CVE-2024-50038

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

netfilter: xtables: avoid NFPROTO_UNSPEC where needed

syzbot managed to call xt_cluster match via ebtables:

WARNING: CPU: 0 PID: 11 at net/netfilter/xt_cluster.c:72 xt_cluster_mt+0x196/0x780
[..]
ebt_do_table+0x174b/0x2a40

Module registers to NFPROTO_UNSPEC, but it assumes ipv4/ipv6 packet
processing. As this is only useful to restrict locally terminating
TCP/UDP traffic, register this for ipv4 and ipv6 family only.

Pablo points out that this is a general issue, direct users of the
set/getsockopt interface can call into targets/matches that were only
intended for use with ip(6)tables.

Check all UNSPEC matches and targets for similar issues:

- matches and targets are fine except if they assume skb_network_header()
is valid -- this is only true when called from inet layer: ip(6) stack
pulls the ip/ipv6 header into linear data area.
- targets that return XT_CONTINUE or other xtables verdicts must be
restricted too, they are incompatbile with the ebtables traverser, e.g.
EBT_CONTINUE is a completely different value than XT_CONTINUE.

Most matches/targets are changed to register for NFPROTO_IPV4/IPV6, as
they are provided for use by ip(6)tables.

The MARK target is also used by arptables, so register for NFPROTO_ARP too.

While at it, bail out if connbytes fails to enable the corresponding
conntrack family.

This change passes the selftests in iptables.git.