[Backport v3.5-branch] net: tcp: Send RST reply for unexpected TCP packets #64321
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Add a helper function which allows to send a RST packet in response to an unexpected TCP packet, w/o associated connection or net context. Signed-off-by: Robert Lubos <[email protected]> (cherry picked from commit a28215d)
Send RST as a reply for unexpected TCP packets in the following scenarios: 1) Unexpected ACK value received during handshake (connection still open on the peer side), 2) Unexpected data packet on a listening port (accepted connection closed), 3) SYN received on a closed port. This allows the other end to detect that the connection is no longer valid (for example due to reboot) and release the resources. Signed-off-by: Robert Lubos <[email protected]> (cherry picked from commit 95d9543)
Add tests which verify that Zephyr's TCP stack replies with RST packet as expected. Signed-off-by: Robert Lubos <[email protected]> (cherry picked from commit 2b601b3)
Add Kconfig option to control TCP RST behavior on connection attempts on unbound ports. If enabled, TCP stack will reply with RST packet (enabled by default). Signed-off-by: Robert Lubos <[email protected]> (cherry picked from commit 4ea3d24)
The test delegates putting the server socket into listening (i. e. calling listen() on the socket) to a separate thread, which did have a chance to run before client attempted to establish TCP connection. This was not visible before, as we did not reply with RST to a connection attempt on a closed port, so the connection was eventually establish after SYN retransmission. But as we do reject such a connection now with RST, the connection attempt failed. Therefore, a small delay was added after spawning the server thread, to give it a chance to configure the server socket. Additionally, lower the CONFIG_NET_TCP_TIME_WAIT_DELAY value so that TCP contexts are released earlier, and add a respective delay in the test teardown function. Not doing so also triggered unneeded SYN retransmissions, as there were no enough TCP context to accept the incoming connection, before freeing the resources allocated for the previous one. Signed-off-by: Robert Lubos <[email protected]> (cherry picked from commit 822a82d)
rlubos
approved these changes
Oct 24, 2023
jukkar
approved these changes
Oct 24, 2023
jhedberg
approved these changes
Oct 24, 2023
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Backport 822a82d~5..822a82d from #64029.
Fixes #63966