linux-cve-announce - CVE-2025-38732: netfilter: nf_reject: don't leak dst refcount for loopback packets

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Message-ID: <2025090543-CVE-2025-38732-f9e4@gregkh>
Date: Fri,  5 Sep 2025 19:20:41 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38732: netfilter: nf_reject: don't leak dst refcount for loopback packets

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

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

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

netfilter: nf_reject: don't leak dst refcount for loopback packets

recent patches to add a WARN() when replacing skb dst entry found an
old bug:

WARNING: include/linux/skbuff.h:1165 skb_dst_check_unset include/linux/skbuff.h:1164 [inline]
WARNING: include/linux/skbuff.h:1165 skb_dst_set include/linux/skbuff.h:1210 [inline]
WARNING: include/linux/skbuff.h:1165 nf_reject_fill_skb_dst+0x2a4/0x330 net/ipv4/netfilter/nf_reject_ipv4.c:234
[..]
Call Trace:
 nf_send_unreach+0x17b/0x6e0 net/ipv4/netfilter/nf_reject_ipv4.c:325
 nft_reject_inet_eval+0x4bc/0x690 net/netfilter/nft_reject_inet.c:27
 expr_call_ops_eval net/netfilter/nf_tables_core.c:237 [inline]
 ..

This is because blamed commit forgot about loopback packets.
Such packets already have a dst_entry attached, even at PRE_ROUTING stage.

Instead of checking hook just check if the skb already has a route
attached to it.

The Linux kernel CVE team has assigned CVE-2025-38732 to this issue.


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

	Issue introduced in 5.9 with commit f53b9b0bdc59c0823679f2e3214e0d538f5951b9 and fixed in 5.10.241 with commit 7b8b503c06274ef3c6c1a107743f1ec0d0a53ef8
	Issue introduced in 5.9 with commit f53b9b0bdc59c0823679f2e3214e0d538f5951b9 and fixed in 5.15.190 with commit 82ef97abf22790182f7d433c74960dfd61b99c33
	Issue introduced in 5.9 with commit f53b9b0bdc59c0823679f2e3214e0d538f5951b9 and fixed in 6.1.149 with commit b7a885ba25960c91db237c3f83b4285156789bce
	Issue introduced in 5.9 with commit f53b9b0bdc59c0823679f2e3214e0d538f5951b9 and fixed in 6.6.103 with commit a0a3ace2a57887dac1e7c9a724846040c3e31868
	Issue introduced in 5.9 with commit f53b9b0bdc59c0823679f2e3214e0d538f5951b9 and fixed in 6.12.44 with commit 51e8531371f90bee742c63775c9a568e5d6bf3c5
	Issue introduced in 5.9 with commit f53b9b0bdc59c0823679f2e3214e0d538f5951b9 and fixed in 6.16.4 with commit b32e1590a8d22cf7d7f965e46d5576051acf8e42
	Issue introduced in 5.9 with commit f53b9b0bdc59c0823679f2e3214e0d538f5951b9 and fixed in 6.17-rc3 with commit 91a79b792204313153e1bdbbe5acbfc28903b3a5

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-2025-38732
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/netfilter/nf_reject_ipv4.c
	net/ipv6/netfilter/nf_reject_ipv6.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/7b8b503c06274ef3c6c1a107743f1ec0d0a53ef8
	https://git.kernel.org/stable/c/82ef97abf22790182f7d433c74960dfd61b99c33
	https://git.kernel.org/stable/c/b7a885ba25960c91db237c3f83b4285156789bce
	https://git.kernel.org/stable/c/a0a3ace2a57887dac1e7c9a724846040c3e31868
	https://git.kernel.org/stable/c/51e8531371f90bee742c63775c9a568e5d6bf3c5
	https://git.kernel.org/stable/c/b32e1590a8d22cf7d7f965e46d5576051acf8e42
	https://git.kernel.org/stable/c/91a79b792204313153e1bdbbe5acbfc28903b3a5