Date:   Mon, 06 Apr 2020 18:05:59 -0700
From:   syzbot <syzbot+693dc11fcb53120b5559@...kaller.appspotmail.com>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     akpm@...ux-foundation.org, bgeffon@...gle.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        peterx@...hat.com, rdunlap@...radead.org,
        syzkaller-bugs@...glegroups.com, torvalds@...ux-foundation.org
Subject: Re: Re: BUG: unable to handle kernel paging request in kernel_get_mempolicy

> On 4/6/20 5:47 PM, Peter Xu wrote:
>> On Mon, Apr 06, 2020 at 11:16:13AM -0700, syzbot wrote:
>>> Hello,
>>>
>>> syzbot found the following crash on:
>>>
>>> HEAD commit:    bef7b2a7 Merge tag 'devicetree-for-5.7' of git://git.kerne..
>>> git tree:       upstream
>>> console output: https://syzkaller.appspot.com/x/log.txt?x=13966e8fe00000
>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=91b674b8f0368e69
>>> dashboard link: https://syzkaller.appspot.com/bug?extid=693dc11fcb53120b5559
>>> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
>>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1738b02be00000
>>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17d2c76de00000
>>>
>>> The bug was bisected to:
>>>
>>> commit 4426e945df588f2878affddf88a51259200f7e29
>>> Author: Peter Xu <peterx@...hat.com>
>>> Date:   Thu Apr 2 04:08:49 2020 +0000
>>>
>>>     mm/gup: allow VM_FAULT_RETRY for multiple times
>>>
>>> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=14ac4a5de00000
>>> final crash:    https://syzkaller.appspot.com/x/report.txt?x=16ac4a5de00000
>>> console output: https://syzkaller.appspot.com/x/log.txt?x=12ac4a5de00000
>>>
>>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>>> Reported-by: syzbot+693dc11fcb53120b5559@...kaller.appspotmail.com
>>> Fixes: 4426e945df58 ("mm/gup: allow VM_FAULT_RETRY for multiple times")
>>>
>>> BUG: unable to handle page fault for address: ffffffff00000000
>>> #PF: supervisor read access in kernel mode
>>> #PF: error_code(0x0000) - not-present page
>>> PGD 987c067 P4D 987c067 PUD 0 
>>> Oops: 0000 [#1] PREEMPT SMP KASAN
>>> CPU: 1 PID: 7181 Comm: syz-executor616 Not tainted 5.6.0-syzkaller #0
>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
>>> RIP: 0010:page_to_nid include/linux/mm.h:1245 [inline]
>>> RIP: 0010:lookup_node mm/mempolicy.c:906 [inline]
>>> RIP: 0010:do_get_mempolicy mm/mempolicy.c:970 [inline]
>>> RIP: 0010:kernel_get_mempolicy+0x60e/0xfb0 mm/mempolicy.c:1615
>>> Code: 88 00 07 00 00 e8 b2 35 c5 ff 4c 8b 7c 24 78 48 b8 00 00 00 00 00 fc ff df 4c 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 fb 08 00 00 <49> 8b 1f 48 c7 c7 ff ff ff ff 48 89 de e8 10 37 c5 ff 48 83 fb ff
>>> RSP: 0018:ffffc900018d7de8 EFLAGS: 00010246
>>> RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff81adaaf1
>>> RDX: 1fffffffe0000000 RSI: ffffffff81adaafe RDI: 0000000000000005
>>> RBP: 0000000000000000 R08: ffff88808de924c0 R09: ffffed1011bd2499
>>> R10: ffff88808de924c7 R11: ffffed1011bd2498 R12: 0000000000000000
>>> R13: 1ffff9200031afc4 R14: ffffffff89a6df60 R15: ffffffff00000000
>>> FS:  00007f848cd4a700(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
>>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> CR2: ffffffff00000000 CR3: 00000000a7a8d000 CR4: 00000000001406e0
>>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>>> Call Trace:
>>>  __do_sys_get_mempolicy mm/mempolicy.c:1633 [inline]
>>>  __se_sys_get_mempolicy mm/mempolicy.c:1629 [inline]
>>>  __x64_sys_get_mempolicy+0xba/0x150 mm/mempolicy.c:1629
>>>  do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
>>>  entry_SYSCALL_64_after_hwframe+0x49/0xb3
>>> RIP: 0033:0x446719
>>> Code: e8 5c b3 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 0b 08 fc ff c3 66 2e 0f 1f 84 00 00 00 00
>>> RSP: 002b:00007f848cd49db8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ef
>>> RAX: ffffffffffffffda RBX: 00000000006dbc28 RCX: 0000000000446719
>>> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
>>> RBP: 00000000006dbc20 R08: 0000000000000003 R09: 0000000000000000
>>> R10: 000000002073b000 R11: 0000000000000246 R12: 00000000006dbc2c
>>> R13: 00007ffcfe6ba66f R14: 00007f848cd4a9c0 R15: 20c49ba5e353f7cf
>>> Modules linked in:
>>> CR2: ffffffff00000000
>>> ---[ end trace 0becf554e06291c3 ]---
>>> RIP: 0010:page_to_nid include/linux/mm.h:1245 [inline]
>>> RIP: 0010:lookup_node mm/mempolicy.c:906 [inline]
>>> RIP: 0010:do_get_mempolicy mm/mempolicy.c:970 [inline]
>>> RIP: 0010:kernel_get_mempolicy+0x60e/0xfb0 mm/mempolicy.c:1615
>>> Code: 88 00 07 00 00 e8 b2 35 c5 ff 4c 8b 7c 24 78 48 b8 00 00 00 00 00 fc ff df 4c 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 fb 08 00 00 <49> 8b 1f 48 c7 c7 ff ff ff ff 48 89 de e8 10 37 c5 ff 48 83 fb ff
>>> RSP: 0018:ffffc900018d7de8 EFLAGS: 00010246
>>> RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff81adaaf1
>>> RDX: 1fffffffe0000000 RSI: ffffffff81adaafe RDI: 0000000000000005
>>> RBP: 0000000000000000 R08: ffff88808de924c0 R09: ffffed1011bd2499
>>> R10: ffff88808de924c7 R11: ffffed1011bd2498 R12: 0000000000000000
>>> R13: 1ffff9200031afc4 R14: ffffffff89a6df60 R15: ffffffff00000000
>>> FS:  00007f848cd4a700(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
>>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> CR2: ffffffff00000000 CR3: 00000000a7a8d000 CR4: 00000000001406e0
>>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> 
>> Hi, Andrew & all,
>> 
>> I can reproduce this locally right after I run the test program, and
>> below patch fixed it for me - the test program can run with quite a
>> few minutes without crashing again.
>> 
>> Is there a way I can feed this to the syzbot to re-verify this?
>
> Hi Peter,
>
> Send the patch. At the top of the email, put something like
> #syz test <git repo> <branch>

