linux-kernel - Re: [PATCH] misc: genwqe: check for error from get_user_pages

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Message-ID: <547DBEC2.5010505@mev.co.uk>
Date:	Tue, 02 Dec 2014 13:29:38 +0000
From:	Ian Abbott <abbotti@....co.uk>
To:	haver@...ux.vnet.ibm.com
CC:	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	Thadeu Lima De Souza Cascardo <thadeul@...ibm.com>
Subject: Re: [PATCH] misc: genwqe: check for error from get_user_pages_fast()

On 02/12/14 12:59, Frank Haverkamp wrote:
> Hi Ian,
>
> thanks for reviewing our code and sorry for not answering immediately.
>
> Am Donnerstag, den 06.11.2014, 16:23 +0000 schrieb Ian Abbott:
>> `genwqe_user_vmap()` calls `get_user_pages_fast()` and if the return
>> value is less than the number of pages requested, it frees the pages and
>> returns an error (`-EFAULT`).  However, it fails to consider a negative
>> error return value from `get_user_pages_fast()`.  In that case, the test
>> `if (rc < m->nr_pages)` will be false (due to promotion of `rc` to a
>> large `unsigned int`) and the code will continue on to call
>> `genwqe_map_pages()` with an invalid list of page pointers.  Fix it by
>> bailing out if `get_user_pages_fast()` returns a negative error value.
>
> True. Did you find this by manual inspection of the code or did you use
> tools to figure it out?

I just spotted it while grepping for examples of drivers that used 
get_user_pages() or get_user_pages_fast() as I want to use it in a 
driver for some custom hardware.

-- 
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti@....co.uk> )=-
-=(                          Web: http://www.mev.co.uk/  )=-
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