fix possible UAF in icmpv6_rcv()

Summary

In the Linux kernel, the following vulnerability has been resolved: ipv6: fix possible UAF in icmpv6_rcv() Caching saddr and daddr before pskb_pull() is problematic since skb->head can change. Remove these temporary variables: - We only access &ipv6_hdr(skb)->saddr and &ipv6_hdr(skb)->daddr when net_dbg_ratelimited() is called in the slow path. - Avoid potential future misuse after pskb_pull() call. A flaw was found in the Linux kernel's IPv6 (Internet Protocol version 6) implementation. This vulnerability, a Use-After-Free (UAF) error, occurs due to incorrect caching of network packet addresses before a memory operation. An attacker could potentially exploit this flaw to cause memory corruption, which may lead to a denial of service or, in some scenarios, arbitrary code execution. Red Hat severity: Important — CVSS 7 (CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H). Weakness: CWE-825. No fixing RHSA erratum has published yet; monitor the Red Hat CVE page and patch when it ships.