linux-cve-announce - CVE-2022-50000: netfilter: flowtable: fix stuck flows on cleanup due to pending work

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Message-ID: <2025061828-CVE-2022-50000-5753@gregkh>
Date: Wed, 18 Jun 2025 13:01:05 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2022-50000: netfilter: flowtable: fix stuck flows on cleanup due to pending work

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

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

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

netfilter: flowtable: fix stuck flows on cleanup due to pending work

To clear the flow table on flow table free, the following sequence
normally happens in order:

  1) gc_step work is stopped to disable any further stats/del requests.
  2) All flow table entries are set to teardown state.
  3) Run gc_step which will queue HW del work for each flow table entry.
  4) Waiting for the above del work to finish (flush).
  5) Run gc_step again, deleting all entries from the flow table.
  6) Flow table is freed.

But if a flow table entry already has pending HW stats or HW add work
step 3 will not queue HW del work (it will be skipped), step 4 will wait
for the pending add/stats to finish, and step 5 will queue HW del work
which might execute after freeing of the flow table.

To fix the above, this patch flushes the pending work, then it sets the
teardown flag to all flows in the flowtable and it forces a garbage
collector run to queue work to remove the flows from hardware, then it
flushes this new pending work and (finally) it forces another garbage
collector run to remove the entry from the software flowtable.

Stack trace:
[47773.882335] BUG: KASAN: use-after-free in down_read+0x99/0x460
[47773.883634] Write of size 8 at addr ffff888103b45aa8 by task kworker/u20:6/543704
[47773.885634] CPU: 3 PID: 543704 Comm: kworker/u20:6 Not tainted 5.12.0-rc7+ #2
[47773.886745] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009)
[47773.888438] Workqueue: nf_ft_offload_del flow_offload_work_handler [nf_flow_table]
[47773.889727] Call Trace:
[47773.890214]  dump_stack+0xbb/0x107
[47773.890818]  print_address_description.constprop.0+0x18/0x140
[47773.892990]  kasan_report.cold+0x7c/0xd8
[47773.894459]  kasan_check_range+0x145/0x1a0
[47773.895174]  down_read+0x99/0x460
[47773.899706]  nf_flow_offload_tuple+0x24f/0x3c0 [nf_flow_table]
[47773.907137]  flow_offload_work_handler+0x72d/0xbe0 [nf_flow_table]
[47773.913372]  process_one_work+0x8ac/0x14e0
[47773.921325]
[47773.921325] Allocated by task 592159:
[47773.922031]  kasan_save_stack+0x1b/0x40
[47773.922730]  __kasan_kmalloc+0x7a/0x90
[47773.923411]  tcf_ct_flow_table_get+0x3cb/0x1230 [act_ct]
[47773.924363]  tcf_ct_init+0x71c/0x1156 [act_ct]
[47773.925207]  tcf_action_init_1+0x45b/0x700
[47773.925987]  tcf_action_init+0x453/0x6b0
[47773.926692]  tcf_exts_validate+0x3d0/0x600
[47773.927419]  fl_change+0x757/0x4a51 [cls_flower]
[47773.928227]  tc_new_tfilter+0x89a/0x2070
[47773.936652]
[47773.936652] Freed by task 543704:
[47773.937303]  kasan_save_stack+0x1b/0x40
[47773.938039]  kasan_set_track+0x1c/0x30
[47773.938731]  kasan_set_free_info+0x20/0x30
[47773.939467]  __kasan_slab_free+0xe7/0x120
[47773.940194]  slab_free_freelist_hook+0x86/0x190
[47773.941038]  kfree+0xce/0x3a0
[47773.941644]  tcf_ct_flow_table_cleanup_work

Original patch description and stack trace by Paul Blakey.

The Linux kernel CVE team has assigned CVE-2022-50000 to this issue.


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

	Issue introduced in 5.5 with commit c29f74e0df7a02b8303bcdce93a7c0132d62577a and fixed in 5.15.64 with commit 8fbdec08dbf7d7ab8e35bdc65eb4394bc82d1e26
	Issue introduced in 5.5 with commit c29f74e0df7a02b8303bcdce93a7c0132d62577a and fixed in 5.19.6 with commit 89e135a36a9eb81412b5459df94a80995ce62eef
	Issue introduced in 5.5 with commit c29f74e0df7a02b8303bcdce93a7c0132d62577a and fixed in 6.0 with commit 9afb4b27349a499483ae0134282cefd0c90f480f

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-2022-50000
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/net/netfilter/nf_flow_table.h
	net/netfilter/nf_flow_table_core.c
	net/netfilter/nf_flow_table_offload.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/8fbdec08dbf7d7ab8e35bdc65eb4394bc82d1e26
	https://git.kernel.org/stable/c/89e135a36a9eb81412b5459df94a80995ce62eef
	https://git.kernel.org/stable/c/9afb4b27349a499483ae0134282cefd0c90f480f