tipc: re-fetch skb cb after tipc_msg_validate
In the Linux kernel, the following vulnerability has been resolved:

tipc: re-fetch skb cb after tipc_msg_validate

As the call trace shows, the original skb was freed in tipc_msg_validate(),
and dereferencing the old skb cb would cause an use-after-free crash.

  BUG: KASAN: use-after-free in tipc_crypto_rcv_complete+0x1835/0x2240 [tipc]
  Call Trace:
   <IRQ>
   tipc_crypto_rcv_complete+0x1835/0x2240 [tipc]
   tipc_crypto_rcv+0xd32/0x1ec0 [tipc]
   tipc_rcv+0x744/0x1150 [tipc]
  ...
  Allocated by task 47078:
   kmem_cache_alloc_node+0x158/0x4d0
   __alloc_skb+0x1c1/0x270
   tipc_buf_acquire+0x1e/0xe0 [tipc]
   tipc_msg_create+0x33/0x1c0 [tipc]
   tipc_link_build_proto_msg+0x38a/0x2100 [tipc]
   tipc_link_timeout+0x8b8/0xef0 [tipc]
   tipc_node_timeout+0x2a1/0x960 [tipc]
   call_timer_fn+0x2d/0x1c0
  ...
  Freed by task 47078:
   tipc_msg_validate+0x7b/0x440 [tipc]
   tipc_crypto_rcv_complete+0x4b5/0x2240 [tipc]
   tipc_crypto_rcv+0xd32/0x1ec0 [tipc]
   tipc_rcv+0x744/0x1150 [tipc]

This patch fixes it by re-fetching the skb cb from the new allocated skb
after calling tipc_msg_validate().