Re: [PATCH v4] usb: typec: bus: verify partner exists in typec_altmode_attention

[Guenter Roeck]

On Mon, Aug 14, 2023 at 06:05:59PM +0000, RD Babiera wrote:
> Some usb hubs will negotiate DisplayPort Alt mode with the device
> but will then negotiate a data role swap after entering the alt
> mode. The data role swap causes the device to unregister all alt
> modes, however the usb hub will still send Attention messages
> even after failing to reregister the Alt Mode. type_altmode_attention
> currently does not verify whether or not a device's altmode partner
> exists, which results in a NULL pointer error when dereferencing
> the typec_altmode and typec_altmode_ops belonging to the altmode
> partner.
> 
> Verify the presence of a device's altmode partner before sending
> the Attention message to the Alt Mode driver.
> 
> Fixes: 8a37d87d72f0 ("usb: typec: Bus type for alternate modes")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: RD Babiera <rdbabiera@xxxxxxxxxx>

Reviewed-by: Guenter Roeck <linux@xxxxxxxxxxxx>

> ---
> Changes since v1:
> * Only assigns pdev if altmode partner exists in typec_altmode_attention
> * Removed error return in typec_altmode_attention if Alt Mode does
>   not implement Attention messages.
> * Changed tcpm_log message to indicate that altmode partner does not exist,
>   as it only logs in that case.
> ---
> Changes since v2:
> * Changed tcpm_log message to accurately reflect error
> * Revised commit message
> ---
> Changes since v3:
> * Fixed nits
> ---
>  drivers/usb/typec/bus.c           | 12 ++++++++++--
>  drivers/usb/typec/tcpm/tcpm.c     |  3 ++-
>  include/linux/usb/typec_altmode.h |  2 +-
>  3 files changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/usb/typec/bus.c b/drivers/usb/typec/bus.c
> index fe5b9a2e61f5..e95ec7e382bb 100644
> --- a/drivers/usb/typec/bus.c
> +++ b/drivers/usb/typec/bus.c
> @@ -183,12 +183,20 @@ EXPORT_SYMBOL_GPL(typec_altmode_exit);
>   *
>   * Notifies the partner of @adev about Attention command.
>   */
> -void typec_altmode_attention(struct typec_altmode *adev, u32 vdo)
> +int typec_altmode_attention(struct typec_altmode *adev, u32 vdo)
>  {
> -	struct typec_altmode *pdev = &to_altmode(adev)->partner->adev;
> +	struct altmode *partner = to_altmode(adev)->partner;
> +	struct typec_altmode *pdev;
> +
> +	if (!partner)
> +		return -ENODEV;
> +
> +	pdev = &partner->adev;
>  
>  	if (pdev->ops && pdev->ops->attention)
>  		pdev->ops->attention(pdev, vdo);
> +
> +	return 0;
>  }
>  EXPORT_SYMBOL_GPL(typec_altmode_attention);
>  
> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> index 5a7d8cc04628..77fe16190766 100644
> --- a/drivers/usb/typec/tcpm/tcpm.c
> +++ b/drivers/usb/typec/tcpm/tcpm.c
> @@ -1877,7 +1877,8 @@ static void tcpm_handle_vdm_request(struct tcpm_port *port,
>  			}
>  			break;
>  		case ADEV_ATTENTION:
> -			typec_altmode_attention(adev, p[1]);
> +			if (typec_altmode_attention(adev, p[1]))
> +				tcpm_log(port, "typec_altmode_attention no port partner altmode");
>  			break;
>  		}
>  	}
> diff --git a/include/linux/usb/typec_altmode.h b/include/linux/usb/typec_altmode.h
> index 350d49012659..28aeef8f9e7b 100644
> --- a/include/linux/usb/typec_altmode.h
> +++ b/include/linux/usb/typec_altmode.h
> @@ -67,7 +67,7 @@ struct typec_altmode_ops {
>  
>  int typec_altmode_enter(struct typec_altmode *altmode, u32 *vdo);
>  int typec_altmode_exit(struct typec_altmode *altmode);
> -void typec_altmode_attention(struct typec_altmode *altmode, u32 vdo);
> +int typec_altmode_attention(struct typec_altmode *altmode, u32 vdo);
>  int typec_altmode_vdm(struct typec_altmode *altmode,
>  		      const u32 header, const u32 *vdo, int count);
>  int typec_altmode_notify(struct typec_altmode *altmode, unsigned long conf,
> 
> base-commit: f176638af476c6d46257cc3303f5c7cf47d5967d
> -- 
> 2.41.0.694.ge786442a9b-goog
>