Re: [PATCH] platform/chrome: cros_ec_typec: reject out-of-bounds PD cap count

On Wed, Jun 24, 2026 at 10:39 AM Maoyi Xie <[email protected]> wrote:
>
> cros_typec_register_partner_pdos() copies the partner PDOs from the EC
> TYPEC_STATUS response into the fixed caps_desc.pdo[PDO_MAX_OBJECTS] array.
>
>         memcpy(caps_desc.pdo, resp->source_cap_pdos,
>                sizeof(u32) * resp->source_cap_count);
>         ...
>         memcpy(caps_desc.pdo, resp->sink_cap_pdos,
>                sizeof(u32) * resp->sink_cap_count);
>
> PDO_MAX_OBJECTS is 7. source_cap_count and sink_cap_count are u8 fields
> from the EC, and the only check is that they are not both zero. If either
> is larger than 7, the memcpy writes past the end of the array on the stack.
> A count of 255 overflows it by about 1 KB.
>
> The ChromeOS EC firmware caps these counts today, so a compliant setup
> does not hit this. The kernel should still validate the values from the EC
> rather than trust them.
>
> Validate the counts in cros_typec_handle_status() right after the
> EC_CMD_TYPEC_STATUS command returns, and return early if either one is
> above PDO_MAX_OBJECTS.
>
> Fixes: 348a2e8c93d3 ("platform/chrome: cros_ec_typec: Register partner PDOs")
> Suggested-by: Tzung-Bi Shih <[email protected]>
> Co-developed-by: Kaixuan Li <[email protected]>
> Signed-off-by: Kaixuan Li <[email protected]>
> Signed-off-by: Maoyi Xie <[email protected]>
> ---
>  drivers/platform/chrome/cros_ec_typec.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/drivers/platform/chrome/cros_ec_typec.c b/drivers/platform/chrome/cros_ec_typec.c
> index c0806c562bb9..3ae9b35b7d85 100644
> --- a/drivers/platform/chrome/cros_ec_typec.c
> +++ b/drivers/platform/chrome/cros_ec_typec.c
> @@ -1158,6 +1158,12 @@ static void cros_typec_handle_status(struct cros_typec_data *typec, int port_num
>                 return;
>         }
>
> +       if (resp.source_cap_count > PDO_MAX_OBJECTS ||
> +           resp.sink_cap_count > PDO_MAX_OBJECTS) {
> +               dev_warn(typec->dev, "Invalid PDO count from EC, port: %d\n", port_num);
> +               return;
> +       }
> +

Hi Maoyi,

Thanks for the patch.
Are we only rejecting `out-of-bounds PD cap count` here?

>         /* If we got a hard reset, unregister everything and return. */
>         if (resp.events & PD_STATUS_EVENT_HARD_RESET) {
>                 cros_typec_remove_partner(typec, port_num);

Thanks,
Andrei