Re: [PATCH v3] usb: typec: altmodes/displayport: create sysfs nodes as driver's default device attribute group

[Heikki Krogerus]

On Thu, Feb 29, 2024 at 12:11:02AM +0000, RD Babiera wrote:
> The DisplayPort driver's sysfs nodes may be present to the userspace before
> typec_altmode_set_drvdata() completes in dp_altmode_probe. This means that
> a sysfs read can trigger a NULL pointer error by deferencing dp->hpd in
> hpd_show or dp->lock in pin_assignment_show, as dev_get_drvdata() returns
> NULL in those cases.
> 
> Remove manual sysfs node creation in favor of adding attribute group as
> default for devices bound to the driver. The ATTRIBUTE_GROUPS() macro is
> not used here otherwise the path to the sysfs nodes is no longer compliant
> with the ABI.
> 
> Fixes: 0e3bb7d6894d ("usb: typec: Add driver for DisplayPort alternate mode")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: RD Babiera <rdbabiera@xxxxxxxxxx>

Reviewed-by: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>

> ---
> Changes from v1:
> * Moved sysfs node creation instead of NULL checking dev_get_drvdata().
> Changes from v2:
> * Removed manual sysfs node creation, now added as default device group in
> driver.
> ---
>  drivers/usb/typec/altmodes/displayport.c | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/us<F16>b/typec/altmodes/displayport.c b/drivers/usb/typec/altmodes/displayport.c
> index 5a80776c7255..94e1b43a862d 100644
> --- a/drivers/usb/typec/altmodes/displayport.c
> +++ b/drivers/usb/typec/altmodes/displayport.c
> @@ -702,16 +702,21 @@ static ssize_t hpd_show(struct device *dev, struct device_attribute *attr, char
>  }
>  static DEVICE_ATTR_RO(hpd);
>  
> -static struct attribute *dp_altmode_attrs[] = {
> +static struct attribute *displayport_attrs[] = {
>  	&dev_attr_configuration.attr,
>  	&dev_attr_pin_assignment.attr,
>  	&dev_attr_hpd.attr,
>  	NULL
>  };
>  
> -static const struct attribute_group dp_altmode_group = {
> +static const struct attribute_group displayport_group = {
>  	.name = "displayport",
> -	.attrs = dp_altmode_attrs,
> +	.attrs = displayport_attrs,
> +};
> +
> +static const struct attribute_group *displayport_groups[] = {
> +	&displayport_group,
> +	NULL,
>  };
>  
>  int dp_altmode_probe(struct typec_altmode *alt)
> @@ -720,7 +725,6 @@ int dp_altmode_probe(struct typec_altmode *alt)
>  	struct typec_altmode *plug = typec_altmode_get_plug(alt, TYPEC_PLUG_SOP_P);
>  	struct fwnode_handle *fwnode;
>  	struct dp_altmode *dp;
> -	int ret;
>  
>  	/* FIXME: Port can only be DFP_U. */
>  
> @@ -731,10 +735,6 @@ int dp_altmode_probe(struct typec_altmode *alt)
>  	      DP_CAP_PIN_ASSIGN_DFP_D(alt->vdo)))
>  		return -ENODEV;
>  
> -	ret = sysfs_create_group(&alt->dev.kobj, &dp_altmode_group);
> -	if (ret)
> -		return ret;
> -
>  	dp = devm_kzalloc(&alt->dev, sizeof(*dp), GFP_KERNEL);
>  	if (!dp)
>  		return -ENOMEM;
> @@ -777,7 +777,6 @@ void dp_altmode_remove(struct typec_altmode *alt)
>  {
>  	struct dp_altmode *dp = typec_altmode_get_drvdata(alt);
>  
> -	sysfs_remove_group(&alt->dev.kobj, &dp_altmode_group);
>  	cancel_work_sync(&dp->work);
>  	typec_altmode_put_plug(dp->plug_prime);
>  
> @@ -803,6 +802,7 @@ static struct typec_altmode_driver dp_altmode_driver = {
>  	.driver = {
>  		.name = "typec_displayport",
>  		.owner = THIS_MODULE,
> +		.dev_groups = displayport_groups,
>  	},
>  };
>  module_typec_altmode_driver(dp_altmode_driver);
> 
> base-commit: a560a5672826fc1e057068bda93b3d4c98d037a2
> -- 
> 2.44.0.rc1.240.g4c46232300-goog

-- 
heikki