Bug 250363

Summary: [tcp] data in syn_ack should be ignored
Product: Base System Reporter: Yong-Hao Zou <yonghaoz1994>
Component: kernAssignee: Michael Tuexen <tuexen>
Status: New ---    
Severity: Affects Some People CC: net, tuexen
Priority: ---    
Version: Unspecified   
Hardware: Any   
OS: Any   

Description Yong-Hao Zou 2020-10-15 09:57:22 UTC
data in syn_ack should be ignored as the following packetdrill script shows:

```
0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
0.000 fcntl(3, F_GETFL) = 0x2 (flags O_RDWR)
0.000 fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK) = 0

// Establish connection and verify that there was no error.
0.100 connect(3, ..., ...) = -1
0.100 > S 0:0(0) <...>

+0.1 < S. 1:513(512) ack 1 win 19712 
// f-stack/FreeBSD ack 513, Linux ack 1
+0.1 > . 1:1(0) ack 1

```