linux-cve-announce - CVE-2025-71097: ipv4: Fix reference count leak when using error routes with nexthop objects

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Message-ID: <2026011344-CVE-2025-71097-7cfc@gregkh>
Date: Tue, 13 Jan 2026 16:35:56 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-71097: ipv4: Fix reference count leak when using error routes with nexthop objects

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

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

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

ipv4: Fix reference count leak when using error routes with nexthop objects

When a nexthop object is deleted, it is marked as dead and then
fib_table_flush() is called to flush all the routes that are using the
dead nexthop.

The current logic in fib_table_flush() is to only flush error routes
(e.g., blackhole) when it is called as part of network namespace
dismantle (i.e., with flush_all=true). Therefore, error routes are not
flushed when their nexthop object is deleted:

 # ip link add name dummy1 up type dummy
 # ip nexthop add id 1 dev dummy1
 # ip route add 198.51.100.1/32 nhid 1
 # ip route add blackhole 198.51.100.2/32 nhid 1
 # ip nexthop del id 1
 # ip route show
 blackhole 198.51.100.2 nhid 1 dev dummy1

As such, they keep holding a reference on the nexthop object which in
turn holds a reference on the nexthop device, resulting in a reference
count leak:

 # ip link del dev dummy1
 [   70.516258] unregister_netdevice: waiting for dummy1 to become free. Usage count = 2

Fix by flushing error routes when their nexthop is marked as dead.

IPv6 does not suffer from this problem.

The Linux kernel CVE team has assigned CVE-2025-71097 to this issue.


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

	Issue introduced in 5.3 with commit 493ced1ac47c48bb86d9d4e8e87df8592be85a0e and fixed in 6.1.160 with commit 30386e090c49e803c0616a7147e43409c32a2b0e
	Issue introduced in 5.3 with commit 493ced1ac47c48bb86d9d4e8e87df8592be85a0e and fixed in 6.6.120 with commit 5979338c83012110ccd45cae6517591770bfe536
	Issue introduced in 5.3 with commit 493ced1ac47c48bb86d9d4e8e87df8592be85a0e and fixed in 6.12.64 with commit ee4183501ea556dca31f5ffd8690aa9fd25b609f
	Issue introduced in 5.3 with commit 493ced1ac47c48bb86d9d4e8e87df8592be85a0e and fixed in 6.18.4 with commit e3fc381320d04e4a74311e576a86cac49a16fc43
	Issue introduced in 5.3 with commit 493ced1ac47c48bb86d9d4e8e87df8592be85a0e and fixed in 6.19-rc4 with commit ac782f4e3bfcde145b8a7f8af31d9422d94d172a

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-2025-71097
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/ipv4/fib_trie.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/30386e090c49e803c0616a7147e43409c32a2b0e
	https://git.kernel.org/stable/c/5979338c83012110ccd45cae6517591770bfe536
	https://git.kernel.org/stable/c/ee4183501ea556dca31f5ffd8690aa9fd25b609f
	https://git.kernel.org/stable/c/e3fc381320d04e4a74311e576a86cac49a16fc43
	https://git.kernel.org/stable/c/ac782f4e3bfcde145b8a7f8af31d9422d94d172a