Merge branch 'net-fix-quite-a-few-dst_cache-crashes-reported-by-syzbot'

Xin Long says:

====================
net: fix quite a few dst_cache crashes reported by syzbot

There are two kinds of crashes reported many times by syzbot with no
reproducer. Call Traces are like:

     BUG: KASAN: slab-out-of-bounds in rt_cache_valid+0x158/0x190
     net/ipv4/route.c:1556
       rt_cache_valid+0x158/0x190 net/ipv4/route.c:1556
       __mkroute_output net/ipv4/route.c:2332 [inline]
       ip_route_output_key_hash_rcu+0x819/0x2d50 net/ipv4/route.c:2564
       ip_route_output_key_hash+0x1ef/0x360 net/ipv4/route.c:2393
       __ip_route_output_key include/net/route.h:125 [inline]
       ip_route_output_flow+0x28/0xc0 net/ipv4/route.c:2651
       ip_route_output_key include/net/route.h:135 [inline]
     ...

   or:

     kasan: GPF could be caused by NULL-ptr deref or user memory access
     RIP: 0010:dst_dev_put+0x24/0x290 net/core/dst.c:168
       <IRQ>
       rt_fibinfo_free_cpus net/ipv4/fib_semantics.c:200 [inline]
       free_fib_info_rcu+0x2e1/0x490 net/ipv4/fib_semantics.c:217
       __rcu_reclaim kernel/rcu/rcu.h:240 [inline]
       rcu_do_batch kernel/rcu/tree.c:2437 [inline]
       invoke_rcu_callbacks kernel/rcu/tree.c:2716 [inline]
       rcu_process_callbacks+0x100a/0x1ac0 kernel/rcu/tree.c:2697
     ...

They were caused by the fib_nh_common percpu member 'nhc_pcpu_rth_output'
overwritten by another percpu variable 'dev->tstats' access overflow in
tipc udp media xmit path when counting packets on a non tunnel device.

The fix is to make udp tunnel work with no tunnel device by allowing not
to count packets on the tstats when the tunnel dev is NULL in Patches 1/3
and 2/3, then pass a NULL tunnel dev in tipc_udp_tunnel() in Patch 3/3.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>