Date:   Fri, 10 May 2019 07:09:23 +0200
From:   Christian Brauner <christian@...uner.io>
To:     syzbot <syzbot+3286e58549edc479faae@...kaller.appspotmail.com>,
        akpm@...ux-foundation.org, arnd@...db.de, arunks@...eaurora.org,
        cyphar@...har.com, dhowells@...hat.com, ebiederm@...ssion.com,
        elena.reshetova@...el.com, guro@...com, jannh@...gle.com,
        keescook@...omium.org, linux-kernel@...r.kernel.org,
        luto@...capital.net, luto@...nel.org, mhocko@...e.com,
        mingo@...nel.org, mtk.manpages@...il.com, namit@...are.com,
        oleg@...hat.com, peterz@...radead.org, riel@...riel.com,
        shakeelb@...gle.com, syzkaller-bugs@...glegroups.com,
        tglx@...utronix.de, torvalds@...ux-foundation.org,
        viro@...iv.linux.org.uk, wad@...omium.org
Subject: Re: WARNING: locking bug in copy_process

On May 10, 2019 3:07:05 AM GMT+02:00, syzbot <syzbot+3286e58549edc479faae@...kaller.appspotmail.com> wrote:
>Hello,
>
>syzbot found the following crash on:
>
>HEAD commit:    a2d635de Merge tag 'drm-next-2019-05-09' of
>git://anongit...
>git tree:       upstream
>console output:
>https://syzkaller.appspot.com/x/log.txt?x=12b36dd0a00000
>kernel config: 
>https://syzkaller.appspot.com/x/.config?x=2ef407aed78c3758
>dashboard link:
>https://syzkaller.appspot.com/bug?extid=3286e58549edc479faae
>compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
>userspace arch: i386
>syz repro:     
>https://syzkaller.appspot.com/x/repro.syz?x=12d85ec8a00000
>C reproducer:  
>https://syzkaller.appspot.com/x/repro.c?x=11df8778a00000
>
>The bug was bisected to:
>
>commit b3e5838252665ee4cfa76b82bdf1198dca81e5be
>Author: Christian Brauner <christian@...uner.io>
>Date:   Wed Mar 27 12:04:15 2019 +0000
>
>     clone: add CLONE_PIDFD
>
>bisection log: 
>https://syzkaller.appspot.com/x/bisect.txt?x=14fe77b4a00000
>final crash:   
>https://syzkaller.appspot.com/x/report.txt?x=16fe77b4a00000
>console output:
>https://syzkaller.appspot.com/x/log.txt?x=12fe77b4a00000
>
>IMPORTANT: if you fix the bug, please add the following tag to the
>commit:
>Reported-by: syzbot+3286e58549edc479faae@...kaller.appspotmail.com
>Fixes: b3e583825266 ("clone: add CLONE_PIDFD")
>
>  entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
>RIP: 0023:0xf7fec849
>Code: 85 d2 74 02 89 0a 5b 5d c3 8b 04 24 c3 8b 14 24 c3 8b 3c 24 c3 90
>90  
>90 90 90 90 90 90 90 90 90 90 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3
>90  
>90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
>RSP: 002b:00000000ffed5a8c EFLAGS: 00000246 ORIG_RAX: 0000000000000078
>RAX: ffffffffffffffda RBX: 0000000000003ffc RCX: 0000000000000000
>RDX: 00000000200005c0 RSI: 0000000000000000 RDI: 0000000000000000
>RBP: 0000000000000012 R08: 0000000000000000 R09: 0000000000000000
>R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
>R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
>------------[ cut here ]------------
>DEBUG_LOCKS_WARN_ON(depth <= 0)
>WARNING: CPU: 1 PID: 7744 at kernel/locking/lockdep.c:4052
>__lock_release  
>kernel/locking/lockdep.c:4052 [inline]
>WARNING: CPU: 1 PID: 7744 at kernel/locking/lockdep.c:4052  
>lock_release+0x667/0xa00 kernel/locking/lockdep.c:4321
