Re: [PATCH v2 2/2] drm/xe/queue: move xa_alloc to prevent UAF

[Matthew Brost <matthew.brost@intel.com>]

On Wed, Sep 25, 2024 at 08:14:28AM +0100, Matthew Auld wrote:
> Evil user can guess the next id of the queue before the ioctl completes
> and then call queue destroy ioctl to trigger UAF since create ioctl is
> still referencing the same queue. Move the xa_alloc all the way to the end
> to prevent this.
> 
> v2:
>  - Rebase
> 
> Fixes: 2149ded63079 ("drm/xe: Fix use after free when client stats are captured")
> Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> Cc: Matthew Brost <matthew.brost@intel.com>

Reviewed-by: Matthew Brost <matthew.brost@intel.com>

> ---
>  drivers/gpu/drm/xe/xe_exec_queue.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_exec_queue.c b/drivers/gpu/drm/xe/xe_exec_queue.c
> index 7743ebdcbf4b..d098d2dd1b2d 100644
> --- a/drivers/gpu/drm/xe/xe_exec_queue.c
> +++ b/drivers/gpu/drm/xe/xe_exec_queue.c
> @@ -635,12 +635,14 @@ int xe_exec_queue_create_ioctl(struct drm_device *dev, void *data,
>  		}
>  	}
>  
> +	q->xef = xe_file_get(xef);
> +
> +	/* user id alloc must always be last in ioctl to prevent UAF */
>  	err = xa_alloc(&xef->exec_queue.xa, &id, q, xa_limit_32b, GFP_KERNEL);
>  	if (err)
>  		goto kill_exec_queue;
>  
>  	args->exec_queue_id = id;
> -	q->xef = xe_file_get(xef);
>  
>  	return 0;
>  
> -- 
> 2.46.1
>