[PATCH v7 0/3] leds: trigger: netdev: fix sysfs_update_group() races

[PATCH v7 0/3] leds: trigger: netdev: fix sysfs_update_group() races

[A. Sverdlin]

From: Alexander Sverdlin <alexander.sverdlin@siemens.com>

The netdev LED trigger refreshes the link_speed attribute group with
sysfs_update_group() from several contexts (the NETDEV_CHANGE notifier,
device_name writes and, indirectly, trigger (de)activation) that share no
common lock. On a board that emits PHY link events while the trigger is
being (re)armed during boot this is observed as a hard sysfs failure:

  sysfs: cannot create duplicate filename '...green:lan/link_10'
  ...
  led_trigger_set
  led_trigger_write

The window between activate() and device_add_groups() in led_trigger_set()
is narrow, so to reproduce it reliably I artificially widened it with the
debug patch below:

--- a/drivers/leds/led-triggers.c
+++ b/drivers/leds/led-triggers.c
@@ -12,6 +12,7 @@
 #include <linux/list.h>
 #include <linux/spinlock.h>
 #include <linux/device.h>
+#include <linux/delay.h>
 #include <linux/timer.h>
 #include <linux/rwsem.h>
 #include <linux/leds.h>
@@ -223,6 +224,8 @@ int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
 		if (ret)
 			goto err_activate;

+		msleep(5000);
+
 		ret = device_add_groups(led_cdev->dev, trig->groups);
 		if (ret) {
 			dev_err(led_cdev->dev, "Failed to add trigger attributes\n");

With that msleep() in place, writing the trigger while a NETDEV_CHANGE is
delivered from the linkwatch workqueue reproduces the duplicate-filename
splat every time.

The whole series is LOCKDEP-verified.

Changelog:
v7:
- rebased onto for-leds-next as of 687615faae92
- dropped patches 2 and 5 superseded by Lee's be29a52d48b5
- added Lee's tags into patches 1-2, but not patch 3 as it was changed
  substantially in rebase
v6:
- report invalid interval to user space
- fixed unlocked hw_control check in interval_store()
- added missing carrier_link_up check in netdev_trig_sw_blink()
- https://lore.kernel.org/all/20261027113349.383147-1-alexander.sverdlin@siemens.com/
v5:
- removed unset_device_name()
- https://lore.kernel.org/all/20261020124651.1987272-1-alexander.sverdlin@siemens.com/
v4:
- introduced netdev_trig_sw_blink() and used it in netdev_trig_work()
- https://lore.kernel.org/all/20261001131206.2513248-1-alexander.sverdlin@siemens.com/
v3:
- introduced unset_device_name() as a counterpart of set_device_name()
- guard() has been converted to either explicit mutex_lock()/mutex_unlock()
  or scoped_guard()
- rebased onto next-20260925
- https://lore.kernel.org/all/20260929120902.2793138-1-alexander.sverdlin@siemens.com/
v2:
- addressed pre-existing issues found by Sashiko (patches 1&2)
- reduced verbosity both in comments and in commit messages
- patch 3 is a combined rework of patches 1&2 from v1
- dropped sync from cancel_delayed_work() (worker now takes the lock)
- https://lore.kernel.org/all/20260921093249.3481413-1-alexander.sverdlin@siemens.com/
v1:
- https://lore.kernel.org/all/20260914132356.807004-1-alexander.sverdlin@siemens.com/

Alexander Sverdlin (3):
  leds: trigger: netdev: Put netdev on activate error path
  leds: trigger: netdev: Fix sysfs_update_group() races
  leds: trigger: netdev: Report invalid interval to user space

 drivers/leds/trigger/ledtrig-netdev.c | 83 +++++++++++++++++----------
 1 file changed, 53 insertions(+), 30 deletions(-)

-- 
2.56.0

[PATCH v7 1/3] leds: trigger: netdev: Put netdev on activate error path

[A. Sverdlin]

From: Alexander Sverdlin <alexander.sverdlin@siemens.com>

When hw control is active, set_device_name() takes a reference on the
netdev via dev_get_by_name(). The register_netdevice_notifier() failure
path frees trigger_data without dropping it, leaking the netdev.

