Re: [PATCH v2 1/4] usb: typec: ucsi: Fix null deref in trace

[Dmitry Baryshkov <dmitry.baryshkov@linaro.org>]

On Wed, 24 Apr 2024 at 04:48, Jameson Thies <jthies@google.com> wrote:
>
> From: Abhishek Pandit-Subedi <abhishekpandit@chromium.org>
>
> ucsi_register_altmode checks IS_ERR on returned pointer and treats
> NULL as valid. This results in a null deref when
> trace_ucsi_register_altmode is called. Return an error from
> ucsi_register_displayport when it is not supported and register the
> altmode with typec_port_register_altmode.
>
> Reviewed-by: Jameson Thies <jthies@google.com>
> Signed-off-by: Abhishek Pandit-Subedi <abhishekpandit@chromium.org>
> ---
> Changes in V2:
> - Checks for error response from ucsi_register_displayport when
> registering DisplayPort alternate mode.
>
>  drivers/usb/typec/ucsi/ucsi.c | 3 +++
>  drivers/usb/typec/ucsi/ucsi.h | 2 +-
>  2 files changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/usb/typec/ucsi/ucsi.c b/drivers/usb/typec/ucsi/ucsi.c
> index cb52e7b0a2c5c..f3b413f94fd28 100644
> --- a/drivers/usb/typec/ucsi/ucsi.c
> +++ b/drivers/usb/typec/ucsi/ucsi.c
> @@ -361,6 +361,9 @@ static int ucsi_register_altmode(struct ucsi_connector *con,
>                 switch (desc->svid) {
>                 case USB_TYPEC_DP_SID:
>                         alt = ucsi_register_displayport(con, override, i, desc);
> +                       if (IS_ERR(alt) && PTR_ERR(alt) == -EOPNOTSUPP)

This makes it ignore EOPNOTSUPP if it is returned by the non-stub
implementation. I think the current state is actually better than the
implementation found in this patch. I'd suggest adding a comment to
ucsi_register_displayport() stub instead.

> +                               alt = typec_port_register_altmode(con->port, desc);
> +
>                         break;
>                 case USB_TYPEC_NVIDIA_VLINK_SID:
>                         if (desc->vdo == USB_TYPEC_NVIDIA_VLINK_DBG_VDO)
> diff --git a/drivers/usb/typec/ucsi/ucsi.h b/drivers/usb/typec/ucsi/ucsi.h
> index c4d103db9d0f8..c663dce0659ee 100644
> --- a/drivers/usb/typec/ucsi/ucsi.h
> +++ b/drivers/usb/typec/ucsi/ucsi.h
> @@ -496,7 +496,7 @@ ucsi_register_displayport(struct ucsi_connector *con,
>                           bool override, int offset,
>                           struct typec_altmode_desc *desc)
>  {
> -       return NULL;
> +       return ERR_PTR(-EOPNOTSUPP);
>  }
>
>  static inline void
> --
> 2.44.0.769.g3c40516874-goog
>


-- 
With best wishes
Dmitry