buglwIP - A Lightweight TCP/IP stack - Bugs: bug #39565, Server "ddosed" by PCBs...

 
 

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bug #39565: Server "ddosed" by PCBs in LAST_ACK state

Submitter:  Roman Trunov <thestream>
Submitted:  Thu 25 Jul 2013 09:43:18 AM UTC
   
 
Category:  TCP Severity:  3 - Normal
Item Group:  Change Request Status:  Fixed
Privacy:  Public Assigned to:  goldsimon
Open/Closed:  Closed Planned Release:  None
lwIP version:  1.4.1

Wed 18 Feb 2015 08:32:48 PM UTC, comment #1: 

Fixed, thanks for the hint.

Independently of this bug, I've changed the deallocation scheme prefer killing LAST_ACK, but explicitly killing LAST_ACK (and CLOSING) independent of the prio (no data is lost) seems like a better idea.

Simon Goldschmidt <goldsimon>
Group administrator
Thu 25 Jul 2013 09:43:18 AM UTC, original submission:  

Our device is a server which suddenly stopped responding. LWIP on the device was configured for 10 PCBs for incoming connections. We found that all 10 PCBs were active in "LAST_ACK" state, so no more incoming connections could be accepted.

Regardless of the reason caused last ACK to be lost (e.g. improperly configured NAT/firewall on the way), bad thing is that server becomes completely blocked for 120 seconds (default TCP_MSL * 2) until one of PCBs expires.

Although I could make some kind of workaround by reducing TCP_MSL to e.g. 5 seconds, I suggest to implement more aggressive strategy for PCB allocation - reuse LAST_ACK PCBs in the similar way like we already handling TIME_WAIT pcbs.

Roman Trunov <thestream>

 

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    Follow 3 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2015-02-18 goldsimon StatusNone Fixed
        Assigned toNone goldsimon
        Open/ClosedOpen Closed

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