Re: [PATCH] drm/nouveau: Fix a potential theorical leak in nouveau_get_backlight_name()

[Lyude Paul]

Sorry I totally missed this patch up until now, noticed it while going through
unread emails today. This is:

Reviewed-by: Lyude Paul <lyude@xxxxxxxxxx>

FWIW, if there's something you need reviews on that hasn't gotten looked at
after a few weeks feel free to poke the nouveau list/me.

Anyway, I will go ahead and push this to drm-misc-fixes in a moment. Thanks!

On Wed, 2022-02-09 at 07:03 +0100, Christophe JAILLET wrote:
> If successful ida_simple_get() calls are not undone when needed, some
> additional memory may be allocated and wasted.
> 
> Here, an ID between 0 and MAX_INT is required. If this ID is >=100, it is
> not taken into account and is wasted. It should be released.
> 
> Instead of calling ida_simple_remove(), take advantage of the 'max'
> parameter to require the ID not to be too big. Should it be too big, it
> is not allocated and don't need to be freed.
> 
> While at it, use ida_alloc_xxx()/ida_free() instead to
> ida_simple_get()/ida_simple_remove().
> The latter is deprecated and more verbose.
> 
> Fixes: db1a0ae21461 ("drm/nouveau/bl: Assign different names to interfaces")
> Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
> ---
> This patch is more a clean-up than a fix.
> It is unlikely than >= 100 backlight devices will be registered, and the
> over allocation would occur even much later when the underlying xarray is
> full.
> 
> I also think that the 'if (bl->id >= 0)' before the ida_simple_remove()
> calls are useless. We don't store the id if a negative (i.e. error) is
> returned by ida_simple_get().
> 
> Finally, having a '#define BL_MAX_MINORS 99' could be better than a
> magic number in the code.
> ---
>  drivers/gpu/drm/nouveau/nouveau_backlight.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/nouveau/nouveau_backlight.c
> b/drivers/gpu/drm/nouveau/nouveau_backlight.c
> index ae2f2abc8f5a..ccd080ba30bf 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_backlight.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_backlight.c
> @@ -46,8 +46,8 @@ static bool
>  nouveau_get_backlight_name(char backlight_name[BL_NAME_SIZE],
>                            struct nouveau_backlight *bl)
>  {
> -       const int nb = ida_simple_get(&bl_ida, 0, 0, GFP_KERNEL);
> -       if (nb < 0 || nb >= 100)
> +       const int nb = ida_alloc_max(&bl_ida, 99, GFP_KERNEL);
> +       if (nb < 0)
>                 return false;
>         if (nb > 0)
>                 snprintf(backlight_name, BL_NAME_SIZE, "nv_backlight%d",
> nb);
> @@ -414,7 +414,7 @@ nouveau_backlight_init(struct drm_connector *connector)
>                                             nv_encoder, ops, &props);
>         if (IS_ERR(bl->dev)) {
>                 if (bl->id >= 0)
> -                       ida_simple_remove(&bl_ida, bl->id);
> +                       ida_free(&bl_ida, bl->id);
>                 ret = PTR_ERR(bl->dev);
>                 goto fail_alloc;
>         }
> @@ -442,7 +442,7 @@ nouveau_backlight_fini(struct drm_connector *connector)
>                 return;
>  
>         if (bl->id >= 0)
> -               ida_simple_remove(&bl_ida, bl->id);
> +               ida_free(&bl_ida, bl->id);
>  
>         backlight_device_unregister(bl->dev);
>         nv_conn->backlight = NULL;

-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat