[alsa-devel] [PATCH v3 2/3] ALSA: usb-audio: More strict sanity checks for clock parsers

[Ruslan Bilovol]

Hi Takashi,

On Thu, Apr 5, 2018 at 3:11 PM, Takashi Iwai <tiwai at suse.de> wrote:
> The sanity checks introduced for malformed descriptors loosely check
> the given descriptor size, although the size greater than the defined
> description is invalid.  It was due to a concern of any funky firmware
> in the actual products.  But this doesn't look hitting, and any sane
> products must have the defined descriptors.
>
> So in this patch, we make the validators more strict, allowing only
> with the defined descriptor sizes.
>
> Suggested-by: Ruslan Bilovol <ruslan.bilovol at gmail.com>
> Signed-off-by: Takashi Iwai <tiwai at suse.de>
> ---
>  sound/usb/clock.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/sound/usb/clock.c b/sound/usb/clock.c
> index 27c2275a2505..cbf68ab01836 100644
> --- a/sound/usb/clock.c
> +++ b/sound/usb/clock.c
> @@ -52,7 +52,7 @@ static void *find_uac_clock_desc(struct usb_host_interface *iface, int id,
>  static bool validate_clock_source_v2(void *p, int id)
>  {
>         struct uac_clock_source_descriptor *cs = p;
> -       return cs->bLength >= sizeof(*cs) && cs->bClockID == id;
> +       return cs->bLength == sizeof(*cs) && cs->bClockID == id;
>  }
>
>  static bool validate_clock_source_v3(void *p, int id)
> @@ -65,7 +65,7 @@ static bool validate_clock_selector_v2(void *p, int id)
>  {
>         struct uac_clock_selector_descriptor *cs = p;
>         return cs->bLength >= sizeof(*cs) && cs->bClockID == id &&
> -               cs->bLength >= 5 + cs->bNrInPins;
> +               cs->bLength == 5 + cs->bNrInPins;

This one still has an issue, here we should check it next way:
               cs->bLength == 7 + cs->bNrInPins;

This is because bLength is 7+bNrInPins as per UAC2 spec, not 5 :P

Thanks,
Ruslan

>  }
>
>  static bool validate_clock_selector_v3(void *p, int id)
> @@ -77,7 +77,7 @@ static bool validate_clock_selector_v3(void *p, int id)
>  static bool validate_clock_multiplier_v2(void *p, int id)
>  {
>         struct uac_clock_multiplier_descriptor *cs = p;
> -       return cs->bLength >= sizeof(*cs) && cs->bClockID == id;
> +       return cs->bLength == sizeof(*cs) && cs->bClockID == id;
>  }
>
>  static bool validate_clock_multiplier_v3(void *p, int id)
> --
> 2.16.2
>