linux-kernel - Re: BUG: unable to handle kernel NULL pointer dereference in unlink_file

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Message-ID: <CACT4Y+bNLT90b37QizA=W3acrWmhG0+xGv3a8Gw0N5zKTvLnzA@mail.gmail.com>
Date:   Mon, 31 Dec 2018 08:49:46 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     syzbot <syzbot+4cbac4707f8e5215007b@...kaller.appspotmail.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Souptick Joarder <jrdr.linux@...il.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>, linux@...inikbrodowski.net,
        Michal Hocko <mhocko@...e.com>,
        David Rientjes <rientjes@...gle.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: BUG: unable to handle kernel NULL pointer dereference in unlink_file_vma

On Mon, Dec 31, 2018 at 8:44 AM syzbot
<syzbot+4cbac4707f8e5215007b@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit:    3d647e62686f Merge tag 's390-4.19-4' of git://git.kernel.o..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1316f4a5400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=88e9a8a39dc0be2d
> dashboard link: https://syzkaller.appspot.com/bug?extid=4cbac4707f8e5215007b
> compiler:       gcc (GCC) 8.0.1 20180413 (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+4cbac4707f8e5215007b@...kaller.appspotmail.com

Since this involves OOMs and looks like a one-off induced memory corruption:

#syz dup: kernel panic: corrupted stack end in wb_workfn

> RAX: 0000000000000002 RBX: 00000000ffffffff RCX: 000000000045df89
> RDX: 0000000000000080 RSI: 000000c420033890 RDI: 0000000000000004
> RBP: 000000c420033e90 R08: 0000000000000003 R09: 000000c420000d80
> R10: 00000000ffffffff R11: 0000000000000246 R12: 0000000000000001
> R13: 000000c42f90d718 R14: 0000000000000066 R15: 000000c42f90d708
> BUG: unable to handle kernel NULL pointer dereference at 0000000000000068
> PGD 1d85b1067 P4D 1d85b1067 PUD 1cd360067 PMD 0
> Oops: 0002 [#1] PREEMPT SMP KASAN
> CPU: 1 PID: 2748 Comm: syz-executor0 Not tainted 4.19.0-rc7+ #55
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:__down_write arch/x86/include/asm/rwsem.h:142 [inline]
> RIP: 0010:down_write+0x97/0x130 kernel/locking/rwsem.c:72
> Code: a5 f9 31 d2 45 31 c9 41 b8 01 00 00 00 ff 75 08 48 8d 7b 60 31 c9 31
> f6 e8 c6 01 b1 f9 48 89 d8 48 ba 01 00 00 00 ff ff ff ff <f0> 48 0f c1 10
> 85 d2 74 05 e8 3b 29 fe ff 48 8d 7d a0 5a 48 89 f8
> RSP: 0000:ffff880128396ff0 EFLAGS: 00010246
> RAX: 0000000000000068 RBX: 0000000000000068 RCX: 0000000000000000
> RDX: ffffffff00000001 RSI: 0000000000000000 RDI: 0000000000000286
> RBP: ffff880128397078 R08: 0000000000000001 R09: 0000000000000000
> R10: ffff8801ce8da278 R11: 0000000000000000 R12: 1ffff10025072dff
> R13: 0000000000000068 R14: dffffc0000000000 R15: 00007fca701da000
> FS:  00007fca6ebd9700(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000000068 CR3: 00000001d88cd000 CR4: 00000000001406e0
> kobject: 'syz_tun' (00000000bb2f2151): kobject_cleanup, parent
> (null)
> Call Trace:
>   i_mmap_lock_write include/linux/fs.h:482 [inline]
>   unlink_file_vma+0x75/0xb0 mm/mmap.c:166
>   free_pgtables+0x279/0x380 mm/memory.c:641
>   exit_mmap+0x2cd/0x590 mm/mmap.c:3094
>   __mmput kernel/fork.c:1001 [inline]
>   mmput+0x247/0x610 kernel/fork.c:1022
>   exit_mm kernel/exit.c:545 [inline]
>   do_exit+0xe6f/0x2610 kernel/exit.c:854
>   do_group_exit+0x177/0x440 kernel/exit.c:970
>   get_signal+0x8b0/0x1980 kernel/signal.c:2513
>   do_signal+0x9c/0x21e0 arch/x86/kernel/signal.c:816
>   exit_to_usermode_loop+0x2e5/0x380 arch/x86/entry/common.c:162
>   prepare_exit_to_usermode arch/x86/entry/common.c:197 [inline]
>   syscall_return_slowpath arch/x86/entry/common.c:268 [inline]
>   do_syscall_64+0x6be/0x820 arch/x86/entry/common.c:293
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x457579
> Code: 24 08 48 89 01 e8 d7 2d fc ff e8 22 7a fc ff b8 02 00 00 00 48 8d 0d
> 6a 60 09 01 87 01 8b 05 62 60 09 01 83 f8 01 0f 85 8a 00 <00> 00 b8 01 00
> 00 00 88 05 9e 65 09 01 84 c0 74 72 b8 01 00 00 00
> RSP: 002b:00007fca6ebd8cf8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
> RAX: fffffffffffffe00 RBX: 000000000072bf08 RCX: 0000000000457579
> RDX: 0000000000000000 RSI: 0000000000000080 RDI: 000000000072bf08
> RBP: 000000000072bf00 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 000000000072bf0c
> R13: 00007ffd2b23c63f R14: 00007fca6ebd99c0 R15: 0000000000000000
> Modules linked in:
> CR2: 0000000000000068
> ---[ end trace ea9ba926f44bc95e ]---
> RIP: 0010:__down_write arch/x86/include/asm/rwsem.h:142 [inline]
> RIP: 0010:down_write+0x97/0x130 kernel/locking/rwsem.c:72
> Code: a5 f9 31 d2 45 31 c9 41 b8 01 00 00 00 ff 75 08 48 8d 7b 60 31 c9 31
> f6 e8 c6 01 b1 f9 48 89 d8 48 ba 01 00 00 00 ff ff ff ff <f0> 48 0f c1 10
> 85 d2 74 05 e8 3b 29 fe ff 48 8d 7d a0 5a 48 89 f8
> RSP: 0000:ffff880128396ff0 EFLAGS: 00010246
> RAX: 0000000000000068 RBX: 0000000000000068 RCX: 0000000000000000
> RDX: ffffffff00000001 RSI: 0000000000000000 RDI: 0000000000000286
> RBP: ffff880128397078 R08: 0000000000000001 R09: 0000000000000000
> R10: ffff8801ce8da278 R11: 0000000000000000 R12: 1ffff10025072dff
> R13: 0000000000000068 R14: dffffc0000000000 R15: 00007fca701da000
> FS:  00007fca6ebd9700(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 0000000000000068 CR3: 00000001d88cd000 CR4: 00000000001406e0
>
>
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@...glegroups.com.
>
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
> syzbot.
>
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