Re: usb/core: slab-out-of-bounds in usb_set_configuration

[Andrey Konovalov]

On Mon, Sep 18, 2017 at 8:50 PM, Greg Kroah-Hartman
<gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> On Mon, Sep 18, 2017 at 07:22:24PM +0200, Andrey Konovalov wrote:
>> Hi!
>>
>> I've got the following crash while fuzzing the kernel with syzkaller.
>>
>> On commit ebb2c2437d8008d46796902ff390653822af6cc4 (Sep 18).
>>
>> It seems there's no proper size check of a
>> USB_DT_INTERFACE_ASSOCIATION descriptor. It's only checked that the
>> size is >= 2 in usb_parse_configuration(), so find_iad() might do
>> out-of-bounds access to intf_assoc->bInterfaceCount.
>
> Ah, nice catch!
>
> Does the patch below fix this?

Hi Greg,

I believe it does and the bug is no longer triggered with the
reproducer that I have.

Tested-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>

Thanks!

>
> thanks,
>
> greg k-h
>
> ---------------
>
> diff --git a/drivers/usb/core/config.c b/drivers/usb/core/config.c
> index 4be52c602e9b..a3dbac1938ec 100644
> --- a/drivers/usb/core/config.c
> +++ b/drivers/usb/core/config.c
> @@ -643,15 +643,23 @@ static int usb_parse_configuration(struct usb_device *dev, int cfgidx,
>
>                 } else if (header->bDescriptorType ==
>                                 USB_DT_INTERFACE_ASSOCIATION) {
> +                       struct usb_interface_assoc_descriptor *d;
> +
> +                       d = (struct usb_interface_assoc_descriptor *)header;
> +                       if (d->bLength < USB_DT_INTERFACE_ASSOCIATION_SIZE) {
> +                               dev_warn(ddev,
> +                                        "config %d has an invalid interface association descriptor of length %d, skipping\n",
> +                                        cfgno, d->bLength);
> +                               continue;
> +                       }
> +
>                         if (iad_num == USB_MAXIADS) {
>                                 dev_warn(ddev, "found more Interface "
>                                                "Association Descriptors "
>                                                "than allocated for in "
>                                                "configuration %d\n", cfgno);
>                         } else {
> -                               config->intf_assoc[iad_num] =
> -                                       (struct usb_interface_assoc_descriptor
> -                                       *)header;
> +                               config->intf_assoc[iad_num] = d;
>                                 iad_num++;
>                         }
>
> diff --git a/include/uapi/linux/usb/ch9.h b/include/uapi/linux/usb/ch9.h
> index ce1169af39d7..2a5d63040a0b 100644
> --- a/include/uapi/linux/usb/ch9.h
> +++ b/include/uapi/linux/usb/ch9.h
> @@ -780,6 +780,7 @@ struct usb_interface_assoc_descriptor {
>         __u8  iFunction;
>  } __attribute__ ((packed));
>
> +#define USB_DT_INTERFACE_ASSOCIATION_SIZE      8
>
>  /*-------------------------------------------------------------------------*/
>
>
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