Bug 250360 - [tcp] connections should be closed if a same packet without FIN is received after FIN received
Summary: [tcp] connections should be closed if a same packet without FIN is received a...
Status: Closed Works As Intended
Alias: None
Product: Base System
Classification: Unclassified
Component: kern (show other bugs)
Version: Unspecified
Hardware: Any Any
: --- Affects Some People
Assignee: Michael Tuexen
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2020-10-15 08:15 UTC by Yonghao Zou
Modified: 2021-02-20 21:26 UTC (History)
2 users (show)

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Description Yonghao Zou 2020-10-15 08:15:45 UTC 
The connection should be closed with the following packetdrill script

``
// Establish a connection.
0   socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
+0  setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0

+0  bind(3, ..., ...) = 0
+0  listen(3, 1) = 0

+0  < S 0:0(0) win 32792 <mss 1000,sackOK,nop,nop,nop,wscale 7>
+0 ~ +1  > S. 0:0(0) ack 1 <...>

+.1 < . 1:1(0) ack 1 win 32792
+0  accept(3, ..., ...) = 4
+0 fcntl(4, F_SETFL, O_RDWR|O_NONBLOCK) = 0

+0 < . 1:3962(3961) ack 1 win 28535
+0 < F. 3962:6683(2721) ack 1 win 45489

+0.1 read(4, ..., 177) =  177
+0.1 write(4, ..., 177) =  177
+0.1 write(4, ..., 113) =  113
+0 < . 3962:7468(3506) ack 1 win 29046
+0.1 write(4, ..., 113) =  -1 // current we got 113

```
Comment 1 Michael Tuexen freebsd_committer freebsd_triage 2021-02-20 21:26:11 UTC 
According to RFC 793, page 75, the segment text is ignored in the CLOSE-WAIT state.
No state change should happen, the missing FIN bit is ignored.

The following packetdrill script shows the behaviour, which is in tune with RFC 793:

 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
+0.000 connect(3, ..., ...) = -1 EINPROGRESS (Operation now in progress)
+0.000 > S    0:0(0)               win 65535 <mss 1460,nop,wscale 6,sackOK,TS val 100 ecr 0>
+0.050 < S.   0:0(0)       ack   1 win 65535 <mss 1460,sackOK,eol,eol>
+0.000 >  .   1:1(0)       ack   1 win 65535
+0.050 < F.   1:513(512)   ack   1 win 65535
+0.000 >  .   1:1(0)       ack 514 win 65188
+0.000 recv(3, ..., 256, 0) = 256
+0.050 <  .   1:1025(1024) ack   1 win 65535
+0.000 >  .   1:1(0)       ack 514 win 65444 <nop,nop,sack 1:514>
+0.000 recv(3, ..., 1024, 0) = 256
+0.000 send(3, ..., 512, 0) = 512
+0.000 > P.   1:513(512)   ack 514 win 65535
+0.000 <  . 514:514(0)     ack 513 win 65535
+0.000 close(3) = 0
+0.000 > F. 513:513(0)     ack 514 win 65535
+0.000 <  . 514:514(0)     ack 514 win 65535