On Mon, Jul 15, 2019 at 3:29 PM Peter Zijlstra [off-list ref] wrote:

On Sun, Jul 14, 2019 at 11:49:15AM -0700, Paul E. McKenney wrote:

quoted

On Sun, Jul 14, 2019 at 05:48:00PM +0300, Dmitry Vyukov wrote:

quoted

But short term I don't see any other solution than stop testing
sched_setattr because it does not check arguments enough to prevent
system misbehavior. Which is a pity because syzkaller has found some
bad misconfigurations that were oversight on checking side.
Any other suggestions?

Keep the times down to a few seconds?  Of course, that might also
fail to find interesting bugs.

Right, if syzcaller can put a limit on the period/deadline parameters
(and make sure to not write "-1" to
/proc/sys/kernel/sched_rt_runtime_us) then per the in-kernel
access-control should not allow these things to happen.

Since we are racing with emails, could you suggest a 100% safe
parameters? Because I only hear people saying "safe", "sane",
"well-behaving" :)
If we move the check to user-space, it does not mean that we can get
away without actually defining what that means.

Now thinking of this, if we come up with some simple criteria, could
we have something like a sysctl that would allow only really "safe"
parameters?