============================================
WARNING: possible recursive locking detected
4.15.0-rc2-mm1+ #39 Not tainted
--------------------------------------------
syz-executor7/3877 is trying to acquire lock:
 (rtnl_mutex){+.+.}, at: [<000000008c5736ae>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:74

but task is already holding lock:
 (rtnl_mutex){+.+.}, at: [<000000008c5736ae>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:74

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(rtnl_mutex);
  lock(rtnl_mutex);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

1 lock held by syz-executor7/3877:
 #0:  (rtnl_mutex){+.+.}, at: [<000000008c5736ae>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:74

stack backtrace:
CPU: 1 PID: 3877 Comm: syz-executor7 Not tainted 4.15.0-rc2-mm1+ #39
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+0x194/0x257 lib/dump_stack.c:53
 print_deadlock_bug kernel/locking/lockdep.c:1809 [inline]
 check_deadlock kernel/locking/lockdep.c:1856 [inline]
 validate_chain kernel/locking/lockdep.c:2457 [inline]
 __lock_acquire+0x11cf/0x47f0 kernel/locking/lockdep.c:3500
 lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4004
 __mutex_lock_common kernel/locking/mutex.c:756 [inline]
 __mutex_lock+0x16f/0x1a80 kernel/locking/mutex.c:893
 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
 rtnl_lock+0x17/0x20 net/core/rtnetlink.c:74
 tun_free_netdev+0x158/0x1f0 drivers/net/tun.c:2068
 register_netdevice+0x97b/0x1010 net/core/dev.c:7774
 tun_set_iff drivers/net/tun.c:2389 [inline]
 __tun_chr_ioctl+0x1ca3/0x3f10 drivers/net/tun.c:2613
 tun_chr_ioctl+0x2a/0x40 drivers/net/tun.c:2866
 vfs_ioctl fs/ioctl.c:46 [inline]
 do_vfs_ioctl+0x1b1/0x1530 fs/ioctl.c:686
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
 entry_SYSCALL_64_fastpath+0x1f/0x96
RIP: 0033:0x452a09
RSP: 002b:00007eff6dae7c58 EFLAGS: 00000212 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 000000000071bf58 RCX: 0000000000452a09
RDX: 0000000020533000 RSI: 00000000400454ca RDI: 0000000000000015
RBP: 00000000000003f2 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f2f50
R13: 00000000ffffffff R14: 00007eff6dae86d4 R15: 0000000000000001
kauditd_printk_skb: 386 callbacks suppressed
audit: type=1400 audit(1513583171.350:404): avc:  denied  { bind } for  pid=3926 comm="syz-executor5" scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=netlink_generic_socket permissive=1
could not allocate digest TFM handle wp2ùQˆ