CVE-2026-99285: netfilter: nft_byteorder: remove multi-register support

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

netfilter: nftbyteorder: remove multi-register support

64bit byteorder conversion is broken when several registers need to be converted because the source register array advances in steps for 4 bytes instead of 8:

for (i = ... src64 = nftregload64(&src[i]); ~~~~~ u32 src nftregstore64(&dst64[i],

Remove the multi-register support, it has other issues as well:

Pablo points out that commit caf3ef7468f7 ("netfilter: nftables: prevent OOB access in nftbyteordereval") alters semantics: before the loop operated on registers, i.e. for ( ... ) dst32[i] = htons((u16)src32[i])

.. but after the patch it will operate on bytes, which makes this useless to convert e.g. concatenations, which store each compound in its own register.

Multi-convert of u32 has one theoretical application:

ct mark . meta mark . tcp dport @intervalset

Because ct mark and meta mark are host byte order, use with intervals has to convert the byteorder for ct/meta mark value to network byte order (bigendian).

nftables emits this: [ meta load mark => reg 1 ] [ byteorder reg 1 = hton(reg 1, 4, 4) ] [ ct load mark => reg 9 ] [ byteorder reg 9 = hton(reg 9, 4, 4) ] ...

I.e. two separate calls. Theoretically it could be changed to do: [ meta load mark => reg 1 ] [ ct load mark => reg 9 ] [ byteorder reg 1 = htonl(reg 1, 4, 8) ] ...

But then all it would take to change the set to meta mark . tcp dport . ct mark

... and we'd be back to two "byteorder" calls. IOW, support to convert a range of registers is both dysfunctional and dubious.

Simplify this: remove the feature.

Pablo Neira Ayuso points out that nftables before 1.1.0 can generate incorrect byteorder conversions, see 9fe58952c45a, "evaluate: skip byteorder conversion for selector smaller than 2 bytes" in nftables.git). Affected rulesets fail to load with this change and old userspace due to 'len != size' check.