Re: [PATCH v2] ALSA: usb-audio: Fix potential out-of-bound accesses for Extigy devices

[Takashi Iwai <tiwai@xxxxxxx>]

On Tue, 19 Nov 2024 15:28:13 +0100,
Benoît Sevens wrote:
> 
> A bogus devices can provide a bNumConfigurations value that exceeds the
> initial value used in usb_get_configuration for allocating dev->config.
> 
> This can lead to out-of-bounds accesses later, e.g. in
> usb_destroy_configuration.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Cc: stable@xxxxxxxxxx
> Signed-off-by: Benoît Sevens <bsevens@xxxxxxxxxx>
> ---
> v2:
>  - Also add sanity checks to snd_usb_mbox2_boot_quirk and 
>    snd_usb_mbox3_boot_quirk

Thanks for the revised patch.

Although we should fix better in a long term, a duct-tape fix like
this wouldn't hurt.

But one thing I'm considering is...

> @@ -565,8 +566,11 @@ static int snd_usb_extigy_boot_quirk(struct usb_device *dev, struct usb_interfac
>  				      0x10, 0x43, 0x0001, 0x000a, NULL, 0);
>  		if (err < 0)
>  			dev_dbg(&dev->dev, "error sending boot message: %d\n", err);
> +		num_configs = dev->descriptor.bNumConfigurations;
>  		err = usb_get_descriptor(dev, USB_DT_DEVICE, 0,
>  				&dev->descriptor, sizeof(dev->descriptor));
> +		if (dev->descriptor.bNumConfigurations > num_configs)
> +			dev->descriptor.bNumConfigurations = num_configs;

IMO, we can get the new descriptor locally, then do
compare-and-store.  If bNumConfiguration is unexpectedly large, it can
return an error without modifying the original descriptor.


Takashi