Re: [PATCH] aio: fix io_setup/io_destroy race

[Benjamin LaHaise]

On Wed, Mar 07, 2012 at 05:16:35AM +0000, Al Viro wrote:
> Have ioctx_alloc() return an extra reference, so that caller would drop it
> on success and not bother with re-grabbing it on failure exit.  The current
> code is obviously broken - io_destroy() from another thread that managed
> to guess the address io_setup() would've returned would free ioctx right
> under us; gets especially interesting if aio_context_t * we pass to
> io_setup() points to PROT_READ mapping, so put_user() fails and we end
> up doing io_destroy() on kioctx another thread has just got freed...
> 
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>

Signed-off-by: Benjamin LaHaise <bcrl@xxxxxxxxx>

The fix looks good, and works with a quick test program checking the two cases 
involved (ioctx create success + failure due to PROT_READ).

		-ben
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