On Mon, Oct 15, 2018 at 2:45 PM, Jan Kara <jack@xxxxxxx> wrote: > Hi Dmirty! > > On Mon 15-10-18 14:29:14, Dmitry Vyukov wrote: >> On Mon, Oct 15, 2018 at 2:15 PM, Jan Kara <jack@xxxxxxx> wrote: >> > Hello, >> > >> > On Mon 15-10-18 04:32:02, syzbot wrote: >> >> syzbot found the following crash on: >> >> >> >> HEAD commit: 90ad18418c2d Merge git://git.kernel.org/pub/scm/linux/kern.. >> >> git tree: upstream >> >> console output: https://syzkaller.appspot.com/x/log.txt?x=17f1776e400000 >> >> kernel config: https://syzkaller.appspot.com/x/.config?x=88e9a8a39dc0be2d >> >> dashboard link: https://syzkaller.appspot.com/bug?extid=29143581b0ded3213e99 >> >> compiler: gcc (GCC) 8.0.1 20180413 (experimental) >> >> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=123459d6400000 >> >> >> >> IMPORTANT: if you fix the bug, please add the following tag to the commit: >> >> Reported-by: syzbot+29143581b0ded3213e99@xxxxxxxxxxxxxxxxxxxxxxxxx >> > >> > Syzbot has apparently generated fanotify watch for FAN_OPEN_PERM event and >> > then the process got stuck waiting for userspace to respond to that event - >> > which never happened. So everything works as designed here - the process >> > placing FAN_OPEN_PERM mark is responsible for replying to the generated >> > events as all opens hang waiting for responses. That's why the >> > functionality is behind CAP_SYS_ADMIN after all... Could we fix syzbot to >> > actually generate replies for these events? >> >> Is there a reliable way to kill such processes? >> Or admins are never supposed to kill any root processes and have not >> bugs whatsoever? :) > > Currently the wait is not killable but yes, we want to make it killable > exactly because of userspace bugs :). But it is non-trivial because > currently the waker has also other responsibilities and all that stuff has > to be cleaned up when handling killed wait. Konstantin Khlebnikov was > working on that so I might need to prod him. > >> syzkaller probably capable of generating replies in some cases, but >> unfortunately it can't work this way. It's practically not possible to >> ensure that it will always generate a proper reply and it will be >> actually delivered and the process won't be killed in the middle, or >> another thread won't crash or call exit_group concurrently, etc. The >> thing either needs to be reliable, work without any but's and be >> reliably killable, or it's not suitable for stress testing. >> If there is no reliable way to kill it, I think we need to disable >> FAN_OPEN_PERM entirely. > > Understood. Then just disable FAN_OPEN_PERM & FAN_ACCESS_PERM for now. Disabled FAN_OPEN_PERM & FAN_ACCESS_PERM for now: https://github.com/google/syzkaller/commit/6ce17935cb99fa11aaa2f2d1889261da6b298013 #syz invalid
