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

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Message-ID: <20240229001101.3889432-2-rdbabiera@google.com>
Date: Thu, 29 Feb 2024 00:11:02 +0000
From: RD Babiera <rdbabiera@...gle.com>
To: rdbabiera@...gle.com, heikki.krogerus@...ux.intel.com, 
	gregkh@...uxfoundation.org
Cc: badhri@...gle.com, linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org, 
	stable@...r.kernel.org
Subject: [PATCH v3] usb: typec: altmodes/displayport: create sysfs nodes as
 driver's default device attribute group

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@...r.kernel.org
Signed-off-by: RD Babiera <rdbabiera@...gle.com>
---
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/usb/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