In the Linux kernel, the following vulnerability has been resolved:
tunnels: load network headers after skb_cow() in iptunnel_pmtud_build_icmp[v6]()
Sashiko found that iptunnel_pmtud_build_icmp() and
iptunnel_pmtud_build_icmpv6() were caching ip_hdr() and ipv6_hdr()
before an skb_cow() call which can reallocate skb->head.
Fix this possible UAF by initializing the local variables
after the skb_cow() call.
Remove skb_reset_network_header() calls which were not needed.
