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. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
