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Date: Fri, 17 Nov 2017 16:27:42 -0800
From: Patrick McLean <chutzpah@...too.org>
To: Kees Cook <keescook@...omium.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
 Emese Revfy <re.emese@...il.com>, Al Viro <viro@...iv.linux.org.uk>,
 Bruce Fields <bfields@...hat.com>, "Darrick J. Wong"
 <darrick.wong@...cle.com>,
 Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
 Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
 stable <stable@...r.kernel.org>,
 Thorsten Leemhuis <regressions@...mhuis.info>,
 "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Subject: Re: [nfsd4] potentially hardware breaking regression in 4.14-rc and
 4.13.11

On 2017-11-17 01:26 PM, Kees Cook wrote:
> On Fri, Nov 17, 2017 at 11:03 AM, Patrick McLean <chutzpah@...too.org> wrote:
>> On 2017-11-16 04:54 PM, Kees Cook wrote:
>>> On Mon, Nov 13, 2017 at 2:48 PM, Patrick McLean <chutzpah@...too.org> wrote:
>>>> On 2017-11-11 09:31 AM, Linus Torvalds wrote:
>>>>> Boris Lukashev points out that Patrick should probably check a newer
>>>>> version of gcc.
>>>>>
>>>>> I looked around, and in one of the emails, Patrick said:
>>>>>
>>>>>   "No changes, both the working and broken kernels were built with
>>>>>    distro-provided gcc 5.4.0 and binutils 2.28.1"
>>>>>
>>>>> and gcc-5.4.0 is certainly not very recent. It's not _ancient_, but
>>>>> it's a bug-fix release to a pretty old branch that is not exactly new.
>>>>>
>>>>> It would probably be good to check if the problems persist with gcc
>>>>> 6.x or 7.x.. I have no idea which gcc version the randstruct people
>>>>> tend to use themselves.
>>>>
>>>> I just tested it with gcc 7.2, and was able to reproduce the NULL
>>>> pointer dereference, the backtrace looks slightly different this time.
>>>>
>>>> I will also test with binutils 2.29, though I doubt that will make any
>>>> difference.
>>>>
>>>>> [   56.165181] BUG: unable to handle kernel NULL pointer dereference at 0000000000000560
>>>>> [   56.166563] IP: vfs_statfs+0x7c/0xc0
>>>>> [   56.167249] PGD 0 P4D 0
>>>>> [   56.167860] Oops: 0000 [#1] SMP
>>>>> [   56.176478] Modules linked in: ipt_MASQUERADE nf_nat_masquerade_ipv4 xt_multiport xt_addrtype iptable_mangle iptable>
>>>>> [   56.180227] CPU: 0 PID: 3985 Comm: nfsd Tainted: G           O    4.14.0-git-kratos-1 #1
>>>>> [   56.181728] Hardware name: TYAN S5510/S5510, BIOS V2.02 03/12/2013
>>>>> [   56.182729] task: ffff88040c412a00 task.stack: ffffc90002c18000
>>>>> [   56.183629] RIP: 0010:vfs_statfs+0x7c/0xc0
>>>>> [   56.184341] RSP: 0018:ffffc90002c1bb28 EFLAGS: 00010202
>>>>> [   56.185143] RAX: 0000000000000000 RBX: ffffc90002c1bbf0 RCX: 0000000000000020
>>>>> [   56.186085] RDX: 0000000000001801 RSI: 0000000000001801 RDI: 0000000000000000
>>>>> [   56.187066] RBP: ffffc90002c1bbc0 R08: ffffffffffffff00 R09: 00000000000000ff
>>>>> [   56.188268] R10: 000000000038be3a R11: ffff880408b18258 R12: 0000000000000000
>>>>> [   56.189336] R13: ffff88040c23ad00 R14: ffff88040b874000 R15: ffffc90002c1bbf0
>>>>> [   56.190444] FS:  0000000000000000(0000) GS:ffff88041fc00000(0000) knlGS:0000000000000000
>>>>> [   56.191876] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>>> [   56.192843] CR2: 0000000000000560 CR3: 0000000001e0a002 CR4: 00000000001606f0
>>>>> [   56.193898] Call Trace:
>>>>> [   56.194510]  nfsd4_encode_fattr+0x201/0x1f90
>>>>> [   56.195267]  ? generic_permission+0x12c/0x1a0
>>>>> [   56.196025]  nfsd4_encode_getattr+0x25/0x30
>>>>> [   56.196753]  nfsd4_encode_operation+0x98/0x1b0
>>>>> [   56.197526]  nfsd4_proc_compound+0x2a0/0x5e0
>>>>> [   56.198268]  nfsd_dispatch+0xe8/0x220
>>>>> [   56.198968]  svc_process_common+0x475/0x640
>>>>> [   56.199696]  ? nfsd_destroy+0x60/0x60
>>>>> [   56.200404]  svc_process+0xf2/0x1a0
>>>>> [   56.201079]  nfsd+0xe3/0x150
>>>>> [   56.201706]  kthread+0x117/0x130
>>>>> [   56.202354]  ? kthread_create_on_node+0x40/0x40
>>>>> [   56.203100]  ret_from_fork+0x25/0x30
>>>>> [   56.203774] Code: d6 89 d6 81 ce 00 04 00 00 f6 c1 08 0f 45 d6 89 d6 81 ce 00 08 00 00 f6 c1 10 0f 45 d6 89 d6 81 ce>
>>>>> [   56.206289] RIP: vfs_statfs+0x7c/0xc0 RSP: ffffc90002c1bb28
>>>>> [   56.207110] CR2: 0000000000000560
>>>>> [   56.207763] ---[ end trace d452986a80f64aaa ]---
>>>>
>>>>> On Sat, Nov 11, 2017 at 8:13 AM, Kees Cook <keescook@...omium.org> wrote:
>>>>>>
>>>>>> I'll take a closer look at this and see if I can provide something to
>>>>>> narrow it down.
>>>
>>> How reliable is this crash? The best idea I have to isolate it would
>>> be to bisect the additions of the __randomize_layout markings on
>>> various structures. I would start with the ones Al is most upset to
>>> see randomized. ;)
>>
>> It's pretty reliable, once I get a bad seed I can reproduce the crash
>> pretty quickly.
>>
>>> For the first step, I'd try a revert of
>>> 9225331b310821760f39ba55b00b8973602adbb5, which enables a large
>>> portion of struct randomization. If that doesn't change things, I can
>>> provide a series that reverts 3859a271a003aba01e45b85c9d8b355eb7bf25f9
>>> and then re-applies __randomize_layout one structure per patch, and
>>> you could bisect that?
>>
>> Sure, I can bisect that.
> 
> Okay, that should at least let us know if this is a specific struct
> that is not expecting to get randomized, or if there is some deeper
> flaw. Here's the tree, based on 4.14:
> https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/log/?h=kspp/randstruct/bisection
> 
> With commit d9e12200852d, all randomization selections are reverted. I
> would expect this to be a "good" kernel for the bisect.

