general protection fault in lockref_get

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    7c1b097f27bf Add linux-next specific files for 20180912
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1333df01400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5980033172920ec0
dashboard link: https://syzkaller.appspot.com/bug?extid=5dc733a19636067b82fd
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+5dc733a19636067b82fd@xxxxxxxxxxxxxxxxxxxxxxxxx

random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: cc1: uninitialized urandom read (8 bytes read)
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: 5580 Comm: syz-executor0 Not tainted 4.19.0-rc3-next-20180912+  
#72
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:__lock_acquire+0x237/0x4ec0 kernel/locking/lockdep.c:3291
Code: 28 00 00 00 0f 85 aa 33 00 00 48 8d 65 d8 5b 41 5c 41 5d 41 5e 41 5f  
5d c3 48 b8 00 00 00 00 00 fc ff df 4c 89 ea 48 c1 ea 03 <80> 3c 02 00 0f  
85 6d 35 00 00 49 81 7d 00 20 90 9e 8a 0f 84 54 ff
RSP: 0018:ffff8801d36ff430 EFLAGS: 00010006
RAX: dffffc0000000000 RBX: 1ffff1003a6dff03 RCX: 0000000000000000
RDX: 0000000140000014 RSI: 0000000000000000 RDI: ffffffff89722928
RBP: ffff8801d36ff7c0 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000000
R13: 0000000a000000a0 R14: ffff8801b9cde100 R15: 0000000000000000
FS:  0000000000db8940(0000) GS:ffff8801dad00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000482e00 CR3: 00000001b9d4f000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 lock_acquire+0x1ed/0x520 kernel/locking/lockdep.c:3901
 __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
 _raw_spin_lock+0x2d/0x40 kernel/locking/spinlock.c:144
 lockref_get+0x15/0x50 include/linux/spinlock.h:329
 dget include/linux/dcache.h:322 [inline]
 mqueue_get_tree+0x101/0x2e0 ipc/mqueue.c:362
 vfs_get_tree+0x1cb/0x5c0 fs/super.c:1787
 mq_create_mount+0xe3/0x190 ipc/mqueue.c:415
 mq_init_ns+0x15a/0x210 ipc/mqueue.c:1621
 create_ipc_ns ipc/namespace.c:58 [inline]
 copy_ipcs+0x3d2/0x580 ipc/namespace.c:84
 create_new_namespaces+0x376/0x900 kernel/nsproxy.c:87
 unshare_nsproxy_namespaces+0xc3/0x1f0 kernel/nsproxy.c:206
 ksys_unshare+0x79c/0x10b0 kernel/fork.c:2535
 __do_sys_unshare kernel/fork.c:2603 [inline]
 __se_sys_unshare kernel/fork.c:2601 [inline]
 __x64_sys_unshare+0x31/0x40 kernel/fork.c:2601
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x459d87
Code: 00 00 00 b8 63 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83 3d 8a fb ff c3  
66 2e 0f 1f 84 00 00 00 00 00 66 90 b8 10 01 00 00 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 1d 8a fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffcccf0eee8 EFLAGS: 00000246 ORIG_RAX: 0000000000000110
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000459d87
RDX: 0000000000000000 RSI: 00007ffcccf0eef0 RDI: 0000000008000000
RBP: 0000000000930b28 R08: 0000000000000000 R09: 0000000000000018
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000010
R13: 0000000000412cc0 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
---[ end trace 404378fbbfe9896c ]---
RIP: 0010:__lock_acquire+0x237/0x4ec0 kernel/locking/lockdep.c:3291
Code: 28 00 00 00 0f 85 aa 33 00 00 48 8d 65 d8 5b 41 5c 41 5d 41 5e 41 5f  
5d c3 48 b8 00 00 00 00 00 fc ff df 4c 89 ea 48 c1 ea 03 <80> 3c 02 00 0f  
85 6d 35 00 00 49 81 7d 00 20 90 9e 8a 0f 84 54 ff
RSP: 0018:ffff8801d36ff430 EFLAGS: 00010006
RAX: dffffc0000000000 RBX: 1ffff1003a6dff03 RCX: 0000000000000000
RDX: 0000000140000014 RSI: 0000000000000000 RDI: ffffffff89722928
RBP: ffff8801d36ff7c0 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000000
R13: 0000000a000000a0 R14: ffff8801b9cde100 R15: 0000000000000000
FS:  0000000000db8940(0000) GS:ffff8801dad00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000482e00 CR3: 00000001b9d4f000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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