Re: [PATCH] Input: cs40l50-vibra - validate custom data from user space

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Sat, Jul 18, 2026 at 04:40:32PM +0900, HyeongJun An wrote:
> cs40l50_add() copies the custom data of an FF_PERIODIC/FF_CUSTOM effect
> straight from the ff_effect the user passed to EVIOCSFF, without
> requiring it to hold anything:
> 
>     work_data.custom_data = memdup_array_user(periodic->custom_data,
>                                               periodic->custom_len,
>                                               sizeof(s16));
>     work_data.custom_len = periodic->custom_len;
> 
> The driver then reads two words out of that buffer: custom_data[0] as the
> waveform bank in cs40l50_effect_bank_set(), and custom_data[1] as the
> index within the bank in cs40l50_effect_index_set().  Neither read is
> covered by a length check, and custom_len is fully user controlled:
> 
>   - custom_len == 0 makes memdup_array_user() call memdup_user() with a
>     length of zero, which returns ZERO_SIZE_PTR rather than an error, so
>     custom_data[0] dereferences it.
> 
>   - custom_len == 1 allocates two bytes.  A bank of ROM or RAM keeps
>     effect->type out of the OWT case, and custom_data[1] is then read one
>     word past the allocation.
> 
> The bank value itself is also mishandled.  It is masked with
> CS40L50_CUSTOM_DATA_MASK (0xffff) but stored in an s16, so a
> custom_data[0] of 0x8000 or above wraps to a negative value that passes
> the "bank_type >= CS40L50_WVFRM_BANK_NUM" test.
> cs40l50_effect_index_set() indexes vib->dsp.banks[] with it before the
> switch statement's default case gets a chance to reject it:
> 
>     base_index = vib->dsp.banks[effect->type].base_index;
>     max_index = vib->dsp.banks[effect->type].max_index;
> 
> Require the two words the driver reads to be present, and hold the masked
> bank in a u32 so the existing upper-bound test covers the whole range.
> The da7280 haptic driver already range checks custom_len this way.
> 
> Fixes: c38fe1bb5d21 ("Input: cs40l50 - Add support for the CS40L50 haptic driver")
> Cc: stable@vger.kernel.org
> Assisted-by: Claude:claude-opus-4-8
> Signed-off-by: HyeongJun An <sammiee5311@gmail.com>

Applied, thank you.

-- 
Dmitry