refcount_t: underflow; use-after-free.
------------[ cut here ]------------
WARNING: CPU: 0 PID: 7040 at lib/refcount.c:281 refcount_dec_not_one.cold+0x18/0x25 lib/refcount.c:281
Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 7040 Comm: syz-executor.0 Not tainted 4.14.304-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/12/2023
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x1b2/0x281 lib/dump_stack.c:58
 panic+0x1f9/0x42d kernel/panic.c:183
 __warn.cold+0x20/0x44 kernel/panic.c:547
 report_bug+0x208/0x250 lib/bug.c:183
 fixup_bug arch/x86/kernel/traps.c:177 [inline]
 fixup_bug arch/x86/kernel/traps.c:172 [inline]
 do_error_trap+0x195/0x2d0 arch/x86/kernel/traps.c:295
 invalid_op+0x1b/0x40 arch/x86/entry/entry_64.S:967
RIP: 0010:refcount_dec_not_one.cold+0x18/0x25 lib/refcount.c:281
RSP: 0018:ffff8880a2e675e8 EFLAGS: 00010282
RAX: 0000000000000026 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 000000000000d9c0 RSI: ffffffff81444260 RDI: ffffed10145cceb3
RBP: ffff8880925ecb58 R08: 0000000000000026 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 00000000ffffffff
R13: 0000000000000000 R14: 0000000000000000 R15: ffff8880925ecb68
 refcount_dec_and_mutex_lock+0x1a/0x60 lib/refcount.c:309
 nbd_put drivers/block/nbd.c:228 [inline]
 nbd_config_put+0x442/0x6c0 drivers/block/nbd.c:1172
 nbd_genl_connect+0xcb9/0x13e0 drivers/block/nbd.c:1903
 genl_family_rcv_msg+0x572/0xb20 net/netlink/genetlink.c:600
 genl_rcv_msg+0xaf/0x140 net/netlink/genetlink.c:625
 netlink_rcv_skb+0x125/0x390 net/netlink/af_netlink.c:2454
 genl_rcv+0x24/0x40 net/netlink/genetlink.c:636
 netlink_unicast_kernel net/netlink/af_netlink.c:1296 [inline]
 netlink_unicast+0x437/0x610 net/netlink/af_netlink.c:1322
 netlink_sendmsg+0x648/0xbc0 net/netlink/af_netlink.c:1893
 sock_sendmsg_nosec net/socket.c:646 [inline]
 sock_sendmsg+0xb5/0x100 net/socket.c:656
 ___sys_sendmsg+0x6c8/0x800 net/socket.c:2062
 __sys_sendmsg+0xa3/0x120 net/socket.c:2096
 SYSC_sendmsg net/socket.c:2107 [inline]
 SyS_sendmsg+0x27/0x40 net/socket.c:2103
 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x5e/0xd3
RIP: 0033:0x7f0e15cc80c9
RSP: 002b:00007f0e1423a168 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f0e15de7f80 RCX: 00007f0e15cc80c9
RDX: 0000000000000000 RSI: 0000000020000140 RDI: 0000000000000005
RBP: 00007f0e15d23ae9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffcc139b6df R14: 00007f0e1423a300 R15: 0000000000022000
Kernel Offset: disabled
Rebooting in 86400 seconds..