Re: [PATCH] usb: ljca: bound bank_num in ljca_enumerate_gpio()

[Sakari Ailus]

Hi Maoyi,

Thanks for the patch.

On Thu, Jun 18, 2026 at 02:19:48PM +0800, Maoyi Xie wrote:
> ljca_enumerate_gpio() reads desc->bank_num from the device and loops
> valid_pin[i] = get_unaligned_le32(...) for i < bank_num. valid_pin[]
> holds only LJCA_MAX_GPIO_NUM / 32 = 2 entries.
> 
> Two checks run before the loop. The reply length must match
> struct_size(desc, bank_desc, bank_num). The product
> pins_per_bank * bank_num must not exceed LJCA_MAX_GPIO_NUM. Neither one
> bounds bank_num against the size of valid_pin[]. The reply is capped at
> LJCA_MAX_PAYLOAD_SIZE (60) bytes, so the struct_size check limits
> bank_num to 9. A device that reports bank_num 9 with pins_per_bank 7
> still passes both checks. gpio_num is 63 and the reply is 56 bytes. The
> loop then writes nine u32 into the two entry array and overruns
> valid_pin[] on the stack.
> 
> A broken or malicious LJCA device can therefore overflow the stack.
> Reject a bank_num that does not fit valid_pin[].
> 
> Fixes: acd6199f195d ("usb: Add support for Intel LJCA device")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Maoyi Xie <maoyixie.tju@xxxxxxxxx>
> ---
>  drivers/usb/misc/usb-ljca.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/usb/misc/usb-ljca.c b/drivers/usb/misc/usb-ljca.c
> index c60121faa3da..a1876c05b7c2 100644
> --- a/drivers/usb/misc/usb-ljca.c
> +++ b/drivers/usb/misc/usb-ljca.c
> @@ -596,6 +596,9 @@ static int ljca_enumerate_gpio(struct ljca_adapter *adap)
>  	if (gpio_num > LJCA_MAX_GPIO_NUM)
>  		return -EINVAL;
>  
> +	if (desc->bank_num > ARRAY_SIZE(valid_pin))
> +		return -EINVAL;
> +

This certainly does fix the problem but it looks like the code somehow
appears to assume desc->pins_per_bank is always 32. I guess that's ok as
it's been working in the past.

Acked-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>

>  	/* construct platform data */
>  	gpio_info = kzalloc_obj(*gpio_info);
>  	if (!gpio_info)

-- 
Kind regards,

Sakari Ailus