Re: WARNING in tracepoint_probe_register_prio

[Steven Rostedt]

On Sun, 29 Oct 2017 14:24:01 -0700
syzbot <bot+2acf619eef45c8f8b322a24d8e528eccbe6319bc@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

> syzkaller has found reproducer for the following crash on  
> 36ef71cae353f88fd6e095e2aaa3e5953af1685d

So this fuzzer triggers this.

> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached
> Raw console output is attached.
> C reproducer is attached
> syzkaller reproducer is attached. See https://goo.gl/kgGztJ
> for information about syzkaller reproducers
> 
> 
> WARNING: CPU: 0 PID: 2995 at kernel/tracepoint.c:210 tracepoint_add_func  
> kernel/tracepoint.c:210 [inline]

Which is this:

	old = func_add(&tp_funcs, func, prio);
	if (IS_ERR(old)) {
		WARN_ON_ONCE(1);
		return PTR_ERR(old);
	}

Which means that func_add() returned a warning.

The possible warnings are:

	if (WARN_ON(!tp_func->func))
		return ERR_PTR(-EINVAL);

			if (old[nr_probes].func == tp_func->func &&
			    old[nr_probes].data == tp_func->data)
				return ERR_PTR(-EEXIST);

	new = allocate_probes(nr_probes + 2);
	if (new == NULL)
		return ERR_PTR(-ENOMEM);

Which means that either the tp_func->func didn't have a function. I
doubt that from the back trace, it is just the registering of the
tracepoints which should always have func set.

I doubt we ran out of memory here. Possible, but unlikely (this was
reproduced twice with the same path).

Which leaves us with a tracepoint that was registered twice.

There's nothing in register_trace_*() that protects it. The blktrace
code needs to have some protection to know if it registered the
tracepoints once, otherwise this will trigger.


> WARNING: CPU: 0 PID: 2995 at kernel/tracepoint.c:210  
> tracepoint_probe_register_prio+0x397/0x9a0 kernel/tracepoint.c:283
> Kernel panic - not syncing: panic_on_warn set ...

It panics because "panic_on_warn" is set and we just did a warning.

> 
> CPU: 0 PID: 2995 Comm: syzkaller857118 Not tainted  
> 4.14.0-rc5-next-20171018+ #36
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
> Google 01/01/2011
> Call Trace:
>   __dump_stack lib/dump_stack.c:16 [inline]
>   dump_stack+0x194/0x257 lib/dump_stack.c:52
>   panic+0x1e4/0x41c kernel/panic.c:183
>   __warn+0x1c4/0x1e0 kernel/panic.c:546
>   report_bug+0x211/0x2d0 lib/bug.c:183
>   fixup_bug+0x40/0x90 arch/x86/kernel/traps.c:177
>   do_trap_no_signal arch/x86/kernel/traps.c:211 [inline]
>   do_trap+0x260/0x390 arch/x86/kernel/traps.c:260
>   do_error_trap+0x120/0x390 arch/x86/kernel/traps.c:297
>   do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:310
>   invalid_op+0x18/0x20 arch/x86/entry/entry_64.S:905
> RIP: 0010:tracepoint_add_func kernel/tracepoint.c:210 [inline]
> RIP: 0010:tracepoint_probe_register_prio+0x397/0x9a0 kernel/tracepoint.c:283
> RSP: 0018:ffff8801d1d1f6c0 EFLAGS: 00010293
> RAX: ffff8801d22e8540 RBX: 00000000ffffffef RCX: ffffffff81710f07
> RDX: 0000000000000000 RSI: ffffffff85b679c0 RDI: ffff8801d5f19818
> RBP: ffff8801d1d1f7c8 R08: ffffffff81710c10 R09: 0000000000000004
> R10: ffff8801d1d1f6b0 R11: 0000000000000003 R12: ffffffff817597f0
> R13: 0000000000000000 R14: 00000000ffffffff R15: ffff8801d1d1f7a0
>   tracepoint_probe_register+0x2a/0x40 kernel/tracepoint.c:304
>   register_trace_block_rq_insert include/trace/events/block.h:191 [inline]
>   blk_register_tracepoints+0x1e/0x2f0 kernel/trace/blktrace.c:1043
>   do_blk_trace_setup+0xa10/0xcf0 kernel/trace/blktrace.c:542
>   blk_trace_setup+0xbd/0x180 kernel/trace/blktrace.c:564

I'm guessing the blk_trace_setup should have a mutex or something to
protect this. Atomic counters is not enough.


	CPU0					CPU1
	----					----
 if (atomic_inc_return(&blk_probes_ref) == 1)
	blk_register_tracepoints();

 if (atomic_dec_and_test(&blk_probes_ref))

				if (atomic_inc_return(&blk_probes_ref) == 1)
					blk_register_tracepoints();

	blk_unregister_tracepoints();

Would cause this to trigger.

-- Steve


>   sg_ioctl+0xc71/0x2d90 drivers/scsi/sg.c:1089
>   vfs_ioctl fs/ioctl.c:45 [inline]
>   do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:685
>   SYSC_ioctl fs/ioctl.c:700 [inline]
>   SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
>   entry_SYSCALL_64_fastpath+0x1f/0xbe
> RIP: 0033:0x444339
> RSP: 002b:00007ffe05bb5b18 EFLAGS: 00000206 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00000000006d66c0 RCX: 0000000000444339
> RDX: 000000002084cf90 RSI: 00000000c0481273 RDI: 0000000000000009
> RBP: 0000000000000082 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000206 R12: ffffffffffffffff
> R13: 00000000c0481273 R14: 0000000000000000 R15: 0000000000000000
> Dumping ftrace buffer:
>     (ftrace buffer empty)
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
>