Re: [PATCH v2] platform/chrome: cros_ec_typec: reject out-of-bounds PD cap count

[Andrei Kuchynski]

On Thu, Jun 25, 2026 at 3:01 PM Maoyi Xie <maoyixie.tju@xxxxxxxxx> 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. 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 EC source arrays are only
> seven entries wide. A larger count reads past them too.
>
> The ChromeOS EC firmware caps these counts today, so a compliant setup
> does not hit this. The kernel should still validate these values rather
> than trust them.
>
> Validate the counts in cros_typec_register_partner_pdos() next to the
> memcpy. Skip the PDO registration if either count is above PDO_MAX_OBJECTS.
> The rest of cros_typec_handle_status() still runs so events are handled
> and cleared.
>
> Fixes: 348a2e8c93d3 ("platform/chrome: cros_ec_typec: Register partner PDOs")
> Suggested-by: Tzung-Bi Shih <tzungbi@xxxxxxxxxx>
> Suggested-by: Andrei Kuchynski <akuchynski@xxxxxxxxxxxx>
> Co-developed-by: Kaixuan Li <kaixuan.li@xxxxxxxxxx>
> Signed-off-by: Kaixuan Li <kaixuan.li@xxxxxxxxxx>
> Signed-off-by: Maoyi Xie <maoyixie.tju@xxxxxxxxx>

Reviewed-by: Andrei Kuchynski <akuchynski@xxxxxxxxxxxx>


> ---
> v2: Move the check into cros_typec_register_partner_pdos() next to the
>     memcpy it guards. v1 put it at the top of cros_typec_handle_status()
>     and returned early. That skipped the rest of the status handling and
>     left events uncleared.
>
> v1: https://lore.kernel.org/r/178229037114.3009621.14045345257767446805@xxxxxxxxxxxx
>
>  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..50a68819ceb7 100644
> --- a/drivers/platform/chrome/cros_ec_typec.c
> +++ b/drivers/platform/chrome/cros_ec_typec.c
> @@ -1119,6 +1119,12 @@ static void cros_typec_register_partner_pdos(struct cros_typec_data *typec,
>         if (!resp->source_cap_count && !resp->sink_cap_count)
>                 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;
> +       }
> +
>         port->partner_pd = typec_partner_usb_power_delivery_register(port->partner, &desc);
>         if (IS_ERR(port->partner_pd)) {
>                 dev_warn(typec->dev, "Failed to register partner PD device, port: %d\n", port_num);