On Tue, Mar 31, 2020 at 2:50 PM Daniel Vetter daniel@ffwll.ch wrote:
On Tue, Mar 31, 2020 at 2:18 PM Bartlomiej Zolnierkiewicz b.zolnierkie@samsung.com wrote:
On 3/31/20 12:18 PM, Dmitry Vyukov wrote:
On Tue, Mar 31, 2020 at 11:57 AM Peter Zijlstra peterz@infradead.org wrote:
On Mon, Mar 30, 2020 at 10:01:12PM -0700, syzbot wrote:
Hello,
syzbot found the following crash on:
HEAD commit: 9420e8ad Merge tag 'for-linus' of git://git.kernel.org/pub.. git tree: upstream console output: https://protect2.fireeye.com/url?k=0756a78d-5a9a6c49-07572cc2-0cc47a314e9a-e... kernel config: https://protect2.fireeye.com/url?k=43211072-1eeddbb6-43209b3d-0cc47a314e9a-3... dashboard link: https://protect2.fireeye.com/url?k=bf7a6153-e2b6aa97-bf7bea1c-0cc47a314e9a-c... compiler: gcc (GCC) 9.0.0 20181231 (experimental)
Unfortunately, I don't have any reproducer for this crash yet.
IMPORTANT: if you fix the bug, please add the following tag to the commit: Reported-by: syzbot+e84d7ebd1361da13c356@syzkaller.appspotmail.com
INFO: trying to register non-static key. the code is fine but needs lockdep annotation. turning off the locking correctness validator. CPU: 1 PID: 1014 Comm: syz-executor.0 Not tainted 5.6.0-rc7-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace:
<IRQ> __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x188/0x20d lib/dump_stack.c:118 assign_lock_key kernel/locking/lockdep.c:880 [inline] register_lock_class+0x14c4/0x1540 kernel/locking/lockdep.c:1189 __lock_acquire+0xfc/0x3ca0 kernel/locking/lockdep.c:3836 lock_acquire+0x197/0x420 kernel/locking/lockdep.c:4484 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline] _raw_spin_lock_irqsave+0x8c/0xbf kernel/locking/spinlock.c:159 try_to_wake_up+0x9f/0x17c0 kernel/sched/core.c:2547
That's p->pi_lock, which gets initialized in rt_mutex_init_task() in copy_process(). This should be impossible. Very odd.
The stack mentions fbdev, which is a red flag at the moment. There are a dozen of bad bugs in fbdev and around. Just few days ago Andy pointed to another "impossible" crash "general protection fault in do_syscall_64" which is related to dri: https://protect2.fireeye.com/url?k=0cb8ad06-517466c2-0cb92649-0cc47a314e9a-a... https://protect2.fireeye.com/url?k=614292e3-3c8e5927-614319ac-0cc47a314e9a-a...
There are probably more random manifestations of these bugs already, and I guess we will be getting more.
+fbdev maintainers
Thank you for the report.
fbdev is in the maintenance mode and no new features or drivers are being added so syzbot reports are not for a new bugs (regressions) and are not a priority (at least to me).
Yup same here, I've seen a pile of syzbot reports for fbdev (and also vt, or combinations of them since fbdev is linked to vt through fbcon) fly by. But I really don't have to deal with these, my recommendation to anyone who cares about security are:
- Don't enable vt
- Don't enable fbdev
1. How do we deliver this message to relevant people?
Because:
$ grep FBDEV syzkaller/dashboard/config/upstream-kasan.config CONFIG_DRM_FBDEV_EMULATION=y CONFIG_DRM_FBDEV_OVERALLOC=100 # CONFIG_DRM_FBDEV_LEAK_PHYS_SMEM is not set CONFIG_XEN_FBDEV_FRONTEND=y
and my current work machine:
$ grep FBDEV /boot/config-5.2.17-1-amd64 CONFIG_DRM_FBDEV_EMULATION=y CONFIG_DRM_FBDEV_OVERALLOC=100 # CONFIG_DRM_FBDEV_LEAK_PHYS_SMEM is not set CONFIG_XEN_FBDEV_FRONTEND=y
2. What do we do with fbdev testing on syzbot? Is there a way to disable all of the unsupported stuff? But if we disable it, we don't find any regressions as well. And in the end that's what is in the mainline kernel and is still enabled in distros (at least in the 2 real configs I can grep now).
All that code has been developed long ago, in a much more innocent time. If someone wants to fix this you'd not just need to fix all the syzbot stuff, but also ramp up a full testsuite for all the ioctl, and all the corner-cases. Plus also fix some of the horrendous locking in there, probably.
Multi-year effort, easily.
Regressions I'll obviously try to handle, but none of these are. It's just syzbot has become smarter at hitting bugs in fbdev and vt subsystems (or maybe the hw the virtual machines emulate has become more varied, some of the reports are for fun stuff like vgacon ...).
Cheers, Daniel
I have only resources to review/merge pending fbdev patches from time to time so any help in fixing these syzbot reports is welcomed (there have been a few fbdev related syzbot reports recently).
Also please note that fbdev is maintained through drm-misc tree so patches can also be handled by other drm-misc maintainers in case I'm not available / busy with other things.
Best regards,
Bartlomiej Zolnierkiewicz Samsung R&D Institute Poland Samsung Electronics
wake_up_worker kernel/workqueue.c:836 [inline] insert_work+0x2ad/0x3a0 kernel/workqueue.c:1337 __queue_work+0x50d/0x1280 kernel/workqueue.c:1488 call_timer_fn+0x195/0x760 kernel/time/timer.c:1404 expire_timers kernel/time/timer.c:1444 [inline] __run_timers kernel/time/timer.c:1773 [inline] __run_timers kernel/time/timer.c:1740 [inline] run_timer_softirq+0x412/0x1600 kernel/time/timer.c:1786 __do_softirq+0x26c/0x99d kernel/softirq.c:292 invoke_softirq kernel/softirq.c:373 [inline] irq_exit+0x192/0x1d0 kernel/softirq.c:413 exiting_irq arch/x86/include/asm/apic.h:546 [inline] smp_apic_timer_interrupt+0x19e/0x600 arch/x86/kernel/apic/apic.c:1146 apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:829
</IRQ>
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-- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch