Subject: CVE-2024-42109: netfilter: nf_tables: unconditionally flush pending work before notifier

From: Greg Kroah-Hartman <[email-masked]>

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

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

netfilter: nf_tables: unconditionally flush pending work before notifier

syzbot reports:

KASAN: slab-uaf in nft_ctx_update include/net/netfilter/nf_tables.h:1831
KASAN: slab-uaf in nft_commit_release net/netfilter/nf_tables_api.c:9530
KASAN: slab-uaf int nf_tables_trans_destroy_work+0x152b/0x1750 net/netfilter/nf_tables_api.c:9597
Read of size 2 at addr ffff88802b0051c4 by task kworker/1:1/45
[..]
Workqueue: events nf_tables_trans_destroy_work
Call Trace:
 nft_ctx_update include/net/netfilter/nf_tables.h:1831 [inline]
 nft_commit_release net/netfilter/nf_tables_api.c:9530 [inline]
 nf_tables_trans_destroy_work+0x152b/0x1750 net/netfilter/nf_tables_api.c:9597

Problem is that the notifier does a conditional flush, but its possible
that the table-to-be-removed is still referenced by transactions being
processed by the worker, so we need to flush unconditionally.

We could make the flush_work depend on whether we found a table to delete
in nf-next to avoid the flush for most cases.

AFAICS this problem is only exposed in nf-next, with
commit e169285f8c56 ("netfilter: nf_tables: do not store nft_ctx in transaction objects"),
with this commit applied there is an unconditional fetch of
table->family which is whats triggering the above splat.

The Linux kernel CVE team has assigned CVE-2024-42109 to this issue.

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

	Issue introduced in 5.15.129 with commit f22954f8c58f and fixed in 5.15.163 with commit 3325628cb36b
	Issue introduced in 6.1.50 with commit 41841b585e53 and fixed in 6.1.98 with commit 4c06c13317b9
	Issue introduced in 6.5 with commit 2c9f0293280e and fixed in 6.6.39 with commit 55a40406aac5
	Issue introduced in 6.5 with commit 2c9f0293280e and fixed in 6.9.9 with commit 09e650c3a3a7
	Issue introduced in 6.5 with commit 2c9f0293280e and fixed in 6.10 with commit 9f6958ba2e90
	Issue introduced in 6.4.13 with commit 4167aa477abc

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-2024-42109
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:
	net/netfilter/nf_tables_api.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/3325628cb36b7f216c5716e7b5124d9dc81199e4
	https://git.kernel.org/stable/c/4c06c13317b9a08decedcd7aaf706691e336277c
	https://git.kernel.org/stable/c/55a40406aac555defe9bdd0adec9508116ce7cb1
	https://git.kernel.org/stable/c/09e650c3a3a7d804430260510534ccbf71c75b2e
	https://git.kernel.org/stable/c/9f6958ba2e902f9820c594869bd710ba74b7c4c0