Re: [PATCH v2] HID: wacom: validate report length in wacom_intuos_pro2_bt_irq

Ping, Jason, could you please Ack this one? Looks good to me, but I always 
prefer to have an Ack from one of you on the Wacom HID driver.

Thanks,

-- 
Jiri Kosina
SUSE Labs

On Mon, 13 Jul 2026, Ibrahim Hashimov wrote:

> wacom_intuos_pro2_bt_irq() receives the wire report length in `len`
> but never consults it before parsing. After the report-id gate it
> unconditionally calls wacom_intuos_pro2_bt_pen() and then, selected by
> features.type, a fixed chain of sub-parsers, none of which receive
> `len`:
> 
> 	wacom_intuos_pro2_bt_pen(wacom);
> 	if (type == INTUOSP2_BT || type == INTUOSP2S_BT) {
> 		wacom_intuos_pro2_bt_touch(wacom);
> 		wacom_intuos_pro2_bt_pad(wacom);
> 		wacom_intuos_pro2_bt_battery(wacom);
> 	} else {
> 		wacom_intuos_gen3_bt_pad(wacom);
> 		wacom_intuos_gen3_bt_battery(wacom);
> 	}
> 
> Each sub-parser dereferences wacom->data at fixed offsets. The furthest
> byte touched on each branch is:
> 
>   INTUOSP2_BT / INTUOSP2S_BT: wacom_intuos_pro2_bt_pad() reads data[285]
> 	(the touchring byte), so the report must be at least 286 bytes;
>   INTUOSHT3_BT ("gen3"): wacom_intuos_gen3_bt_battery() reads data[45],
> 	so the report must be at least 46 bytes.
> 
> features.type is selected from the VID/PID id_table entry and
> wacom_setup_device_quirks() force-registers the pen/pad/touch inputs
> for that type independent of the report descriptor, so a malicious or
> malfunctioning paired/spoofed Bluetooth peripheral can advertise that
> VID/PID and send an undersized report that still satisfies the
> data[0] == 0x80/0x81 gate. The driver then reads past the received
> report and forwards the bytes to userspace via evdev (MSC_SERIAL /
> ABS_MISC / ABS_WHEEL on the pen and pad input nodes), an out-of-bounds
> read with a concrete userspace read-back channel, and a true
> out-of-bounds read on transports whose backing buffer is sized to the
> (small) report descriptor rather than a fixed-size staging buffer.
> 
> This is the same class of bug commit 2f1763f62909 ("HID: wacom: fix
> out-of-bounds read in wacom_intuos_bt_irq") already hardened in the
> sibling wacom_intuos_bt_irq(), which guards each report id against its
> minimum length before parsing.
> 
> Guard wacom_intuos_pro2_bt_irq() the same way: before parsing, reject
> reports shorter than the furthest offset the selected branch actually
> dereferences, warn, and bail out. Because the whole pen/touch/pad/
> battery chain runs unconditionally per branch, a single up-front check
> against the maximum offset (286 bytes for INTUOSP2_BT/INTUOSP2S_BT,
> 46 bytes for the gen3 branch) bounds every sub-parser. Returning 0 on
> a short report also skips those calls for the same malformed report,
> which is the safe, conservative behavior.
> 
> Fixes: 4922cd26f03c ("HID: wacom: Support 2nd-gen Intuos Pro's Bluetooth classic interface")
> Cc: [email protected]
> Signed-off-by: Ibrahim Hashimov <[email protected]>
> Assisted-by: AuditCode-AI:2026.07
> ---
> v2: the v1 check (len < 109 / len < 43) only bounded
>     wacom_intuos_pro2_bt_pen(). As sashiko-bot pointed out, the
>     unconditional touch/pad/battery calls read much further --
>     wacom_intuos_pro2_bt_pad() up to data[285] and
>     wacom_intuos_gen3_bt_battery() up to data[45] -- so a report in the
>     gap (109..285 / 43..45) passed the guard yet still over-read. Raise
>     the minimums to the furthest offset each branch dereferences
>     (286 / 46) so the guard actually bounds the whole call chain.
> 
>  drivers/hid/wacom_wac.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c
> index da1f0ea85625..89a191cf1924 100644
> --- a/drivers/hid/wacom_wac.c
> +++ b/drivers/hid/wacom_wac.c
> @@ -1548,6 +1548,19 @@ static int wacom_intuos_pro2_bt_irq(struct wacom_wac *wacom, size_t len)
>  		return 0;
>  	}
>  
> +	if (wacom->features.type == INTUOSP2_BT ||
> +	    wacom->features.type == INTUOSP2S_BT) {
> +		if (len < 286) {
> +			dev_warn(wacom->pen_input->dev.parent,
> +				 "Pro2 BT report too short: %zu bytes\n", len);
> +			return 0;
> +		}
> +	} else if (len < 46) {
> +		dev_warn(wacom->pen_input->dev.parent,
> +			 "Pro2 BT report too short: %zu bytes\n", len);
> +		return 0;
> +	}
> +
>  	wacom_intuos_pro2_bt_pen(wacom);
>  	if (wacom->features.type == INTUOSP2_BT ||
>  	    wacom->features.type == INTUOSP2S_BT) {
> -- 
> 2.50.1 (Apple Git-155)
>