CVE-2026-64079: netfilter: x_tables: allocate hook ops while under mutex

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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

netfilter: x_tables: allocate hook ops while under mutex

arp/ip(6)t_register_table() add the table to the per-netns list via
xt_register_table() before allocating the per-netns hook ops copy
via kmemdup_array().  This leaves a window where the table is
visible in the list with ops=NULL.

If the pernet exit happens runs concurrently the pre_exit callback finds
the table via xt_find_table() and passes the NULL ops pointer to
nf_unregister_net_hooks(), causing a NULL dereference:

  general protection fault in nf_unregister_net_hooks+0xbc/0x150
  RIP: nf_unregister_net_hooks (net/netfilter/core.c:613)
  Call Trace:
    ipt_unregister_table_pre_exit
    iptable_mangle_net_pre_exit
    ops_pre_exit_list
    cleanup_net

Fix by moving the ops allocation into the xtables core so the table is
never in the list without valid ops.  Also ensure the table is no longer
processing packets before its torn down on error unwind.
nf_register_net_hooks might have published at least one hook; call
synchronize_rcu() if there was an error.

audit log register message gets deferred until all operations have
passed, this avoids need to emit another ureg message in case of
error unwinding.

Based on earlier patch by Tristan Madani.

The Linux kernel CVE team has assigned CVE-2026-64079 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 5.13 with commit ae689334225ff0e4ef112459ecd24aea932c2b00 and fixed in 7.0.11 with commit 2f92c5f923979f37ab1d5445381e4b8378a196cc
	Issue introduced in 5.13 with commit ae689334225ff0e4ef112459ecd24aea932c2b00 and fixed in 7.1 with commit b62eb8dcf2c47d4d676a434efbd57c4f776f7829

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-64079
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	include/linux/netfilter/x_tables.h
	net/ipv4/netfilter/arp_tables.c
	net/ipv4/netfilter/ip_tables.c
	net/ipv6/netfilter/ip6_tables.c
	net/netfilter/x_tables.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/2f92c5f923979f37ab1d5445381e4b8378a196cc
	https://git.kernel.org/stable/c/b62eb8dcf2c47d4d676a434efbd57c4f776f7829