET_TCP_KEEPALIVE)
  Actually we don't have a control on the peer tcp stack,
  who decides to send us keep-alive probes.

* We should respond them for non ESTABLISHED states. eg. FIN_WAIT_2
  See also:
  https://github.com/apache/incubator-nuttx/pull/3919#issuecomment-868248576
This commit is contained in:
YAMAMOTO Takashi
2021-06-29 15:02:47 +09:00
committed by Masayuki Ishikawa
parent 4878b7729c
commit 98e7c6924d
1 changed files with 2 additions and 38 deletions
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net/tcp/tcp_input.c
+2 -38
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@@ -516,42 +516,6 @@ found:
dev->d_len -= (len + iplen); dev->d_len -= (len + iplen);
#ifdef CONFIG_NET_TCP_KEEPALIVE
/* Check for a to KeepAlive probes. These packets have these properties:
*
* - TCP_ACK flag is set. SYN/FIN/RST never appear in a Keepalive probe.
* - Sequence number is the sequence number of previously ACKed data,
* i.e., the expected sequence number minus one.
* - The data payload is one or two bytes.
*
* We would expect a KeepAlive only in the ESTABLISHED state and only after
* some time has elapsed with no network activity. If there is un-ACKed
* data, then we will let the normal TCP re-transmission logic handle that
* case.
*/
if ((tcp->flags & TCP_ACK) != 0 &&
(tcp->flags & (TCP_SYN | TCP_FIN | TCP_RST)) == 0 &&
(conn->tcpstateflags & TCP_STATE_MASK) == TCP_ESTABLISHED &&
(dev->d_len == 0 || dev->d_len == 1) &&
conn->tx_unacked <= 0)
{
uint32_t seq;
uint32_t rcvseq;
seq = tcp_getsequence(tcp->seqno);
rcvseq = tcp_getsequence(conn->rcvseq);
if (TCP_SEQ_LT(seq, rcvseq))
{
/* Send a "normal" acknowledgment of the KeepAlive probe */
tcp_send(dev, conn, TCP_ACK, tcpiplen);
return;
}
}
#endif
/* Check if the sequence number of the incoming packet is what we are /* Check if the sequence number of the incoming packet is what we are
* expecting next. If not, we send out an ACK with the correct numbers * expecting next. If not, we send out an ACK with the correct numbers
* in, unless we are in the SYN_RCVD state and receive a SYN, in which * in, unless we are in the SYN_RCVD state and receive a SYN, in which
@@ -569,8 +533,7 @@ found:
seq = tcp_getsequence(tcp->seqno); seq = tcp_getsequence(tcp->seqno);
rcvseq = tcp_getsequence(conn->rcvseq); rcvseq = tcp_getsequence(conn->rcvseq);
if ((dev->d_len > 0 || ((tcp->flags & (TCP_SYN | TCP_FIN)) != 0)) && if (seq != rcvseq)
seq != rcvseq)
{ {
/* Trim the head of the segment */ /* Trim the head of the segment */
@@ -582,6 +545,7 @@ found:
{ {
/* The segment was completely out of the window. /* The segment was completely out of the window.
* E.g. a retransmit which was not necessary. * E.g. a retransmit which was not necessary.
* E.g. a keep-alive segment.
*/ */
tcp_send(dev, conn, TCP_ACK, tcpiplen); tcp_send(dev, conn, TCP_ACK, tcpiplen);