In the Linux kernel, the following vulnerability has been resolved:
net: dsa: properly keep track of conduit reference
Problem description
-------------------
DSA has a mumbo-jumbo of reference handling of the conduit net device
and its kobject which, sadly, is just wrong and doesn't make sense.
There are two distinct problems.
- The OF path, which uses of_find_net_device_by_node(), never releases
the elevated refcount on the conduit's kobject. Nominally, the OF and
non-OF paths should result in objects having identical reference
counts taken, and it is already suspicious that
dsa_dev_to_net_device() has a put_device() call which is missing in
dsa_port_parse_of(), but we can actually even verify that an issue
exists. With CONFIG_DEBUG_KOBJECT_RELEASE=y, if we run this command
"before" and "after" applying this patch:
(unbind the conduit driver for net device eno2)
echo 0000:00:00.2 > /sys/bus/pci/drivers/fsl_enetc/unbind
we see these lines in the output diff which appear only with the patch
applied:
kobject: 'eno2' (ffff002009a3a6b8): kobject_release, parent 0000000000000000 (delayed 1000)
kobject: '109' (ffff0020099d59a0): kobject_release, parent 0000000000000000 (delayed 1000)
- After we find the conduit interface one way (OF) or another (non-OF),
it can get unregistered at any time, and DSA remains with a long-lived,
but in this case stale, cpu_dp->conduit pointer. Holding the net
device's underlying kobject isn't actually of much help, it just
prevents it from being freed (but we never need that kobject
directly). What helps us to prevent the net device from being
unregistered is the parallel netdev reference mechanism (dev_hold()
and dev_put()).
Actually we actually use that netdev tracker mechanism implicitly on
user ports since commit 2f1e8ea726e9 ("net: dsa: link interfaces with
the DSA master to get rid of lockdep warnings"), via netdev_upper_dev_link().
But time still passes at DSA switch probe time between the initial
of_find_net_device_by_node() code and the user port creation time, time
during which the conduit could unregister itself and DSA wouldn't know
about it.
So we have to run of_find_net_device_by_node() under rtnl_lock() to
prevent that from happening, and release the lock only with the netdev
tracker having acquired the reference.
Do we need to keep the reference until dsa_unregister_switch() /
dsa_switch_shutdown()?
1: Maybe yes. A switch device will still be registered even if all user
ports failed to probe, see commit 86f8b1c01a0a ("net: dsa: Do not
make user port errors fatal"), and the cpu_dp->conduit pointers
remain valid. I haven't audited all call paths to see whether they
will actually use the conduit in lack of any user port, but if they
do, it seems safer to not rely on user ports for that reference.
- Definitely yes. We support changing the conduit which a user port is
associated to, and we can get into a situation where we've moved all
user ports away from a conduit, thus no longer hold any reference to
it via the net device tracker. But we shouldn't let it go nonetheless
- see the next change in relation to dsa_tree_find_first_conduit()
and LAG conduits which disappear.
We have to be prepared to return to the physical conduit, so the CPU
port must explicitly keep another reference to it. This is also to
say: the user ports and their CPU ports may not always keep a
reference to the same conduit net device, and both are needed.
As for the conduit's kobject for the /sys/class/net/ entry, we don't
care about it, we can release it as soon as we hold the net device
object itself.
History and blame attribution
-----------------------------
The code has been refactored so many times, it is very difficult to
follow and properly attribute a blame, but I'll try to make a short
history which I hope to be correct.
We have two distinct probing paths:
- one for OF, introduced in 2016 i
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What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (7.8): severity, escalated by confirmed exploitation. This CVE's 7.8 is its impact severity (EG Severity), not escalated.
- EG Severity
- 7.8 HIGHCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
- EG Likelihood
- 0.1% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-29). FIRST's exploitation probability, not an EchelonGraph model.
- Confirmed exploitation
- None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- SSVC Track at medium mission impactTrack at low or medium mission impact; Track* at high (mission-essential systems).CISA BOD 26-04: 14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Track* at high (mission-essential systems).
A fix is available. Apply it within your standard update timelines.
Exploitation none (no CISA value, KEV listing or exploit code on record) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). EchelonGraph holds no SSVC assessment of this CVE from CISA: none of these inputs is from Vulnrichment. EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table
BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.
The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). Where an input reads “CISA's BOD 26-04 default”, no one has published it for this CVE, and CISA's implementation guidance says: “If “Automatable” and “Technical Impact” information items about a CVE ID are not available and the CVE ID is not in the KEV Catalog, CISA will treat its values as “no” and “total,” respectively, until CISA or a third party provides metadata about the CVE ID. CISA will always provide the Vulnrichment data for a CVE ID listed in the KEV Catalog.” Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it