selftests/net: Add TCP-AO RST test

Check that both active and passive reset works and correctly sign
segments with TCP-AO or don't send RSTs if not possible to sign.
A listening socket with backlog = 0 gets one connection in accept
queue, another in syn queue. Once the server/listener socket is
forcibly closed, client sockets aren't connected to anything.
In regular situation they would receive RST on any segment, but
with TCP-AO as there's no listener, no AO-key and unknown ISNs,
no RST should be sent.

And "passive" reset, where RST is sent on reply for some segment
(tcp_v{4,6}_send_reset()) - there use TCP_REPAIR to corrupt SEQ numbers,
which later results in TCP-AO signed RST, which will be verified and
client socket will get EPIPE.

No TCPAORequired/TCPAOBad segments are expected during these tests.

Sample of the output:
> # ./rst_ipv4
> 1..15
> # 1462[lib/setup.c:254] rand seed 1686611171
> TAP version 13
> ok 1 servered 1000 bytes
> ok 2 Verified established tcp connection
> ok 3 sk[0] = 7, connection was reset
> ok 4 sk[1] = 8, connection was reset
> ok 5 sk[2] = 9
> ok 6 MKT counters are good on server
> ok 7 Verified established tcp connection
> ok 8 client connection broken post-seq-adjust
> ok 9 client connection was reset
> ok 10 No segments without AO sign (server)
> ok 11 Signed AO segments (server): 0 => 30
> ok 12 No segments with bad AO sign (server)
> ok 13 No segments without AO sign (client)
> ok 14 Signed AO segments (client): 0 => 30
> ok 15 No segments with bad AO sign (client)
> # Totals: pass:15 fail:0 xfail:0 xpass:0 skip:0 error:0
Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/net/tcp_ao/Makefile

@@ -4,6 +4,7 @@ TEST_BOTH_AF += connect
 TEST_BOTH_AF += connect-deny
 TEST_BOTH_AF += icmps-accept icmps-discard
 TEST_BOTH_AF += restore
+TEST_BOTH_AF += rst
 TEST_BOTH_AF += seq-ext
 TEST_BOTH_AF += setsockopt-closed
 TEST_BOTH_AF += unsigned-md5

tools/testing/selftests/net/tcp_ao/lib/sock.c

@@ -566,7 +566,7 @@ ssize_t test_client_loop(int sk, char *buf, size_t buf_sz,
 
 			got = recv(sk, msg + bytes, sizeof(msg) - bytes, 0);
 			if (got <= 0)
-				test_error("recv(): %zd", got);
+				return i;
 			bytes += got;
 		} while (bytes < sent);
 		if (bytes > sent)