Re: [PATCH v2] ACPI: pfr_update: fix stack buffer overflow in query_capability()

On Fri, Aug 7, 2026 at 4:40 PM Anirudh Prasad <[email protected]> wrote:
>
> query_capability() copies four ACPI buffer objects returned by the
> firmware _DSM into fixed-size u8[16] fields in struct
> pfru_update_cap_info using memcpy with the firmware-supplied length:
>
>   memcpy(&cap_hdr->code_type,
>          elements[CAP_CODE_TYPE_IDX].buffer.pointer,
>          elements[CAP_CODE_TYPE_IDX].buffer.length);
>
> The same pattern repeats for drv_type, platform_id, and oem_id.
> If the firmware returns buffer.length > 16 for any of these fields,
> memcpy writes past the destination array.
>
> struct pfru_update_cap_info is stack-allocated in pfru_ioctl().
> Confirmed with KASAN on 7.2-rc6: three stack-out-of-bounds reports
> are generated when a DSM returns 64-byte buffers, with writes reaching
> 44 bytes past the end of cap_hdr's [64, 156) frame window into
> adjacent stack redzones.
>
> Fix by validating each buffer length against its destination field
> size before copying, and returning -EINVAL if the firmware supplies
> an oversized buffer.
>
> Fixes: 0db89fa243e5 ("ACPI: Introduce Platform Firmware Runtime Update device driver")
> Cc: [email protected]
> Signed-off-by: Anirudh Prasad <[email protected]>
> ---
>  drivers/acpi/pfr_update.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/drivers/acpi/pfr_update.c b/drivers/acpi/pfr_update.c
> index 6283105bb0e8..e14e053cea44 100644
> --- a/drivers/acpi/pfr_update.c
> +++ b/drivers/acpi/pfr_update.c
> @@ -158,6 +158,14 @@ static int query_capability(struct pfru_update_cap_info *cap_hdr,
>                 goto free_acpi_buffer;
>         }
>
> +       if (out_obj->package.elements[CAP_CODE_TYPE_IDX].buffer.length > sizeof(cap_hdr->code_type) ||
> +           out_obj->package.elements[CAP_DRV_TYPE_IDX].buffer.length > sizeof(cap_hdr->drv_type) ||
> +           out_obj->package.elements[CAP_PLAT_ID_IDX].buffer.length > sizeof(cap_hdr->platform_id) ||
> +           out_obj->package.elements[CAP_OEM_ID_IDX].buffer.length > sizeof(cap_hdr->oem_id)) {

The lines above are too long.

Please introduce a helper pointer to the elements array, say "elem =
out_obj->package.elements", and use if in these checks.

> +               ret = -EINVAL;
> +               goto free_acpi_buffer;
> +       }
> +
>         cap_hdr->update_cap = out_obj->package.elements[CAP_UPDATE_IDX].integer.value;
>         memcpy(&cap_hdr->code_type,
>                out_obj->package.elements[CAP_CODE_TYPE_IDX].buffer.pointer,
> --
> 2.55.0
>
>
>