Messages in this thread | | | Date | Thu, 5 Sep 2019 16:48:30 +0200 | From | Frederic Weisbecker <> | Subject | Re: [patch 0/6] posix-cpu-timers: Fallout fixes and permission tightening |
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On Thu, Sep 05, 2019 at 02:03:39PM +0200, Thomas Gleixner wrote: > 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.
Yeah I stumbled upon that by the past and found out the explanation behind in old history: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git/commit/kernel/posix-cpu-timers.c?id=a78331f2168ef1e67b53a0f8218c70a19f0b2a4c
"This makes no constraint on who can see whose per-process clocks. This information is already available for the VIRT and PROF (i.e. utime and stime) information via /proc. I am open to suggestions on if/how security constraints on who can see whose clocks should be imposed."
I'm all for mitigating that, let's just hope that won't break some ABIs.
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