netdev - [PATCH] ptp: Add sysfs attribute to show clock is safe to open RO

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Message-ID: <20250514143622.4104588-1-wwasko@nvidia.com>
Date: Wed, 14 May 2025 17:36:21 +0300
From: Wojtek Wasko <wwasko@...dia.com>
To: richardcochran@...il.com,
	vadim.fedorenko@...ux.dev
Cc: netdev@...r.kernel.org,
	Wojtek Wasko <wwasko@...dia.com>
Subject: [PATCH] ptp: Add sysfs attribute to show clock is safe to open RO

Recent patches introduced in 6.15 implement permissions checks for PTP
clocks. Prior to those, a process with readonly access could modify the
state of PTP devices, in particular the generation and consumption of
PPS signals.

Userspace (e.g. udev) managing the ownership and permissions of device
nodes lacks information as to whether kernel implements the necessary
security checks and whether it is safe to expose readonly access to
PTP devices to unprivileged users. Kernel version checks are cumbersome
and prone to failure, especially if backports are considered [1].

Add a readonly sysfs attribute to PTP clocks, "ro_safe", backed by a
static string.

[1] https://github.com/systemd/systemd/pull/37302#issuecomment-2850510329
---
 drivers/ptp/ptp_sysfs.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/ptp/ptp_sysfs.c b/drivers/ptp/ptp_sysfs.c
index 6b1b8f57cd95..763fc54cf267 100644
--- a/drivers/ptp/ptp_sysfs.c
+++ b/drivers/ptp/ptp_sysfs.c
@@ -28,6 +28,8 @@ static ssize_t max_phase_adjustment_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(max_phase_adjustment);

+static DEVICE_STRING_ATTR_RO(ro_safe, 0444, "1\n");
+
 #define PTP_SHOW_INT(name, var)						\
 static ssize_t var##_show(struct device *dev,				\
 			   struct device_attribute *attr, char *page)	\
@@ -320,6 +322,7 @@ static DEVICE_ATTR_RW(max_vclocks);

 static struct attribute *ptp_attrs[] = {
 	&dev_attr_clock_name.attr,
+	&dev_attr_ro_safe.attr.attr,

 	&dev_attr_max_adjustment.attr,
 	&dev_attr_max_phase_adjustment.attr,
-- 
2.43.5