buglwIP - A Lightweight TCP/IP stack - Bugs: bug #48563, TCP: simultaneous open not...

 
 

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bug #48563: TCP: simultaneous open not supported

Submitter:  Joel Cunningham <jcunningham>
Submitted:  Tue 19 Jul 2016 07:08:48 PM UTC
   
 
Category:  TCP Severity:  3 - Normal
Item Group:  Faulty Behaviour Status:  Duplicate
Privacy:  Public Assigned to:  goldsimon
Open/Closed:  Closed Planned Release:  None
lwIP version:  git head

Tue 19 Jul 2016 08:22:17 PM UTC, comment #2: 

Thanks for the follow up.  I agree I can't think of a real-world use case either

Joel Cunningham <jcunningham>
Group Member
Tue 19 Jul 2016 07:22:15 PM UTC, comment #1: 

Actually, this is a duplicate to bug #35845 (please continue there if there's anything to add). That one was closed as simultaneous open is theroetically possible, but given the fact that most (if not all) protocols have client & server roles, there's no real use for simultaneous open.

Of course, if there's a real requirement, I'm still open to support this, but until now, there wasn't.

Simon Goldschmidt <goldsimon>
Group administrator
Tue 19 Jul 2016 07:08:48 PM UTC, original submission:  

During static analysis of the code referenced in patch #9039, I've noticed that LwIP's TCP implementation doesn't seem to handle simultaneous opens.

A simultaneous open is when two hosts perform an active open at the same time, going from SYN-SENT to SYN-RCVD by receiving only a SYN packet (no ACK flag is set). This results in a single TCP connection between the two hosts

This is described in RFC 793, page 32: https://tools.ietf.org/html/rfc793#page-32.

RFC 1122 (page 87) https://tools.ietf.org/html/rfc1122#page-87, further clarifies simultaneous opens as a MUST and addresses errata from 793

In our handling of SYN-SENT (in tcp_process) we only check for both SYN and ACK flags, not making it possible to only receive a SYN

Joel Cunningham <jcunningham>
Group Member

 

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    Follow 3 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2016-07-19 goldsimon StatusNone Duplicate
        Assigned toNone goldsimon
        Open/ClosedOpen Closed

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