From: Wojtek Wasko Date: Mon, 3 Mar 2025 16:13:44 +0000 (+0200) Subject: ptp: Add PHC file mode checks. Allow RO adjtime() without FMODE_WRITE. X-Git-Tag: io_uring-6.15-20250403~82^2~170^2~1 X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=b4e53b15c04e3852949003752f48f7a14ae39e86;p=linux-2.6-block.git ptp: Add PHC file mode checks. Allow RO adjtime() without FMODE_WRITE. 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]. Additionally, POSIX layer requires WRITE permission even for readonly adjtime() calls which are used in PTP layer to return current frequency offset applied to the PHC. 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. Only require WRITE access for dynamic clocks adjtime() if any flags are set in the modes field. [1] https://lists.nwtime.org/sympa/arc/linuxptp-users/2024-01/msg00036.html Changes in v4: - Require FMODE_WRITE in ajtime() only for calls modifying the clock in any way. Acked-by: Richard Cochran Reviewed-by: Vadim Fedorenko Signed-off-by: Wojtek Wasko Reviewed-by: Thomas Gleixner Signed-off-by: David S. Miller --- diff --git a/drivers/ptp/ptp_chardev.c b/drivers/ptp/ptp_chardev.c index bf6468c56419..4380e6ddb849 100644 --- a/drivers/ptp/ptp_chardev.c +++ b/drivers/ptp/ptp_chardev.c @@ -205,6 +205,10 @@ long ptp_ioctl(struct posix_clock_context *pccontext, unsigned int cmd, case PTP_EXTTS_REQUEST: case PTP_EXTTS_REQUEST2: + if ((pccontext->fp->f_mode & FMODE_WRITE) == 0) { + err = -EACCES; + break; + } memset(&req, 0, sizeof(req)); if (copy_from_user(&req.extts, (void __user *)arg, @@ -246,6 +250,10 @@ long ptp_ioctl(struct posix_clock_context *pccontext, unsigned int cmd, case PTP_PEROUT_REQUEST: case PTP_PEROUT_REQUEST2: + if ((pccontext->fp->f_mode & FMODE_WRITE) == 0) { + err = -EACCES; + break; + } memset(&req, 0, sizeof(req)); if (copy_from_user(&req.perout, (void __user *)arg, @@ -314,6 +322,10 @@ long ptp_ioctl(struct posix_clock_context *pccontext, unsigned int cmd, case PTP_ENABLE_PPS: case PTP_ENABLE_PPS2: + if ((pccontext->fp->f_mode & FMODE_WRITE) == 0) { + err = -EACCES; + break; + } memset(&req, 0, sizeof(req)); if (!capable(CAP_SYS_TIME)) @@ -456,6 +468,10 @@ long ptp_ioctl(struct posix_clock_context *pccontext, unsigned int cmd, case PTP_PIN_SETFUNC: case PTP_PIN_SETFUNC2: + if ((pccontext->fp->f_mode & FMODE_WRITE) == 0) { + err = -EACCES; + break; + } if (copy_from_user(&pd, (void __user *)arg, sizeof(pd))) { err = -EFAULT; break; diff --git a/kernel/time/posix-clock.c b/kernel/time/posix-clock.c index 4e114e34a6e0..fe963384d5c2 100644 --- a/kernel/time/posix-clock.c +++ b/kernel/time/posix-clock.c @@ -252,7 +252,7 @@ static int pc_clock_adjtime(clockid_t id, struct __kernel_timex *tx) if (err) return err; - if ((cd.fp->f_mode & FMODE_WRITE) == 0) { + if (tx->modes && (cd.fp->f_mode & FMODE_WRITE) == 0) { err = -EACCES; goto out; }