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

[Andrew Morton <akpm@osdl.org>]

On Wed, 17 Jan 2007 10:55:54 +0100
Sébastien Dugué <sebastien.dugue@bull.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.