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Date:      Wed, 08 Mar 2017 09:44:17 +0000
From:      bugzilla-noreply@freebsd.org
To:        freebsd-bugs@FreeBSD.org
Subject:   [Bug 217637] One TCP connection accepted TWO time
Message-ID:  <bug-217637-8@https.bugs.freebsd.org/bugzilla/>

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D217637

            Bug ID: 217637
           Summary: One TCP connection accepted TWO time
           Product: Base System
           Version: 10.3-STABLE
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs@FreeBSD.org
          Reporter: alexandre.martins@stormshield.eu

Created attachment 180626
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=3D180626&action=
=3Dedit
tcpdump from the client side view

Hello,

I currently having a strange problem, my web server accept two time the SAME
tcp connection.

After digging, it's due to a TCP retransmission. There is the TCP scenario:


Client     |     SERVER     | Comment

SYN ------------->
    <------------- SYN/ACK
ACK ------------->             Connection accepted in the server

PUSH/ACK -------->             POST /someURL HTTP/1.0\r\nContent-length:
10\r\n\r\n

    <------------- PUSH/ACK    500 error
    <------------- FIN/ACK     Connection closed in the server

PUSH/ACK -------->             data of the post
    <------------- RST         This reset seems to be lost or filtered by s=
ome
firewall=20

PUSH/ACK -------->             Re-xmit all: POST /someURL
HTTP/1.0\r\nContent-length: 10\r\n\r\ndatadatada
        ?????????? =3D=3D=3D=3D=3D=3D=3D>    this cause the connection to b=
e RE-ACCEPTED by
the server !?!?!

ACK ------------->             Ack the 500 error message
ACK ------------->             Ack the FIN
    <------------- ACK         This ACK seems BROKEN. The TCP sequence mism=
atch

And the connection never close properly until the TCP timeout.

I attach the tcpdump of this connection from the client side.

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