Re: [PATCH v3] zram: fix possible use after free in zcomp_create()

[Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>]

On (09/08/15 10:39), Luis Henriques wrote:
> zcomp_create() verifies the success of zcomp_strm_{multi,siggle}_create()
> through comp->stream, which can potentially be pointing to memory that was
> freed if these functions returned an error.
> 
> While at it, replace a 'ERR_PTR(-ENOMEM)' by a more generic
> 'ERR_PTR(error)' as in the future zcomp_strm_{multi,siggle}_create() could
> return other error codes.  Function documentation updated accordingly.
> 
> Fixes: beca3ec71fe5 ("zram: add multi stream functionality")
> Cc: stable@vger.kernel.org
> Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
> Cc: Minchan Kim <minchan@kernel.org>
> Signed-off-by: Luis Henriques <luis.henriques@canonical.com>


Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>

	-ss

> ---
> 
> Changes since v2:
>  * Renamed local variable 'ret' to 'error'
>  * Usage of 'ERR_PTR(error)' to accommodate future error codes returned by
>    zcomp_strm_{multi,siggle}_create
>  (all suggested by Minchan)
> 
> Changes since v1:
>  * Check zcomp_strm_{multi,siggle}_create() return code instead
>    comp->stream (suggested by Sergey)
> 
> drivers/block/zram/zcomp.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
> index 965d1afb0eaa..5cb13ca3a3ac 100644
> --- a/drivers/block/zram/zcomp.c
> +++ b/drivers/block/zram/zcomp.c
> @@ -330,12 +330,14 @@ void zcomp_destroy(struct zcomp *comp)
>   * allocate new zcomp and initialize it. return compressing
>   * backend pointer or ERR_PTR if things went bad. ERR_PTR(-EINVAL)
>   * if requested algorithm is not supported, ERR_PTR(-ENOMEM) in
> - * case of allocation error.
> + * case of allocation error, or any other error potentially
> + * returned by functions zcomp_strm_{multi,single}_create.
>   */
>  struct zcomp *zcomp_create(const char *compress, int max_strm)
>  {
>  	struct zcomp *comp;
>  	struct zcomp_backend *backend;
> +	int error;
>  
>  	backend = find_backend(compress);
>  	if (!backend)
> @@ -347,12 +349,12 @@ struct zcomp *zcomp_create(const char *compress, int max_strm)
>  
>  	comp->backend = backend;
>  	if (max_strm > 1)
> -		zcomp_strm_multi_create(comp, max_strm);
> +		error = zcomp_strm_multi_create(comp, max_strm);
>  	else
> -		zcomp_strm_single_create(comp);
> -	if (!comp->stream) {
> +		error = zcomp_strm_single_create(comp);
> +	if (error) {
>  		kfree(comp);
> -		return ERR_PTR(-ENOMEM);
> +		return ERR_PTR(error);
>  	}
>  	return comp;
>  }
>