On Wed, 16 Dec 2020, Randy Dunlap wrote:
> Prevent invalid (0, 0) inputs to hid-core's snto32() function.
>
> Maybe it is just the dummy device here that is causing this, but
> there are hundreds of calls to snto32(0, 0). Having n (bits count)
> of 0 is causing the current UBSAN trap with a shift value of
> 0xffffffff (-1, or n - 1 in this function).
>
> Either of the value to shift being 0 or the bits count being 0 can be
> handled by just returning 0 to the caller, avoiding the following
> complex shift + OR operations:
>
> return value & (1 << (n - 1)) ? value | (~0U << n) : value;
>
> Fixes: dde5845a529f ("[PATCH] Generic HID layer - code split")
> Signed-off-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> Reported-by: syzbot+1e911ad71dd4ea72e04a@xxxxxxxxxxxxxxxxxxxxxxxxx
> Cc: Jiri Kosina <jikos@xxxxxxxxxx>
> Cc: Benjamin Tissoires <benjamin.tissoires@xxxxxxxxxx>
> Cc: linux-input@xxxxxxxxxxxxxxx
> ---
> drivers/hid/hid-core.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> --- lnx-510.orig/drivers/hid/hid-core.c
> +++ lnx-510/drivers/hid/hid-core.c
> @@ -1307,6 +1307,9 @@ EXPORT_SYMBOL_GPL(hid_open_report);
>
> static s32 snto32(__u32 value, unsigned n)
> {
> + if (!value || !n)
> + return 0;
> +
Given the fact that this has been in the code basically since ever, we're
probably fine, but it's good to have this fixed nevertheless. Applied
conservatively to hid.git#for-5.12/core.
Thanks,
--
Jiri Kosina
SUSE Labs
