R13: 00000000004c05df R14: 00000000004d2bf0 R15: 0000000000000005
refcount_t: underflow; use-after-free.
------------[ cut here ]------------
WARNING: CPU: 0 PID: 8863 at lib/refcount.c:187 refcount_sub_and_test lib/refcount.c:187 [inline]
WARNING: CPU: 0 PID: 8863 at lib/refcount.c:187 refcount_sub_and_test.cold+0x18/0x22 lib/refcount.c:177
Kernel panic - not syncing: panic_on_warn set ...

kobject: 'loop2' (ffff8880a496ce60): fill_kobj_path: path = '/devices/virtual/block/loop2'
CPU: 0 PID: 8863 Comm: syz-executor.4 Not tainted 4.14.151 #0
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+0x1f9/0x42d kernel/panic.c:183
kobject: 'loop3' (ffff8880a4a1f760): kobject_uevent_env
 __warn.cold+0x2f/0x2f kernel/panic.c:547
kobject: 'loop3' (ffff8880a4a1f760): fill_kobj_path: path = '/devices/virtual/block/loop3'
 report_bug+0x216/0x254 lib/bug.c:186
kobject: 'loop2' (ffff8880a496ce60): kobject_uevent_env
 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
kobject: 'loop2' (ffff8880a496ce60): fill_kobj_path: path = '/devices/virtual/block/loop2'
 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
kobject: 'kvm' (ffff888219fad6d0): kobject_uevent_env
RSP: 0018:ffff888057f4faf8 EFLAGS: 00010286
RAX: 0000000000000026 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000040000 RSI: ffffffff814b3f65 RDI: ffffed100afe9f55
RBP: ffff888057f4fb20 R08: 0000000000000026 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff88808d9e82c0
R13: 0000000000000001 R14: 00000000ffffffff R15: 0000000020002100
kobject: 'kvm' (ffff888219fad6d0): fill_kobj_path: path = '/devices/virtual/misc/kvm'
 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
kobject: 'kvm' (ffff888219fad6d0): kobject_uevent_env
 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
kobject: 'kvm' (ffff888219fad6d0): kobject_uevent_env
kobject: 'kvm' (ffff888219fad6d0): fill_kobj_path: path = '/devices/virtual/misc/kvm'
 copy_process kernel/fork.c:1595 [inline]
 _do_fork+0x19e/0xce0 kernel/fork.c:2085
kobject: 'kvm' (ffff888219fad6d0): fill_kobj_path: path = '/devices/virtual/misc/kvm'
 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: 0033:0x459f49
RSP: 002b:00007f848c7ebc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 00007f848c7ebc90 RCX: 0000000000459f49
RDX: 9999999999999999 RSI: 0000000000000000 RDI: 0000000020002100
RBP: 000000000075bf20 R08: ffffffffffffffff R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f848c7ec6d4
R13: 00000000004c05df R14: 00000000004d2bf0 R15: 0000000000000005
Kernel Offset: disabled
Rebooting in 86400 seconds..