Re: general protection fault in __x86_indirect_thunk_rbx

[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=169e9825400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=caa433e1c8778437
dashboard link: https://syzkaller.appspot.com/bug?extid=83e12cf81d2c14842146
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15bd9447400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1121d82b400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+83e12cf81d2c14842146@xxxxxxxxxxxxxxxxxxxxxxxxx

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: 5670 Comm: syz-executor439 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:__x86_indirect_thunk_rbx+0x10/0x20 arch/x86/lib/retpoline.S:33
Code: 90 0f ae e8 eb f9 48 89 04 24 c3 0f 1f 44 00 00 66 2e 0f 1f 84 00 00  
00 00 00 e8 07 00 00 00 f3 90 0f ae e8 eb f9 48 89 1c 24 <c3> 0f 1f 44 00  
00 66 2e 0f 1f 84 00 00 00 00 00 e8 07 00 00 00 f3
RSP: 0018:ffff8801d89af2b0 EFLAGS: 00010293
RAX: ffff8801d49723c0 RBX: 894cdffffc000000 RCX: ffffffff81ed555d
RDX: 0000000000000000 RSI: ffffffff81ed5c9e RDI: ffff8801d89af338
RBP: ffff8801d89af4a0 R08: ffff8801d49723c0 R09: ffffed003b5e5b67
R10: ffffed003b5e5b67 R11: ffff8801daf2db3b R12: ffff8801d798da00
R13: ffff8801d89af338 R14: 1ffff1003b135e5b R15: dffffc0000000000
FS:  0000000001292880(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020e2aff8 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: 0033:0x43ec48
Code: Bad RIP value.
RSP: 002b:00007fff104a8308 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000000043ec48
RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000
RBP: 00000000004be508 R08: 00000000000000e7 R09: ffffffffffffffd0
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00000000006d0180 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
---[ end trace db9bef1a2174e463 ]---
RIP: 0010:__x86_indirect_thunk_rbx+0x10/0x20 arch/x86/lib/retpoline.S:33
Code: 90 0f ae e8 eb f9 48 89 04 24 c3 0f 1f 44 00 00 66 2e 0f 1f 84 00 00  
00 00 00 e8 07 00 00 00 f3 90 0f ae e8 eb f9 48 89 1c 24 <c3> 0f 1f 44 00  
00 66 2e 0f 1f 84 00 00 00 00 00 e8 07 00 00 00 f3
RSP: 0018:ffff8801d89af2b0 EFLAGS: 00010293
RAX: ffff8801d49723c0 RBX: 894cdffffc000000 RCX: ffffffff81ed555d
RDX: 0000000000000000 RSI: ffffffff81ed5c9e RDI: ffff8801d89af338
RBP: ffff8801d89af4a0 R08: ffff8801d49723c0 R09: ffffed003b5e5b67
R10: ffffed003b5e5b67 R11: ffff8801daf2db3b R12: ffff8801d798da00
R13: ffff8801d89af338 R14: 1ffff1003b135e5b R15: dffffc0000000000
FS:  0000000001292880(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000043ec1e CR3: 000000000946a000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400