[36457] in bugtraq
Re: Linux 2.4.27 SECURITY BUG - TCP Local (probable Remote) Denial
daemon@ATHENA.MIT.EDU (David S. Miller)
Mon Sep 13 20:27:36 2004
Date: Sat, 11 Sep 2004 20:47:10 -0700
From: "David S. Miller" <davem@davemloft.net>
To: "Wolfpaw - Dale Corse" <admin@wolfpaw.net>
Cc: linux-kernel@vger.kernel.org, grsecurity@grsecurity.net,
bugtraq@securityfocus.com
Message-Id: <20040911204710.4aa7abed.davem@davemloft.net>
In-Reply-To: <000001c49872$99333460$0200a8c0@wolf>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
On Sat, 11 Sep 2004 20:45:43 -0600
"Wolfpaw - Dale Corse" <admin@wolfpaw.net> wrote:
> As for it being an application bug - it may be one in Mysql not
> closing the sockets, but it is a Kernel Bug that allows CLOSE_WAIT
> sockets to clog up the connection queues, and cause a DOS conditions
> on other applications (such as Apache). Since most software used for
> denial of service is badly written (intentionally) to exploit the
> holes, the error should be fixed, not blamed on faulty software.
If the application doesn't close it's file descriptors there is
absolutely nothing the kernel can do about it.
It's a resource leak, plain and simple.
> That being said - below is a the proper description, and the code
> used to exploit it. Hope it helps. This version is not the one
> which invokes the CLOSE_WAIT state, but rather the TIME_WAIT one,
> I am not able to publish the source code for the CLOSE_WAIT bug.
There is nothing wrong with creating tons of TIME_WAIT sockets,
they simply time out after 60 seconds (unless hit by a RESET
packet or similar). This is how TCP works.
> The log however clearly shows that a mysql descriptor is closed,
> and then used immediately again by the socket call, which causes it
> never to end up getting closed. Linux apparently has either no
> timeout for CLOSE_WAIT, or it's a very very long one.. Either way
> is a bad thing.
Please do us all a favor and learn how TCP works.
CLOSE_WAIT means simply that only one side of the TCP
connection has done a close. Therefore the other end
stays open until that side closes as well.
There is no way to "time things out" or release the
state.