Cc: stable@vger.kernel.org
Closes: https://lore.kernel.org/all/20260914140045.B8F4C1F000FF@smtp.kernel.org/
Fixes: 0316cc5629d1 ("leds: trigger: netdev: init mode if hw control already active")
Acked-by: Lee Jones <lee@kernel.org>
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
---
Changelog:
v5:
- removed unset_device_name()
v3:
- introduced unset_device_name() as a counterpart of set_device_name()

 drivers/leds/trigger/ledtrig-netdev.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/leds/trigger/ledtrig-netdev.c b/drivers/leds/trigger/ledtrig-netdev.c
index 9fa56ac523c7d..2afe7372aad78 100644
--- a/drivers/leds/trigger/ledtrig-netdev.c
+++ b/drivers/leds/trigger/ledtrig-netdev.c
@@ -795,8 +795,10 @@ static int netdev_trig_activate(struct led_classdev *led_cdev)
 	led_set_trigger_data(led_cdev, trigger_data);
 
 	rc = register_netdevice_notifier(&trigger_data->notifier);
-	if (rc)
+	if (rc) {
+		dev_put(trigger_data->net_dev);
 		kfree(trigger_data);
+	}
 
 	return rc;
 }
-- 
2.56.0

Re: [PATCH v7 1/3] leds: trigger: netdev: Put netdev on activate error path

[sashiko-bot]

> From: Alexander Sverdlin <alexander.sverdlin@siemens.com>
> 
> When hw control is active, set_device_name() takes a reference on the
> netdev via dev_get_by_name(). The register_netdevice_notifier() failure
> path frees trigger_data without dropping it, leaking the netdev.
> 
> Cc: stable@vger.kernel.org
> Closes: https://lore.kernel.org/all/20260914140045.B8F4C1F000FF@smtp.kernel.org/
> Fixes: 0316cc5629d1 ("leds: trigger: netdev: init mode if hw control already active")
> Acked-by: Lee Jones <lee@kernel.org>
> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>

Sashiko has reviewed this patch and found no issues.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261113201936.2645736-1-alexander.sverdlin@siemens.com?part=1

[PATCH v7 2/3] leds: trigger: netdev: Fix sysfs_update_group() races

[A. Sverdlin]

From: Alexander Sverdlin <alexander.sverdlin@siemens.com>

The link_speed attribute group was listed in netdev_led_trigger.groups,
so the LED core creates and destroys it via device_add_groups() /
device_remove_groups() in led_trigger_set() (under trigger_lock), while
the trigger also refreshes it with sysfs_update_group() from
netdev_trig_notify() and device_name writes. With no shared lock this was
observed as a sysfs splat when the trigger is re-armed during PHY link-up:

  sysfs: cannot create duplicate filename '...green:lan/link_10'

    CPU 0 (led_trigger_set)        CPU 1 (linkwatch workqueue)
    -----------------------        ---------------------------
    activate():
      register_netdevice_notifier()
    .                              netdev_trig_notify(NETDEV_CHANGE):
    .                                sysfs_update_group() creates "link_10"
    device_add_groups()
      creates "link_10"  <- EEXIST!

The mirror case (device_remove_groups() racing the notifier) leaves an
orphaned sysfs file pointing at freed trigger_data, i.e. a UAF.

Manage the group in the trigger: drop it from netdev_led_trigger.groups
and create/destroy it in activate()/deactivate(), so the LED core never
touches it. The two remaining refreshers, netdev_trig_notify() and
device_name_store(), are serialized against each other by a dedicated
attr_lock, and the is_visible callback takes trigger_data->lock for its
supported_link_modes read. sysfs_update_group() is never called under
trigger_data->lock, so it cannot deadlock against a concurrent link_*
store that takes that lock.

Cc: stable@vger.kernel.org
Fixes: 06cdca014eca ("leds: trigger: netdev: Display only supported link speed attribute")
Acked-by: Lee Jones <lee@kernel.org>
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
---
Changelog:
v3:
- changed guard() to scoped_guard() and dev_put() to unset_device_name()
v2:
- this patch is a combined rework of patches 1&2 from v1

 drivers/leds/trigger/ledtrig-netdev.c | 74 +++++++++++++++++----------
 1 file changed, 47 insertions(+), 27 deletions(-)

diff --git a/drivers/leds/trigger/ledtrig-netdev.c b/drivers/leds/trigger/ledtrig-netdev.c
index 2afe7372aad78..601c4d9e0198a 100644
--- a/drivers/leds/trigger/ledtrig-netdev.c
+++ b/drivers/leds/trigger/ledtrig-netdev.c
@@ -57,6 +57,8 @@
 
 struct led_netdev_data {
 	struct mutex lock;
+	/* Serializes link_speed group refreshes; never taken by attr stores */
+	struct mutex attr_lock;
 
 	struct delayed_work work;
 	struct notifier_block notifier;
@@ -338,8 +340,9 @@ static ssize_t device_name_store(struct device *dev,
 	if (ret < 0)
 		return ret;
 
