CVE-2026-99285
netfilter: nft_byteorder: remove multi-register support
In the Linux kernel, the following vulnerability has been resolved:
netfilter: nft_byteorder: 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 = nft_reg_load64(&src[i]);
~~~~~ u32 *src
nft_reg_store64(&dst64[i],
Remove the multi-register support, it has other issues as well:
Pablo points out that commit
caf3ef7468f7 ("netfilter: nf_tables: prevent OOB access in nft_byteorder_eval")
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.
