Re: [PATCH v3] usb: typec: bus: verify partner exists in typec_altmode_attention

[Guenter Roeck <linux@roeck-us.net>]

On 8/11/23 14:37, 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@vger.kernel.org
> Signed-off-by: RD Babiera <rdbabiera@google.com>
> ---
> 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

IMO the log message should be "no port partner", but I don't want this
to go on forever.

Reviewed-by: Guenter Roeck <linux@roeck-us.net>

> ---
>   drivers/usb/typec/bus.c           | 12 ++++++++++--
>   drivers/usb/typec/tcpm/tcpm.c     |  5 ++++-
>   include/linux/usb/typec_altmode.h |  2 +-
>   3 files changed, 15 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..97b7b22e9cf1 100644
> --- a/drivers/usb/typec/tcpm/tcpm.c
> +++ b/drivers/usb/typec/tcpm/tcpm.c
> @@ -1791,6 +1791,7 @@ static void tcpm_handle_vdm_request(struct tcpm_port *port,
>   	u32 p[PD_MAX_PAYLOAD];
>   	u32 response[8] = { };
>   	int i, rlen = 0;
> +	int ret;
>   
>   	for (i = 0; i < cnt; i++)
>   		p[i] = le32_to_cpu(payload[i]);
> @@ -1877,7 +1878,9 @@ static void tcpm_handle_vdm_request(struct tcpm_port *port,
>   			}
>   			break;
>   		case ADEV_ATTENTION:
> -			typec_altmode_attention(adev, p[1]);
> +			ret = typec_altmode_attention(adev, p[1]);
> +			if (ret)
> +				tcpm_log(port, "typec_altmode_attention NULL 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