Re: [PATCH] misc: genwqe: check for error from get_user_pages_fast()

[Ian Abbott <abbotti@mev.co.uk>]

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@mev.co.uk> )=-
-=(                          Web: http://www.mev.co.uk/  )=-