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udev: grant read access to PTP devices for unprivileged users

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Change the default udev rule for /dev/ptp* from 0660 to 0664,
allowing unprivileged users read-only access.

NIC telemetry and hardware logs often use device timestamps that must
be correlated with host time via read-only PTP ioctls (e.g.
cross-timestamp queries). Requiring privileged access makes these
workflows unnecessarily restrictive.

Older kernels lacked proper permission checks in some PTP ioctls.
Kernel commit b4e53b15c04e3852949003752f48f7a14ae39e86 ("ptp: Add PHC
file mode checks. Allow RO adjtime() without FMODE_WRITE.") introduces
the necessary file mode validation, ensuring that read access does not
permit clock modification or configuration changes, which still require
write permissions.

This commit has been backported to all actively maintained stable
kernel branches.

Related to #31034
This commit is contained in:
Carolina Jubran
2026-02-16 11:24:53 +02:00
committed by Lennart Poettering
parent dbc83d6353
commit 1e6854e112
2 changed files with 11 additions and 1 deletions
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2
rules.d/50-udev-default.rules.in
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@@ -31,7 +31,7 @@ SUBSYSTEM=="pci|usb|platform", IMPORT{builtin}="path_id"
SUBSYSTEM=="net", IMPORT{builtin}="net_driver"
SUBSYSTEM=="ptp", GROUP="clock", MODE="0660"
SUBSYSTEM=="ptp", GROUP="clock", MODE="0664"
SUBSYSTEM=="ptp", ATTR{clock_name}=="KVM virtual PTP", SYMLINK+="ptp_kvm"
SUBSYSTEM=="ptp", ATTR{clock_name}=="hyperv", SYMLINK+="ptp_hyperv"
SUBSYSTEM=="ptp", ATTR{clock_name}=="ptp_vmw", SYMLINK+="ptp_vmware"