Date: Mon, 12 May 2003 11:57:58 -0700 (PDT)
Message-Id: <20030512.115758.39166911.davem@redhat.com>
To: chas@cmf.nrl.navy.mil
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH][ATM] make clip modular
From: "David S. Miller" <davem@redhat.com>
In-Reply-To: <200305121933.h4CJXM511323@relax.cmf.nrl.navy.mil>
References: <200305121933.h4CJXM511323@relax.cmf.nrl.navy.mil>
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   From: chas williams <chas@cmf.nrl.navy.mil>
   Date: Mon, 12 May 2003 15:33:22 -0400

   this patch lets one build clip as a module.
   
This doesn't work and is quite racey.

   +			if (!atm_clip_ops || !try_module_get(atm_clip_ops->owner)) {

Q: What prevents atm_clip_ops from going NULL between the
   !atm_clip_ops test and the atm_clip_ops->owner dereference?

A: Nothing.

Therefore you have to protect these things some how, I would
suggest using a semaphore, put it right next to atm_clip_ops
and hold it around register, derferegister, and code sequence
like this one trying to get a reference to it.

The various ioctl hooks in net/socket.c are good models to
work from.

MPOA/LEC/MPC probably have nearly identical bugs and it would
be great if you could fix them up too.
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