>Kernel panic - not syncing: panic_on_warn set ...
>CPU: 1 PID: 7744 Comm: syz-executor007 Not tainted 5.1.0+ #4
>Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> 
>Google 01/01/2011
>Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x172/0x1f0 lib/dump_stack.c:113
>  panic+0x2cb/0x65c kernel/panic.c:214
>  __warn.cold+0x20/0x45 kernel/panic.c:566
>  report_bug+0x263/0x2b0 lib/bug.c:186
>  fixup_bug arch/x86/kernel/traps.c:179 [inline]
>  fixup_bug arch/x86/kernel/traps.c:174 [inline]
>  do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:272
>  do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:291
>  invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:972
>RIP: 0010:__lock_release kernel/locking/lockdep.c:4052 [inline]
>RIP: 0010:lock_release+0x667/0xa00 kernel/locking/lockdep.c:4321
>Code: 0f 85 a0 03 00 00 8b 35 77 66 08 08 85 f6 75 23 48 c7 c6 a0 55 6b
>87  
>48 c7 c7 40 25 6b 87 4c 89 85 70 ff ff ff e8 b7 a9 eb ff <0f> 0b 4c 8b
>85  
>70 ff ff ff 4c 89 ea 4c 89 e6 4c 89 c7 e8 52 63 ff
>RSP: 0018:ffff888094117b48 EFLAGS: 00010086
>RAX: 0000000000000000 RBX: 1ffff11012822f6f RCX: 0000000000000000
>RDX: 0000000000000000 RSI: ffffffff815af236 RDI: ffffed1012822f5b
>RBP: ffff888094117c00 R08: ffff888092bfc400 R09: fffffbfff113301d
>R10: fffffbfff113301c R11: ffffffff889980e3 R12: ffffffff8a451df8
>R13: ffffffff8142e71f R14: ffffffff8a44cc80 R15: ffff888094117bd8
>  percpu_up_read.constprop.0+0xcb/0x110 include/linux/percpu-rwsem.h:92
> cgroup_threadgroup_change_end include/linux/cgroup-defs.h:712 [inline]
>  copy_process.part.0+0x47ff/0x6710 kernel/fork.c:2222
>  copy_process kernel/fork.c:1772 [inline]
>  _do_fork+0x25d/0xfd0 kernel/fork.c:2338
>  __do_compat_sys_x86_clone arch/x86/ia32/sys_ia32.c:240 [inline]
>  __se_compat_sys_x86_clone arch/x86/ia32/sys_ia32.c:236 [inline]
>  __ia32_compat_sys_x86_clone+0xbc/0x140 arch/x86/ia32/sys_ia32.c:236
>  do_syscall_32_irqs_on arch/x86/entry/common.c:334 [inline]
>  do_fast_syscall_32+0x281/0xd54 arch/x86/entry/common.c:405
>  entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
>RIP: 0023:0xf7fec849
>Code: 85 d2 74 02 89 0a 5b 5d c3 8b 04 24 c3 8b 14 24 c3 8b 3c 24 c3 90
>90  
>90 90 90 90 90 90 90 90 90 90 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3
>90  
>90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
>RSP: 002b:00000000ffed5a8c EFLAGS: 00000246 ORIG_RAX: 0000000000000078
>RAX: ffffffffffffffda RBX: 0000000000003ffc RCX: 0000000000000000
>RDX: 00000000200005c0 RSI: 0000000000000000 RDI: 0000000000000000
>RBP: 0000000000000012 R08: 0000000000000000 R09: 0000000000000000
>R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
>R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
>Kernel Offset: disabled
>Rebooting in 86400 seconds..
>
>
>---
>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#status for how to communicate with syzbot.
>For information about bisection process see:
>https://goo.gl/tpsmEJ#bisection
>syzbot can test patches for this bug, for details see:
>https://goo.gl/tpsmEJ#testing-patches

I think I know how this comes about.
I'll send a patch later today.

Christian

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