-	/* Refresh link_speed visibility */
-	sysfs_update_group(&dev->kobj, &netdev_trig_link_speed_attrs_group);
+	/* Serialize the link_speed visibility refresh against netdev_trig_notify() */
+	scoped_guard(mutex, &trigger_data->attr_lock)
+		sysfs_update_group(&dev->kobj, &netdev_trig_link_speed_attrs_group);
 
 	return size;
 }
@@ -561,22 +564,23 @@ static umode_t netdev_trig_link_speed_visible(struct kobject *kobj,
 	 * Stop at the first matching entry as we care only to check if a particular
 	 * speed is supported and not the kind.
 	 */
-	for_each_set_bit(mode, supported_link_modes, __ETHTOOL_LINK_MODE_MASK_NBITS) {
-		struct ethtool_link_ksettings link_ksettings;
-
-		ethtool_params_from_link_mode(&link_ksettings, mode);
-
-		CHECK_LINK_MODE_ATTR(10);
-		CHECK_LINK_MODE_ATTR(100);
-		CHECK_LINK_MODE_ATTR(1000);
-		CHECK_LINK_MODE_ATTR(2500);
-		CHECK_LINK_MODE_ATTR(5000);
-		CHECK_LINK_MODE_ATTR(10000);
-		CHECK_LINK_MODE_ATTR(25000);
-		CHECK_LINK_MODE_ATTR(40000);
-		CHECK_LINK_MODE_ATTR(50000);
-		CHECK_LINK_MODE_ATTR(100000);
-	}
+	scoped_guard(mutex, &trigger_data->lock)
+		for_each_set_bit(mode, supported_link_modes, __ETHTOOL_LINK_MODE_MASK_NBITS) {
+			struct ethtool_link_ksettings link_ksettings;
+
+			ethtool_params_from_link_mode(&link_ksettings, mode);
+
+			CHECK_LINK_MODE_ATTR(10);
+			CHECK_LINK_MODE_ATTR(100);
+			CHECK_LINK_MODE_ATTR(1000);
+			CHECK_LINK_MODE_ATTR(2500);
+			CHECK_LINK_MODE_ATTR(5000);
+			CHECK_LINK_MODE_ATTR(10000);
+			CHECK_LINK_MODE_ATTR(25000);
+			CHECK_LINK_MODE_ATTR(40000);
+			CHECK_LINK_MODE_ATTR(50000);
+			CHECK_LINK_MODE_ATTR(100000);
+		}
 
 	return 0;
 }
@@ -620,7 +624,6 @@ static const struct attribute_group netdev_trig_attrs_group = {
 
 static const struct attribute_group *netdev_trig_groups[] = {
 	&netdev_trig_attrs_group,
-	&netdev_trig_link_speed_attrs_group,
 	NULL,
 };
 
@@ -668,10 +671,6 @@ static int netdev_trig_notify(struct notifier_block *nb,
 		fallthrough;
 	case NETDEV_CHANGE:
 		get_device_state(trigger_data);
-		/* Refresh link_speed visibility */
-		if (evt == NETDEV_CHANGE)
-			sysfs_update_group(&led_cdev->dev->kobj,
-					   &netdev_trig_link_speed_attrs_group);
 		break;
 	}
 
@@ -679,6 +678,12 @@ static int netdev_trig_notify(struct notifier_block *nb,
 
 	mutex_unlock(&trigger_data->lock);
 
+	if (evt == NETDEV_CHANGE) {
+		scoped_guard(mutex, &trigger_data->attr_lock)
+			sysfs_update_group(&led_cdev->dev->kobj,
+					   &netdev_trig_link_speed_attrs_group);
+	}
+
 	return NOTIFY_DONE;
 }
 
@@ -759,6 +764,7 @@ static int netdev_trig_activate(struct led_classdev *led_cdev)
 		return -ENOMEM;
 
 	mutex_init(&trigger_data->lock);
+	mutex_init(&trigger_data->attr_lock);
 
 	trigger_data->notifier.notifier_call = netdev_trig_notify;
 	trigger_data->notifier.priority = 10;
@@ -794,12 +800,23 @@ static int netdev_trig_activate(struct led_classdev *led_cdev)
 
 	led_set_trigger_data(led_cdev, trigger_data);
 
+	rc = sysfs_create_group(&led_cdev->dev->kobj,
+				&netdev_trig_link_speed_attrs_group);
+	if (rc)
+		goto err_free;
+
 	rc = register_netdevice_notifier(&trigger_data->notifier);
-	if (rc) {
-		dev_put(trigger_data->net_dev);
-		kfree(trigger_data);
-	}
+	if (rc)
+		goto err_remove_group;
+
+	return 0;
 
+err_remove_group:
+	sysfs_remove_group(&led_cdev->dev->kobj,
+			   &netdev_trig_link_speed_attrs_group);
+err_free:
+	dev_put(trigger_data->net_dev);
+	kfree(trigger_data);
 	return rc;
 }
 