I am still getting the crash at d9e12200852d, I figured I would
double-check the "good" and "bad" kernels before starting a full bisect.

I guess it must be something somewhere else? I am happy to test or
bisect more patches.

Here is the BUG message for reference:
> [   56.495987] BUG: unable to handle kernel NULL pointer dereference at 0000000000000560
> [   56.497404] IP: vfs_statfs+0x7c/0xc0
> [   56.498092] PGD 0 P4D 0 
> [   56.498716] Oops: 0000 [#1] SMP
> [   56.499366] Modules linked in: ipt_MASQUERADE nf_nat_masquerade_ipv4 xt_multiport xt_addrtype iptable_mangle iptable_raw iptable_nat nf_nat_ipv4 nf_nat gkuart(O) usbserial x86_pkg_temp_thermal tpm_tis ipmi_ssif tpm_tis_core ie31200_edac ext4 mbcache jbd2 e1000e crc32c_intel
> [   56.502653] CPU: 0 PID: 3975 Comm: nfsd Tainted: G           O    4.14.0-git-kratos-1-00061-gd893c17b3146 #3
> [   56.504071] Hardware name: TYAN S5510/S5510, BIOS V2.02 03/12/2013
> [   56.504957] task: ffff88040cba7000 task.stack: ffffc90002c08000
> [   56.505843] RIP: 0010:vfs_statfs+0x7c/0xc0
> [   56.506571] RSP: 0018:ffffc90002c0bb28 EFLAGS: 00010202
> [   56.507383] RAX: 0000000000000000 RBX: ffffc90002c0bbf0 RCX: 0000000000000020
> [   56.508354] RDX: 0000000000001000 RSI: 0000000000001000 RDI: 0000000000000000
> [   56.509545] RBP: ffffc90002c0bbc0 R08: ffffffffffffff00 R09: 00000000000000ff
> [   56.510622] R10: 000000000038be3a R11: ffff8804087563e8 R12: 0000000000000000
> [   56.511693] R13: ffff88040c68d000 R14: ffff88040c4df000 R15: ffffc90002c0bbf0
> [   56.512764] FS:  0000000000000000(0000) GS:ffff88041fc00000(0000) knlGS:0000000000000000
> [   56.514216] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   56.515199] CR2: 0000000000000560 CR3: 0000000001e0a005 CR4: 00000000001606f0
> [   56.516268] Call Trace:
> [   56.516903]  nfsd4_encode_fattr+0x201/0x1f90
> [   56.517686]  ? generic_permission+0x12c/0x1a0
> [   56.518467]  nfsd4_encode_getattr+0x25/0x30
> [   56.519220]  nfsd4_encode_operation+0x98/0x1b0
> [   56.519991]  nfsd4_proc_compound+0x2a0/0x5e0
> [   56.520758]  nfsd_dispatch+0xe8/0x220
> [   56.521476]  svc_process_common+0x475/0x640
> [   56.522221]  ? nfsd_destroy+0x60/0x60
> [   56.522923]  svc_process+0xf2/0x1a0
> [   56.523611]  nfsd+0xe3/0x150
> [   56.524241]  kthread+0x117/0x130
> [   56.524896]  ? kthread_create_on_node+0x40/0x40
> [   56.525630]  ret_from_fork+0x25/0x30
> [   56.526306] Code: d6 89 d6 81 ce 00 04 00 00 f6 c1 08 0f 45 d6 89 d6 81 ce 00 08 00 00 f6 c1 10 0f 45 d6 89 d6 81 ce 00 10 00 00 83 e1 20 0f 45 d6 <48> 8b b7 60 05 00 00 bf 10 00 00 00 83 ca 20 89 f1 83 e1 10 0f
> [   56.528885] RIP: vfs_statfs+0x7c/0xc0 RSP: ffffc90002c0bb28
> [   56.529772] CR2: 0000000000000560
> [   56.530464] ---[ end trace e6cf48f1f8c0ee4e ]---


> 
> The very end of the series (commit d893c17b3146), everything is back
> to being randomized. I would expect this to be a "bad" kernel.
> 
> Each step between those two commits adds randomization to a single
> struct (with the filesystem stuff near the front).
> 
> Here's hoping it'll be something obvious. :) Thanks for taking the
> time to debug this!

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