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

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Date:	Tue, 02 Dec 2014 13:59:20 +0100
From:	Frank Haverkamp <haver@...ux.vnet.ibm.com>
To:	Ian Abbott <abbotti@....co.uk>
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()

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?

> 
> Signed-off-by: Ian Abbott <abbotti@....co.uk>
> Cc: <stable@...r.kernel.org> # 3.14.x # 3.15.x # 3.16.x # 3.17.x
> ---
>  drivers/misc/genwqe/card_utils.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/misc/genwqe/card_utils.c b/drivers/misc/genwqe/card_utils.c
> index 7cb3b7e..1ca94e6 100644
> --- a/drivers/misc/genwqe/card_utils.c
> +++ b/drivers/misc/genwqe/card_utils.c
> @@ -590,6 +590,8 @@ int genwqe_user_vmap(struct genwqe_dev *cd, struct dma_mapping *m, void *uaddr,
>  				 m->nr_pages,
>  				 1,		/* write by caller */
>  				 m->page_list);	/* ptrs to pages */
> +	if (rc < 0)
> +		goto fail_get_user_pages;
> 
>  	/* assumption: get_user_pages can be killed by signals. */
>  	if (rc < m->nr_pages) {

Regards

Frank

Acked-by: Frank Haverkamp <haver@...ux.vnet.ibm.com>


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