linux-cve-announce - CVE-2025-39874: macsec: sync features on RTM

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [day] [month] [year] [list]

Message-ID: <2025092300-CVE-2025-39874-d462@gregkh>
Date: Tue, 23 Sep 2025 08:01:05 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-39874: macsec: sync features on RTM_NEWLINK

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

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

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

macsec: sync features on RTM_NEWLINK

Syzkaller managed to lock the lower device via ETHTOOL_SFEATURES:

 netdev_lock include/linux/netdevice.h:2761 [inline]
 netdev_lock_ops include/net/netdev_lock.h:42 [inline]
 netdev_sync_lower_features net/core/dev.c:10649 [inline]
 __netdev_update_features+0xcb1/0x1be0 net/core/dev.c:10819
 netdev_update_features+0x6d/0xe0 net/core/dev.c:10876
 macsec_notify+0x2f5/0x660 drivers/net/macsec.c:4533
 notifier_call_chain+0x1b3/0x3e0 kernel/notifier.c:85
 call_netdevice_notifiers_extack net/core/dev.c:2267 [inline]
 call_netdevice_notifiers net/core/dev.c:2281 [inline]
 netdev_features_change+0x85/0xc0 net/core/dev.c:1570
 __dev_ethtool net/ethtool/ioctl.c:3469 [inline]
 dev_ethtool+0x1536/0x19b0 net/ethtool/ioctl.c:3502
 dev_ioctl+0x392/0x1150 net/core/dev_ioctl.c:759

It happens because lower features are out of sync with the upper:

  __dev_ethtool (real_dev)
    netdev_lock_ops(real_dev)
    ETHTOOL_SFEATURES
      __netdev_features_change
        netdev_sync_upper_features
          disable LRO on the lower
    if (old_features != dev->features)
      netdev_features_change
        fires NETDEV_FEAT_CHANGE
	macsec_notify
	  NETDEV_FEAT_CHANGE
	    netdev_update_features (for each macsec dev)
	      netdev_sync_lower_features
	        if (upper_features != lower_features)
	          netdev_lock_ops(lower) # lower == real_dev
		  stuck
		  ...

    netdev_unlock_ops(real_dev)

Per commit af5f54b0ef9e ("net: Lock lower level devices when updating
features"), we elide the lock/unlock when the upper and lower features
are synced. Makes sure the lower (real_dev) has proper features after
the macsec link has been created. This makes sure we never hit the
situation where we need to sync upper flags to the lower.

The Linux kernel CVE team has assigned CVE-2025-39874 to this issue.


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

	Issue introduced in 6.15 with commit 7e4d784f5810bba76c4593791028e13cce4af547 and fixed in 6.16.8 with commit d7624629ccf47135c65fef0701fa0d9a115b87f3
	Issue introduced in 6.15 with commit 7e4d784f5810bba76c4593791028e13cce4af547 and fixed in 6.17-rc6 with commit 0f82c3ba66c6b2e3cde0f255156a753b108ee9dc

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-2025-39874
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:
	drivers/net/macsec.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/d7624629ccf47135c65fef0701fa0d9a115b87f3
	https://git.kernel.org/stable/c/0f82c3ba66c6b2e3cde0f255156a753b108ee9dc