[Bug 217637] One TCP connection accepted TWO time

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=217637

            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 at FreeBSD.org
          Reporter: alexandre.martins at stormshield.eu

Created attachment 180626
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=180626&action=edit
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 some
firewall 

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

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

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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