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

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Message-ID: <87cyfgjp54.ffs@tglx>
Date: Mon, 17 Feb 2025 21:24:23 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Wojtek Wasko <wwasko@...dia.com>, netdev@...r.kernel.org
Cc: richardcochran@...il.com, vadim.fedorenko@...ux.dev, kuba@...nel.org,
 horms@...nel.org, anna-maria@...utronix.de, frederic@...nel.org,
 pabeni@...hat.com
Subject: Re: [PATCH net-next v3 2/3] ptp: Add file permission checks on PHCs

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?