1 // SPDX-License-Identifier: GPL-2.0
2 // Test what happens when client does not provide MD5 on SYN,
3 // but then does on the ACK that completes the three-way handshake.
4 
5 `./defaults.sh`
6 
7 // Establish a connection.
8     0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
9    +0 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
10    +0 bind(3, ..., ...) = 0
11    +0 listen(3, 1) = 0
12 
13    +0 < S 0:0(0) win 32792 <mss 1000,sackOK,nop,nop,nop,wscale 10>
14    +0 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK,nop,wscale 8>
15 // Ooh, weird: client provides MD5 option on the ACK:
16  +.01 < . 1:1(0) ack 1 win 514 <md5 000102030405060708090a0b0c0d0e0f,nop,nop>
17  +.01 < . 1:1(0) ack 1 win 514 <md5 000102030405060708090a0b0c0d0e0f,nop,nop>
18 
19 // The TCP listener refcount should be 2, but on buggy kernels it can be 0:
20    +0 `grep " 0A " /proc/net/tcp /proc/net/tcp6 | grep ":1F90"`
21 
22 // Now here comes the legit ACK:
23  +.01 < . 1:1(0) ack 1 win 514
24 
25 // Make sure the connection is OK:
26    +0 accept(3, ..., ...) = 4
27 
28  +.01 write(4, ..., 1000) = 1000
29