netdev - Re: socket leaks observed in Linux kernel's passive close path

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Message-ID: <Y0genWOLGfy2kQ/M@lunn.ch>
Date:   Thu, 13 Oct 2022 16:20:13 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     "Arankal, Nagaraj" <nagaraj.p.arankal@....com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: socket leaks observed in Linux kernel's passive close path

On Thu, Oct 13, 2022 at 06:47:56AM +0000, Arankal, Nagaraj wrote:
> Description:
> We have observed a strange race condition , where sockets are not freed in kernel in the following condition.
> We have a kernel module , which monitors the TCP connection state changes , as part of the functionality it replaces the default sk_destruct function of all TCP sockets with our module specific routine.  Looks like sk_destruct() is not invoked in following condition and hence the sockets are leaked despite receiving RESET from the remote.
> 
> 1.	Establish a TCP connection between Host A and Host B.
> 2.	Make the client at B to initiate the CLOSE() immediately after 3-way handshake.
> 3.	Server end sends huge amount of data to client and does close on FD.
> 4.	FIN from the client is not ACKED, and server is busy sending the data.
> 5.	RESET is received from the remote client.
> 6.	Sk_destruct() is not invoked due to non-null sk_refcnt or sk_wmem_alloc count.
> 
> Kernel version: Debian Linux 4.19.y(238,247)

Is this reproducible with a modern kernel? v6.0? If this is already
fixed, we need to identify what change fixed it, and get it back
ported. If it is broken in v6.0, and net-next, it first needs fixing
in net-next, and then back porting to the different LTS kernels.

   Andrew