Re: general protection fault in __list_del_entry_valid (2)

[Michal Hocko]

On Sun 17-12-17 07:47:01, syzbot wrote:
> syzkaller has found reproducer for the following crash on
> 82bcf1def3b5f1251177ad47c44f7e17af039b4b
> git://git.cmpxchg.org/linux-mmots.git/master
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached
> Raw console output is attached.
> C reproducer is attached
> syzkaller reproducer is attached. See https://goo.gl/kgGztJ
> for information about syzkaller reproducers

This is an unhandled register_shrinker failure in sget_userns (thiggered
by the allocation fault injection).
There has been a fix proposed http://lkml.kernel.org/r/20171123145540.GB21978@xxxxxxxxxxxxxxxxxx
(this one depends on http://lkml.kernel.org/r/1511523385-6433-1-git-send-email-penguin-kernel@xxxxxxxxxxxxxxxxxxx
or http://lkml.kernel.org/r/20171216192937.13549-1-akaraliou.dev@xxxxxxxxx).
 
> R13: 0000000000403940 R14: 0000000000000000 R15: 0000000000000000
> kasan: CONFIG_KASAN_INLINE enabled
> kasan: GPF could be caused by NULL-ptr deref or user memory access
> general protection fault: 0000 [#1] SMP KASAN
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Modules linked in:
> CPU: 1 PID: 3146 Comm: syzkaller259864 Not tainted 4.15.0-rc2-mm1+ #39
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> RIP: 0010:__list_del_entry_valid+0x7e/0x150 lib/list_debug.c:51
> RSP: 0018:ffff8801c4d97b48 EFLAGS: 00010246
> RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: ffff8801c4ac75d8 RDI: ffff8801c4ac75e0
> RBP: ffff8801c4d97b60 R08: ffff8801c4d975c0 R09: ffff8801c5bd2180
> R10: 000000000000000b R11: ffffed00389b2eba R12: 0000000000000000
> R13: dffffc0000000000 R14: 1ffff100389b2f8d R15: ffff8801c4ac75d8
> FS:  0000000001689940(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000207caf71 CR3: 00000001c5f99002 CR4: 00000000001606e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  __list_del_entry include/linux/list.h:117 [inline]
>  list_del include/linux/list.h:125 [inline]
>  unregister_shrinker+0x79/0x300 mm/vmscan.c:285
>  deactivate_locked_super+0x64/0xd0 fs/super.c:311
>  deactivate_super+0x141/0x1b0 fs/super.c:343
>  cleanup_mnt+0xb2/0x150 fs/namespace.c:1173
>  __cleanup_mnt+0x16/0x20 fs/namespace.c:1180
>  task_work_run+0x199/0x270 kernel/task_work.c:113
>  tracehook_notify_resume include/linux/tracehook.h:191 [inline]
>  exit_to_usermode_loop+0x275/0x2f0 arch/x86/entry/common.c:165
>  prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
>  syscall_return_slowpath+0x490/0x550 arch/x86/entry/common.c:264
>  entry_SYSCALL_64_fastpath+0x94/0x96
> RIP: 0033:0x446679
> RSP: 002b:00007ffccb258058 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
> RAX: ffffffffffffffec RBX: 00007ffccb258000 RCX: 0000000000446679
> RDX: 0000000020f9effa RSI: 00000000202b9000 RDI: 0000000020b85ff8
> RBP: 0000000000000003 R08: 00000000207caf71 R09: 0000000000003531
> R10: 0000000000000000 R11: 0000000000000246 R12: ffffffffffffffff
> R13: 0000000000000006 R14: 0000000000000000 R15: 0000000000000000
> Code: 00 00 00 00 ad de 49 39 c4 74 66 48 b8 00 02 00 00 00 00 ad de 48 89
> da 48 39 c3 74 65 48 c1 ea 03 48 b8 00 00 00 00 00 fc ff df <80> 3c 02 00 75
> 7b 48 8b 13 48 39 f2 75 57 49 8d 7c 24 08 48 b8
> RIP: __list_del_entry_valid+0x7e/0x150 lib/list_debug.c:51 RSP:
> ffff8801c4d97b48
> ---[ end trace 422dd7d3477fece7 ]---
> Kernel panic - not syncing: Fatal exception
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> Kernel Offset: disabled
> Rebooting in 86400 seconds..
-- 
Michal Hocko
SUSE Labs