Re: mm: GPF in __insert_vmap_area

[Kees Cook]

On Tue, Sep 6, 2016 at 4:11 PM, Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote:
> On 09/06/2016 11:03 PM, Kees Cook wrote:
>>
>> On Sat, Sep 3, 2016 at 8:15 AM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>>>
>>> Hello,
>>>
>>> While running syzkaller fuzzer I've got the following GPF:
>>>
>>> general protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN
>>> Dumping ftrace buffer:
>>>     (ftrace buffer empty)
>>> Modules linked in:
>>> CPU: 2 PID: 4268 Comm: syz-executor Not tainted 4.8.0-rc3-next-20160825+
>>> #8
>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs
>>> 01/01/2011
>>> task: ffff88006a6527c0 task.stack: ffff880052630000
>>> RIP: 0010:[<ffffffff82e1ccd6>]  [<ffffffff82e1ccd6>]
>>> __list_add_valid+0x26/0xd0 lib/list_debug.c:23
>>> RSP: 0018:ffff880052637a18  EFLAGS: 00010202
>>> RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffc90001c87000
>>> RDX: 0000000000000001 RSI: ffff88001344cdb0 RDI: 0000000000000008
>>> RBP: ffff880052637a30 R08: 0000000000000001 R09: 0000000000000000
>>> R10: 0000000000000000 R11: ffffffff8a5deee0 R12: ffff88006cc47230
>>> R13: ffff88001344cdb0 R14: ffff88006cc47230 R15: 0000000000000000
>>> FS:  00007fbacc97e700(0000) GS:ffff88006d200000(0000)
>>> knlGS:0000000000000000
>>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> CR2: 0000000020de7000 CR3: 000000003c4d2000 CR4: 00000000000006e0
>>> DR0: 000000000000001e DR1: 000000000000001e DR2: 0000000000000000
>>> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
>>> Stack:
>>>   ffff88006cc47200 ffff88001344cd98 ffff88006cc47200 ffff880052637a78
>>>   ffffffff817bc6d1 ffff88006cc47208 ffffed000d988e41 ffff88006cc47208
>>>   ffff88006cc3e680 ffffc900035b7000 ffffc900035a7000 ffff88006cc47200
>>> Call Trace:
>>>   [<     inline     >] __list_add_rcu include/linux/rculist.h:51
>>>   [<     inline     >] list_add_rcu include/linux/rculist.h:78
>>>   [<ffffffff817bc6d1>] __insert_vmap_area+0x1c1/0x3c0 mm/vmalloc.c:340
>>>   [<ffffffff817bf544>] alloc_vmap_area+0x614/0x890 mm/vmalloc.c:458
>>>   [<ffffffff817bf8a8>] __get_vm_area_node+0xe8/0x340 mm/vmalloc.c:1377
>>>   [<ffffffff817c332a>] __vmalloc_node_range+0xaa/0x6d0 mm/vmalloc.c:1687
>>>   [<     inline     >] __vmalloc_node mm/vmalloc.c:1736
>>>   [<ffffffff817c39ab>] __vmalloc+0x5b/0x70 mm/vmalloc.c:1742
>>>   [<ffffffff8166ae9c>] bpf_prog_alloc+0x3c/0x190 kernel/bpf/core.c:82
>>>   [<ffffffff85c40ba9>] bpf_prog_create_from_user+0xa9/0x2c0
>>> net/core/filter.c:1132
>>>   [<     inline     >] seccomp_prepare_filter kernel/seccomp.c:373
>>>   [<     inline     >] seccomp_prepare_user_filter kernel/seccomp.c:408
>>>   [<     inline     >] seccomp_set_mode_filter kernel/seccomp.c:737
>>>   [<ffffffff815d7687>] do_seccomp+0x317/0x1800 kernel/seccomp.c:787
>>>   [<ffffffff815d8f84>] prctl_set_seccomp+0x34/0x60 kernel/seccomp.c:830
>>>   [<     inline     >] SYSC_prctl kernel/sys.c:2157
>>>   [<ffffffff813ccf8f>] SyS_prctl+0x82f/0xc80 kernel/sys.c:2075
>>>   [<ffffffff86e10700>] entry_SYSCALL_64_fastpath+0x23/0xc1
>>> Code: 00 00 00 00 00 55 48 b8 00 00 00 00 00 fc ff df 48 89 e5 41 54
>>> 49 89 fc 48 8d 7a 08 53 48 89 d3 48 89 fa 48 83 ec 08 48 c1 ea 03 <80>
>>> 3c 02 00 75 7c 48 8b 53 08 48 39 f2 75 37 48 89 f2 48 b8 00
>>> RIP  [<ffffffff82e1ccd6>] __list_add_valid+0x26/0xd0 lib/list_debug.c:23
>>>   RSP <ffff880052637a18>
>>> ---[ end trace 983e625f02f00d9f ]---
>>> Kernel panic - not syncing: Fatal exception
>>>
>>> On commit 0f98f121e1670eaa2a2fbb675e07d6ba7f0e146f of linux-next.
>>> Unfortunately it is not reproducible.
>
>
> Can you elaborate? You hit this only once and then never again
> in this or some other, similar call-trace form, right?

That's my understanding.

>>> The crashing line is:
>>>          CHECK_DATA_CORRUPTION(next->prev != prev,
>>>
>>> It crashed on KASAN check at (%rax, %rdx), this address corresponds to
>>> next address = 0x8. So next was ~NULL.
>>
>>
>> Paul, the RCU torture tests passed with the CONFIG_DEBUG_LIST changes,
>> IIRC, yes? I'd love to rule out some kind of race condition between
>> the removal and add code for the checking.
>>
>> Daniel, IIRC there was some talk about RCU and BPF? Am I remembering
>
>
> --verbose, what talk specifically? There were some fixes longer
> time ago, but related to eBPF, not cBPF, but even there I don't
> see currently how it could be related to a va->list corruption
> triggered in __insert_vmap_area().

I meant "discussion", but digging around I think I was remembering this:

5a5abb1fa3b05dd6aa821525832644c1e7d2905f
tun, bpf: fix suspicious RCU usage in tun_{attach, detach}_filter

But that doesn't appear to relate at all. Hmm.

>> that correctly? I'm having a hard time imagining how a list add could
>> fail (maybe a race between two adds)?
>
> Or some use after free that would have corrupted that memory? I
> would think right now that the path via bpf_prog_alloc() could
> have triggered, but not necessarily caused the issue, hmm.

Yeah, I'm really baffled about this.

-Kees

-- 
Kees Cook
Nexus Security