refcount_t: underflow; use-after-free.
 d_alloc_name+0x71/0x90 fs/dcache.c:1758
 proc_setup_self+0xc3/0x38a fs/proc/self.c:42
------------[ cut here ]------------
 proc_fill_super+0x247/0x2e6 fs/proc/inode.c:513
WARNING: CPU: 0 PID: 12521 at lib/refcount.c:187 refcount_sub_and_test lib/refcount.c:187 [inline]
WARNING: CPU: 0 PID: 12521 at lib/refcount.c:187 refcount_sub_and_test.cold+0x18/0x22 lib/refcount.c:177
 mount_ns+0xec/0x190 fs/super.c:1051
Kernel panic - not syncing: panic_on_warn set ...

 proc_mount+0x6a/0xa0 fs/proc/root.c:101
 mount_fs+0x97/0x2a1 fs/super.c:1237
 vfs_kern_mount.part.0+0x5e/0x3d0 fs/namespace.c:1046
 vfs_kern_mount fs/namespace.c:1036 [inline]
 kern_mount_data+0x56/0xc0 fs/namespace.c:3329
 pid_ns_prepare_proc+0x1e/0x90 fs/proc/root.c:222
 alloc_pid+0x9ef/0xc70 kernel/pid.c:324
 copy_process.part.0+0x272f/0x6a00 kernel/fork.c:1794
 copy_process kernel/fork.c:1595 [inline]
 _do_fork+0x19e/0xce0 kernel/fork.c:2085
 SYSC_clone kernel/fork.c:2195 [inline]
 SyS_clone+0x37/0x50 kernel/fork.c:2189
 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x459879
RSP: 002b:00007f1b3ebc8c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 00007f1b3ebc8c90 RCX: 0000000000459879
RDX: 9999999999999999 RSI: 0000000000000000 RDI: 0000000020000100
RBP: 000000000075bf20 R08: ffffffffffffffff R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f1b3ebc96d4
R13: 00000000004bfd46 R14: 00000000004d1af8 R15: 0000000000000004
CPU: 0 PID: 12521 Comm: syz-executor.0 Not tainted 4.14.140 #36
kobject: 'loop5' (ffff8880a4a6f7e0): fill_kobj_path: path = '/devices/virtual/block/loop5'
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x138/0x197 lib/dump_stack.c:53
 panic+0x1f2/0x426 kernel/panic.c:182
proc_fill_super: can't allocate /proc/self
 __warn.cold+0x2f/0x36 kernel/panic.c:546
 report_bug+0x216/0x254 lib/bug.c:186
 fixup_bug arch/x86/kernel/traps.c:177 [inline]
 fixup_bug arch/x86/kernel/traps.c:172 [inline]
 do_error_trap+0x1bb/0x310 arch/x86/kernel/traps.c:295
 do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:314
 invalid_op+0x1b/0x40 arch/x86/entry/entry_64.S:963
RIP: 0010:refcount_sub_and_test lib/refcount.c:187 [inline]
RIP: 0010:refcount_sub_and_test.cold+0x18/0x22 lib/refcount.c:177
RSP: 0018:ffff88805195faf8 EFLAGS: 00010286
RAX: 0000000000000026 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000040000 RSI: ffffffff814b2d45 RDI: ffffed100a32bf55
RBP: ffff88805195fb20 R08: 0000000000000026 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8880514a0380
R13: 0000000000000001 R14: 00000000ffffffff R15: 0000000020000100
 refcount_dec_and_test+0x1b/0x20 lib/refcount.c:212
 kref_put include/linux/kref.h:69 [inline]
 put_pid_ns+0x55/0x110 kernel/pid_namespace.c:203
 free_nsproxy+0x103/0x200 kernel/nsproxy.c:182
 switch_task_namespaces+0x98/0xb0 kernel/nsproxy.c:229
 exit_task_namespaces+0x18/0x20 kernel/nsproxy.c:234
 copy_process.part.0+0x3b59/0x6a00 kernel/fork.c:1986
 copy_process kernel/fork.c:1595 [inline]
 _do_fork+0x19e/0xce0 kernel/fork.c:2085
 SYSC_clone kernel/fork.c:2195 [inline]
 SyS_clone+0x37/0x50 kernel/fork.c:2189
 do_syscall_64+0x1e8/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x459879
RSP: 002b:00007f3168c4bc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 00007f3168c4bc90 RCX: 0000000000459879
RDX: 9999999999999999 RSI: 0000000000000000 RDI: 0000000020000100
RBP: 000000000075bf20 R08: ffffffffffffffff R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f3168c4c6d4
R13: 00000000004bfd46 R14: 00000000004d1af8 R15: 0000000000000004
Kernel Offset: disabled
Rebooting in 86400 seconds..