syzbot

netlink: 8 bytes leftover after parsing attributes in process `syz-executor966'.
===============================
[ INFO: suspicious RCU usage. ]
4.9.141+ #1 Not tainted
-------------------------------
net/ipv6/ip6_fib.c:1471 suspicious rcu_dereference_protected() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 0
4 locks held by syz-executor966/2056:
 #0:  (rtnl_mutex){+.+.+.}, at: [<ffffffff823412d7>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
 #1:  (&(&net->ipv6.fib6_gc_lock)->rlock){+.-...}, at: [<ffffffff826ef796>] spin_trylock_bh include/linux/spinlock.h:367 [inline]
 #1:  (&(&net->ipv6.fib6_gc_lock)->rlock){+.-...}, at: [<ffffffff826ef796>] fib6_run_gc+0x226/0x2c0 net/ipv6/ip6_fib.c:1817
 #2:  (rcu_read_lock){......}, at: [<ffffffff826e6c70>] __fib6_clean_all+0x0/0x220 net/ipv6/ip6_fib.c:1703
 #3:  (&tb->tb6_lock){++-...}, at: [<ffffffff826e6d50>] __fib6_clean_all+0xe0/0x220 net/ipv6/ip6_fib.c:1717

stack backtrace:
CPU: 0 PID: 2056 Comm: syz-executor966 Not tainted 4.9.141+ #1
 ffff8801ce99f448 ffffffff81b42e79 ffff8801cfc417c0 0000000000000000
 0000000000000002 ffffffff82cc2480 ffffed0039d33ed7 ffff8801ce99f478
 ffffffff813fe948 ffff8801d65b28c0 ffff8801ce99f668 ffff8801d65b28c0
Call Trace:
 [<ffffffff81b42e79>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81b42e79>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff813fe948>] lockdep_rcu_suspicious.cold.32+0x110/0x141 kernel/locking/lockdep.c:4455
 [<ffffffff826eed80>] fib6_del+0x810/0xb10 net/ipv6/ip6_fib.c:1470
 [<ffffffff826ef2a0>] fib6_clean_node+0x220/0x4c0 net/ipv6/ip6_fib.c:1657
 [<ffffffff826e6545>] fib6_walk_continue+0x3e5/0x640 net/ipv6/ip6_fib.c:1583
 [<ffffffff826e6b01>] fib6_walk+0x91/0xf0 net/ipv6/ip6_fib.c:1628
 [<ffffffff826e6c33>] fib6_clean_tree+0xd3/0x110 net/ipv6/ip6_fib.c:1702
 [<ffffffff826e6d69>] __fib6_clean_all+0xf9/0x220 net/ipv6/ip6_fib.c:1718
 [<ffffffff826ef687>] fib6_clean_all net/ipv6/ip6_fib.c:1729 [inline]
 [<ffffffff826ef687>] fib6_run_gc+0x117/0x2c0 net/ipv6/ip6_fib.c:1826
 [<ffffffff826fa99c>] ndisc_netdev_event+0x2ac/0x350 net/ipv6/ndisc.c:1750
 [<ffffffff811478d4>] notifier_call_chain+0xb4/0x1d0 kernel/notifier.c:93
 [<ffffffff81147a5d>] __raw_notifier_call_chain kernel/notifier.c:394 [inline]
 [<ffffffff81147a5d>] raw_notifier_call_chain+0x2d/0x40 kernel/notifier.c:401
 [<ffffffff822f4a45>] call_netdevice_notifiers_info+0x55/0x70 net/core/dev.c:1647
 [<ffffffff822f5764>] call_netdevice_notifiers net/core/dev.c:1663 [inline]
 [<ffffffff822f5764>] dev_close_many+0x2e4/0x6a0 net/core/dev.c:1456
 [<ffffffff823031ac>] rollback_registered_many+0x3ac/0xb50 net/core/dev.c:6838
 [<ffffffff82303a3e>] rollback_registered+0xee/0x1b0 net/core/dev.c:6901
 [<ffffffff8230d5fa>] unregister_netdevice_queue+0x1aa/0x230 net/core/dev.c:7888
 [<ffffffff81ed1e91>] unregister_netdevice include/linux/netdevice.h:2465 [inline]
 [<ffffffff81ed1e91>] __tun_detach+0x821/0xa00 drivers/net/tun.c:575
 [<ffffffff81ed20b4>] tun_detach drivers/net/tun.c:585 [inline]
 [<ffffffff81ed20b4>] tun_chr_close+0x44/0x60 drivers/net/tun.c:2392
 [<ffffffff81510293>] __fput+0x263/0x700 fs/file_table.c:208
 [<ffffffff815107b5>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8113dc4c>] task_work_run+0x10c/0x180 kernel/task_work.c:116
 [<ffffffff810e6c4d>] exit_task_work include/linux/task_work.h:21 [inline]
 [<ffffffff810e6c4d>] do_exit+0x78d/0x2a50 kernel/exit.c:833
 [<ffffffff810ed3a1>] do_group_exit+0x111/0x300 kernel/exit.c:937
 [<ffffffff810ed5ad>] SYSC_exit_group kernel/exit.c:948 [inline]
 [<ffffffff810ed5ad>] SyS_exit_group+0x1d/0x20 kernel/exit.c:946
 [<ffffffff810056ef>] do_syscall_64+0x19f/0x550 arch/x86/entry/common.c:285
 [<ffffffff82817893>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb