timekeeping: Require permission to set auxiliary clocks

The generic clock_settime() entry point delegates permission checks to
each clock-specific callback. aux_clock_set() does not perform one. Once
an administrator enables an auxiliary clock, any local process can
therefore change the global clock offset.

A test process running as UID and GID 65534 with no effective, permitted,
inheritable, or ambient capabilities set CLOCK_AUX0 successfully, and a
separate process observed the new value. The same process was denied by
clock_adjtime(). An AppArmor profile denying sys_time also blocked
CLOCK_REALTIME changes but did not see the auxiliary clock operation.

Call security_settime64() before mutating the auxiliary timekeeper. This
matches CLOCK_REALTIME's permission model, enforces initial-user-namespace
CAP_SYS_TIME, and gives LSMs the settime hook while preserving authorized
clock changes.

Fixes: 60ecc26ec5af ("timekeeping: Provide time setter for auxiliary clocks")
Signed-off-by: Daehyeon Ko <4ncienth@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: shaos <shawnq1@163.com>
Acked-by: John Stultz <jstultz@google.com>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20261019080324.4147815-1-4ncienth@gmail.com

0 files changed, 0 insertions, 0 deletions