[patch 0/6] posix-cpu-timers: Fallout fixes and permission tightening

Thomas Gleixner
2019-09-05T12:12:27Z

Sysbot triggered an issue in the posix timer rework which was trivial to
fix, but after running another test case I discovered that the rework broke
the permission checks subtly. That's also a straightforward fix.

Though when staring at it I discovered that the permission checks for
process clocks and process timers are completely bonkers. The only
requirement is that the target PID is a group leader. Which means that any
process can read the clocks and attach timers to any other process without
priviledge restrictions.

That's just wrong because the clocks and timers can be used to observe
behaviour and both reading the clocks and arming timers adds overhead and
influences runtime performance of the target process.

The last 4 patches deal with that and introduce ptrace based permission
checks and also make the behaviour consistent between thread and process
timers/clocks.

Thanks,

tglx
---
include/linux/posix-timers.h | 9 +---
kernel/time/posix-cpu-timers.c | 78 ++++++++++++++++++++++++++++++++++-------
2 files changed, 69 insertions(+), 18 deletions(-)