Re: [PATCH net-next] ptp: Add file permission checks on PHC

[Vadim Fedorenko <vadim.fedorenko@linux.dev>]

On 06/02/2025 11:03, 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].
> 
> This patch adds permission checks for functions that modify the state of
> a PTP device. POSIX clock operations (settime, adjtime) continue to be
> checked 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.
> 
> [1] https://lists.nwtime.org/sympa/arc/linuxptp-users/2024-01/msg00036.html
> 
> Signed-off-by: Wojtek Wasko <wwasko@nvidia.com>
> ---
>   drivers/ptp/ptp_chardev.c             | 52 ++++++++++++++++++++-------
>   drivers/ptp/ptp_private.h             |  5 +++
>   tools/testing/selftests/ptp/testptp.c | 37 +++++++++++--------
>   3 files changed, 67 insertions(+), 27 deletions(-)

Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>