Re: [PATCH] HID: core: fix number/pointer type confusion on long items

On Fri, 3 Jul 2026, Jann Horn wrote:

> When fetch_item() is called by hid_scan_report() on an item with
> HID_ITEM_TAG_LONG, it stores a pointer to the item data in
> item->data.longdata instead of storing a value directly in
> item->data.{u8/u16/u32}.
> 
> When item_udata() or item_sdata() encounters such an item, it incorrectly
> assumes that the item is in short format, and therefore returns the lower
> part of a kernel pointer reinterpreted as a number.
> 
> When a HID device is connected whose descriptor contains a
> HID_GLOBAL_ITEM_TAG_REPORT_SIZE encoded in long format with size=4, this
> causes the lower half of a kernel pointer to be printed into dmesg as a
> number, like this:
> 
>     hid (null): invalid report_size 107953555
> 
> To fix it, let item_udata() and item_sdata() verify that the item is in
> short format.
> 
> Note that this bug only affects hid_scan_report(), while the main parsing
> pass hid_parse_collections() will always bail out when encountering a long
> item.
> 
> Sidenote: There are currently no users of data.longdata; maybe we should
> just remove any parsing of long-format descriptors as a follow-up.
> 
> Fixes: 3dc8fc083dbf ("HID: Use hid_parser for pre-scanning the report descriptors")
> Cc: [email protected]
> Signed-off-by: Jann Horn <[email protected]>

Applied, thanks Jann.

-- 
Jiri Kosina
SUSE Labs