Re: [PATCH net-next v3 2/3] ptp: Add file permission checks on PHCs

[Thomas Gleixner <tglx@linutronix.de>]

On Mon, Feb 17 2025 at 11:50, Wojtek Wasko wrote:

> Many devices implement highly accurate clocks, which the kernel manages
> as PTP Hardware Clocks (PHCs). Userspace applications rely on these
> clocks to timestamp events, trace workload execution, correlate
> timescales across devices, and keep various clocks in sync.
>
> The kernel’s current implementation of PTP clocks does not enforce file
> permissions checks for most device operations except for POSIX clock
> operations, where file mode is verified in the POSIX layer before
> forwarding the call to the PTP subsystem. Consequently, it is common
> practice to not give unprivileged userspace applications any access to
> PTP clocks whatsoever by giving the PTP chardevs 600 permissions. An
> example of users running into this limitation is documented in [1].
>
> Add permission checks for functions that modify the state of a PTP
> device. Continue enforcing permission checks for POSIX clock operations
> (settime, adjtime) in the POSIX layer. One limitation remains: querying
> the adjusted frequency of a PTP device (using adjtime() with an empty
> modes field) is not supported for chardevs opened without WRITE
> permissions, as the POSIX layer mandates WRITE access for any adjtime
> operation.

That's a fixable problem, no?