linux-kernel - Re: [PATCH -mm 5/5][AIO] - Add listio syscall support

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Message-Id: <20070123220433.018b40b6.akpm@osdl.org>
Date:	Tue, 23 Jan 2007 22:04:33 -0800
From:	Andrew Morton <akpm@...l.org>
To:	Sébastien Dugué <sebastien.dugue@...l.net>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-aio <linux-aio@...ck.org>,
	Bharata B Rao <bharata@...ibm.com>,
	Christoph Hellwig <hch@...radead.org>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Ulrich Drepper <drepper@...hat.com>,
	Zach Brown <zach.brown@...cle.com>,
	Jean Pierre Dion <jean-pierre.dion@...l.net>,
	Badari Pulavarty <pbadari@...ibm.com>
Subject: Re: [PATCH -mm 5/5][AIO] - Add listio syscall support

On Wed, 17 Jan 2007 10:55:54 +0100
Sébastien Dugué <sebastien.dugue@...l.net> wrote:

> +void lio_check(struct lio_event *lio)
> +{
> +	int ret;
> +
> +	ret = atomic_dec_and_test(&lio->lio_users);
> +
> +	if (unlikely(ret) && lio->lio_notify.notify != SIGEV_NONE) {
> +		/* last one -> notify process */
> +		if (aio_send_signal(&lio->lio_notify))
> +			sigqueue_free(lio->lio_notify.sigq);
> +		kfree(lio);
> +	}
> +}

That's a scary function.  It may (or may not) free the memory at lio,
returning no indication to the caller whether or not that memory is still
allocated.  This is most peculiar - are you really sure there's no
potential for a use-after-free here?

The function is poorly named: I'd expect something called "foo_check" to
not have any side-effects.  This one has gross side-effects.  Want to think
up a better name, please?

And given that this function has global scope, perhaps a little explanatory
comment is in order?

> +struct lio_event *lio_create(struct sigevent __user *user_event,
> +			int mode)

Here too.
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