Re: general protection fault in locks_remove_flock

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit:    d881de30d29e Add linux-next specific files for 20181107
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=10a0102b400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=caa433e1c8778437
dashboard link: https://syzkaller.appspot.com/bug?extid=2400c924363a9a43d116
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14b42f5b400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=151777e5400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+2400c924363a9a43d116@xxxxxxxxxxxxxxxxxxxxxxxxx

audit: type=1800 audit(1541602996.121:30): pid=5502 uid=0 auid=4294967295  
ses=4294967295 subj==unconfined op=collect_data cause=failed(directio)  
comm="startpar" name="rmnologin" dev="sda1" ino=2423 res=0
kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 5657 Comm: syz-executor710 Not tainted  
4.20.0-rc1-next-20181107+ #107
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:locks_remove_flock+0x216/0x350 fs/locks.c:2567
Code: 00 0f 85 3a 01 00 00 48 8b 5b 98 48 85 db 74 3a e8 1f 41 92 ff 48 8d  
7b 08 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f  
85 17 01 00 00 48 8b 5b 08 48 85 db 74 0d e8 f2 40
RSP: 0018:ffff8801b9dc72c0 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: 1ffff100373b8e89 RCX: ffffffff81ed555d
RDX: 03fffe2006e771d2 RSI: ffffffff81ed5c71 RDI: 1ffff100373b8e91
RBP: ffff8801b9dc74a0 R08: ffff8801b9dbc480 R09: ffffed003b5e5b67
R10: ffffed003b5e5b67 R11: ffff8801daf2db3b R12: ffff8801d88f9c80
R13: ffff8801b9dc7338 R14: 1ffff100373b8e5b R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000002001d000 CR3: 000000000946a000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 locks_remove_file+0x148/0x5c0 fs/locks.c:2607
 __fput+0x2f0/0xa70 fs/file_table.c:271
 ____fput+0x15/0x20 fs/file_table.c:312
 task_work_run+0x1e8/0x2a0 kernel/task_work.c:113
 exit_task_work include/linux/task_work.h:22 [inline]
 do_exit+0x1ad1/0x26d0 kernel/exit.c:867
 do_group_exit+0x177/0x440 kernel/exit.c:970
 __do_sys_exit_group kernel/exit.c:981 [inline]
 __se_sys_exit_group kernel/exit.c:979 [inline]
 __x64_sys_exit_group+0x3e/0x50 kernel/exit.c:979
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x43ede8
Code: Bad RIP value.
RSP: 002b:00007ffe7a46fe78 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000000043ede8
RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000
RBP: 00000000004beea8 R08: 00000000000000e7 R09: ffffffffffffffd0
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00000000006d1180 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
---[ end trace a84b3ae501385451 ]---
RIP: 0010:locks_remove_flock+0x216/0x350 fs/locks.c:2567
Code: 00 0f 85 3a 01 00 00 48 8b 5b 98 48 85 db 74 3a e8 1f 41 92 ff 48 8d  
7b 08 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 0f  
85 17 01 00 00 48 8b 5b 08 48 85 db 74 0d e8 f2 40
RSP: 0018:ffff8801b9dc72c0 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: 1ffff100373b8e89 RCX: ffffffff81ed555d
RDX: 03fffe2006e771d2 RSI: ffffffff81ed5c71 RDI: 1ffff100373b8e91
RBP: ffff8801b9dc74a0 R08: ffff8801b9dbc480 R09: ffffed003b5e5b67
R10: ffffed003b5e5b67 R11: ffff8801daf2db3b R12: ffff8801d88f9c80
R13: ffff8801b9dc7338 R14: 1ffff100373b8e5b R15: dffffc0000000000
FS:  000000000229b880(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000043edbe CR3: 000000000946a000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400