On Mon, Jul 22, 2019 at 12:03 PM Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote: > > On Mon, Jul 15, 2019 at 3:46 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > > > On Mon, Jul 15, 2019 at 03:33:11PM +0200, Dmitry Vyukov wrote: > > > On Mon, Jul 15, 2019 at 3:29 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > > > > > > > On Sun, Jul 14, 2019 at 11:49:15AM -0700, Paul E. McKenney wrote: > > > > > On Sun, Jul 14, 2019 at 05:48:00PM +0300, Dmitry Vyukov wrote: > > > > > > 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. > > > > Right, well, that's part of the problem. I think Paul just did the > > reverse math and figured that 95% of X must not be larger than my > > watchdog timeout and landed on 14 seconds. > > > > I'm thinking 4 seconds (or rather 4.294967296) would be a very nice > > number. > > > > > 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? > > > > I suppose we could do that, something like: > > sysctl_deadline_period_{min,max}. I'll have to dig back a bit on where > > we last talked about that and what the problems where. > > > > For one, setting the min is a lot harder, but I suppose we can start at > > TICK_NSEC or something. > > > Now syzkaller will drop CAP_SYS_NICE for the test process: > https://github.com/google/syzkaller/commit/f3ad68446455acbe562e0057931e6256b8b991e8 > I will close this bug report as invalid once the change reaches all > syzbot instances, if nobody plans any other on this bug. #syz invalid