lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:	Fri, 24 Aug 2007 12:40:48 +0400
From:	Alexey Kuznetsov <>
To:	Lennert Buytenhek <>
Cc:	TJ <>,
Subject: Re: Problem with implementation of TCP_DEFER_ACCEPT?


> > At present with TCP_DEFER_ACCEPT the kernel treats the RFC 793 handshake
> > as invalid; dropping the ACK from the client without replying so the
> > client doesn't know the server has in fact set it's internal ACKed flag.
> > 
> > If the client doesn't send a packet containing data before the SYN_ACK
> > time-outs finally expire the connection will be dropped.
> A brought this up a long, long time ago, and I seem to remember
> Alexey Kuznetsov explained me at the time that this was intentional.

Obviously, I said something like "it is exactly what TCP_DEFER_ACCEPT does".

There is no protocol violation here, ACK from client is considered as lost,
it is quite normal and happens all the time. Handshake is not complete,
server remains in SYN-RECV state and continues to retransmit SYN-ACK.
If client tried to cheat and is not going to send its request,
connection will time out.


To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to
More majordomo info at

Powered by blists - more mailing lists