linux/tools/testing/selftests/net/netfilter/packetdrill/conntrack_syn_challenge_ack.pkt

// Check connection re-use, i.e. peer that receives the SYN answers with
// a challenge-ACK.
// Check that conntrack lets all packets pass, including the challenge ack,
// and that a new connection is established.

`packetdrill/common.sh`

// S  >
//  . < (challnge-ack)
// R. >
// S  >
// S. <
// Expected outcome: established connection.

+0 `$xtables -A INPUT -p tcp -m conntrack --ctstate INVALID -j DROP`
+0 `$xtables -A OUTPUT -p tcp -m conntrack --ctstate INVALID -j DROP`

+0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+0 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0

0.1 connect(3, ..., ...) = -1 EINPROGRESS (Operation now in progress)
0.1 > S 0:0(0) win 65535 <mss 1460,sackOK,TS val 1 ecr 0,nop,wscale 8>

// Challenge ACK, old incarnation.
0.1 < . 145824453:145824453(0) ack 643160523 win 240 <mss 1460,nop,nop,TS val 1 ecr 1,nop,wscale 0>

+0.01 > R 643160523:643160523(0) win 0

+0.01 `conntrack -f $NFCT_IP_VERSION -L -p tcp --dport 8080 2>/dev/null | grep UNREPLIED | grep -q SYN_SENT`

// Must go through.
+0.01 > S 0:0(0) win 65535 <mss 1460,sackOK,TS val 1 ecr 0,nop,wscale 8>

// correct synack
+0.1 < S. 0:0(0) ack 1 win 250 <mss 1460,nop,nop,TS val 1 ecr 1,nop,wscale 0>

// 3whs completes.
+0.01 > . 1:1(0) ack 1 win 256 <nop,nop,TS val 1 ecr 1>

+0 `conntrack -f $NFCT_IP_VERSION -L -p tcp --dport 8080 2>/dev/null | grep ESTABLISHED | grep -q ASSURED`

// No packets should have been marked INVALID
+0 `$xtables -v -S INPUT  | grep INVALID | grep -q -- "-c 0 0"`
+0 `$xtables -v -S OUTPUT | grep INVALID | grep -q -- "-c 0 0"`