CVE-2026-80901

In the Linux kernel, the following vulnerability has been resolved:

ipvs: fix the checksum validations

ip_vs_in_icmp_v6() is missing checksum validation for ICMPv6
packets from clients. In fact, as for TCP/UDP we should
validate the checksum for ICMP packets only when we
mangle the packets on MASQ or on reply for tunnel.

Also, Sashiko points out that handle_response_icmp() being
common for IPv4 and IPv6 is missing the pseudo-header
calculation while validating ICMPv6 messages from real
servers which is a problem if checksum is not validated
by the hardware.

Fix the problems by creating ip_vs_checksum_common_check()
helper and use it for TCP/UDP/ICMP both for IPv4 and IPv6.
Rely on the nf_checksum() for validating the ICMP messages
but use it also for TCP and UDP.

Use correct IP offset for IP_VS_DBG_RL_PKT for TCP/UDP/SCTP.

IPVS packets (TCP/UDP/SCTP/ICMP) do not need checksum
validation on LOCAL_OUT (local clients or local real
servers) and on FORWARD (traffic from servers on LAN).
Do it only on LOCAL_IN, in case nf_checksum() is not
called on PRE_ROUTING.

Also, ip_vs_checksum_complete() can be marked static.