want 2 args (repo, branch), got 3

>
> It's documented here:
> https://github.com/google/syzkaller/blob/master/docs/syzbot.md
>
>
>> Thanks,
>> 
>> 8<---------------------------------------------------------------
>> From 23800bff6fa346a4e9b3806dc0cfeb74498df757 Mon Sep 17 00:00:00 2001
>> From: Peter Xu <peterx@...hat.com>
>> Date: Mon, 6 Apr 2020 20:40:13 -0400
>> Subject: [PATCH] mm/mempolicy: Allow lookup_node() to handle fatal signal
>> 
>> lookup_node() uses gup to pin the page and get node information.  It
>> checks against ret>=0 assuming the page will be filled in.  However
>> it's also possible that gup will return zero, for example, when the
>> thread is quickly killed with a fatal signal.  Teach lookup_node() to
>> gracefully return an error -EFAULT if it happens.
>> 
>> Reported-by: syzbot+693dc11fcb53120b5559@...kaller.appspotmail.com
>> Fixes: 4426e945df58 ("mm/gup: allow VM_FAULT_RETRY for multiple times")
>> Signed-off-by: Peter Xu <peterx@...hat.com>
>> ---
>>  mm/mempolicy.c | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>> 
>> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
>> index 5fb427aed612..1398578db025 100644
>> --- a/mm/mempolicy.c
>> +++ b/mm/mempolicy.c
>> @@ -902,7 +902,10 @@ static int lookup_node(struct mm_struct *mm, unsigned long addr)
>>  
>>  	int locked = 1;
>>  	err = get_user_pages_locked(addr & PAGE_MASK, 1, 0, &p, &locked);
>> -	if (err >= 0) {
>> +	if (err == 0) {
>> +		/* E.g. GUP interupted by fatal signal */
>> +		err = -EFAULT;
>> +	} else if (err > 0) {
>>  		err = page_to_nid(p);
>>  		put_page(p);
>>  	}
>> 
>
>
>
> -- 
> ~Randy
> Reported-by: Randy Dunlap <rdunlap@...radead.org>
>
> -- 
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