@@ -809,6 +826,9 @@ static void netdev_trig_deactivate(struct led_classdev *led_cdev)
 
 	unregister_netdevice_notifier(&trigger_data->notifier);
 
+	sysfs_remove_group(&led_cdev->dev->kobj,
+			   &netdev_trig_link_speed_attrs_group);
+
 	cancel_delayed_work_sync(&trigger_data->work);
 
 	dev_put(trigger_data->net_dev);
-- 
2.56.0

Re: [PATCH v7 2/3] leds: trigger: netdev: Fix sysfs_update_group() races

[sashiko-bot]

> From: Alexander Sverdlin <alexander.sverdlin@siemens.com>
> 
> The link_speed attribute group was listed in netdev_led_trigger.groups,
> so the LED core creates and destroys it via device_add_groups() /
> device_remove_groups() in led_trigger_set() (under trigger_lock), while
> the trigger also refreshes it with sysfs_update_group() from
> netdev_trig_notify() and device_name writes. With no shared lock this was
> observed as a sysfs splat when the trigger is re-armed during PHY link-up:
> 
>   sysfs: cannot create duplicate filename '...green:lan/link_10'
> 
>     CPU 0 (led_trigger_set)        CPU 1 (linkwatch workqueue)
>     -----------------------        ---------------------------
>     activate():
>       register_netdevice_notifier()
> [ ... ]
> 
> Cc: stable@vger.kernel.org
> Fixes: 06cdca014eca ("leds: trigger: netdev: Display only supported link speed attribute")
> Acked-by: Lee Jones <lee@kernel.org>
> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>

Sashiko has reviewed this patch and found no issues.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261113201936.2645736-1-alexander.sverdlin@siemens.com?part=2

[PATCH v7 3/3] leds: trigger: netdev: Report invalid interval to user space

[A. Sverdlin]

From: Alexander Sverdlin <alexander.sverdlin@siemens.com>

interval_store() silently accepts out-of-range values: a write outside
the [5, 10000] ms bounds returns the full count as if it succeeded, yet
the interval is left unchanged.

Reject out-of-range values with -EINVAL instead.

Cc: stable@vger.kernel.org
Fixes: 06f502f57d0d ("leds: trigger: Introduce a NETDEV trigger")
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>
---
Changelog:
v7:
- rebased onto for-leds-next as of 687615faae92
v6:
- patch introduced

 drivers/leds/trigger/ledtrig-netdev.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/leds/trigger/ledtrig-netdev.c b/drivers/leds/trigger/ledtrig-netdev.c
index 601c4d9e0198a..870b374fd9c48 100644
--- a/drivers/leds/trigger/ledtrig-netdev.c
+++ b/drivers/leds/trigger/ledtrig-netdev.c
@@ -509,6 +509,10 @@ static ssize_t interval_store(struct device *dev,
 	if (ret)
 		return ret;
 
+	/* impose some basic bounds on the timer interval */
+	if (value < 5 || value > 10000)
+		return -EINVAL;
+
 	mutex_lock(&trigger_data->lock);
 
 	if (trigger_data->hw_control) {
@@ -516,13 +520,10 @@ static ssize_t interval_store(struct device *dev,
 		return -EINVAL;
 	}
 
-	/* impose some basic bounds on the timer interval */
-	if (value >= 5 && value <= 10000) {
-		cancel_delayed_work_sync(&trigger_data->work);
+	cancel_delayed_work_sync(&trigger_data->work);
 
-		atomic_set(&trigger_data->interval, msecs_to_jiffies(value));
-		set_baseline_state(trigger_data);	/* resets timer */
-	}
+	atomic_set(&trigger_data->interval, msecs_to_jiffies(value));
+	set_baseline_state(trigger_data);	/* resets timer */
 
 	mutex_unlock(&trigger_data->lock);
 
-- 
2.56.0

Re: [PATCH v7 3/3] leds: trigger: netdev: Report invalid interval to user space

[sashiko-bot]

> From: Alexander Sverdlin <alexander.sverdlin@siemens.com>
> 
> interval_store() silently accepts out-of-range values: a write outside
> the [5, 10000] ms bounds returns the full count as if it succeeded, yet
> the interval is left unchanged.
> 
> Reject out-of-range values with -EINVAL instead.
> 
> Cc: stable@vger.kernel.org
> Fixes: 06f502f57d0d ("leds: trigger: Introduce a NETDEV trigger")
> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@siemens.com>

Sashiko has reviewed this patch and found no issues.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261113201936.2645736-1-alexander.sverdlin@siemens.com?part=3