Bug 2555046 (CVE-2026-98796)

Summary:	CVE-2026-98796 kernel: net: ethernet: mtk_eth_soc: allocate dummy netdev sooner
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in the Linux kernel's MediaTek Ethernet driver. This vulnerability allows a local user with network administration privileges to cause a Denial of Service (DoS) through a kernel crash. Due to an ordering issue during device initialization, the network interface is registered and exposed to the operating system before its internal dummy device structures are allocated. Activating the network interface during this timing window leads to a null pointer dereference, crashing the system.	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-10-18 15:51:25 UTC

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

net: ethernet: mtk_eth_soc: allocate dummy netdev sooner

The RX rings and the shared NAPI are carried by an internal "dummy" netdev
(eth->dummy_dev). mtk_probe() creates that dummy device, and adds the
shared tx/rx NAPI to it, only after the MAC netdevs have been registered.
That order has been there since the MT7623 support was added and leaves a
window in which the netdevs are visible to the network core before the
shared NAPI and the dummy device exist.

If anything brings the first netdev up during that window (e.g. netifd
opening the WAN link the instant the interface is registered), the
first-open path runs without them. On NETSYS v2 and later SoCs
mtk_rx_alloc() -> __xdp_rxq_info_reg() then dereferences eth->dummy_dev ==
NULL:

  WARNING: CPU: ... Missing net_device from driver

in net/core/xdp.c and mtk_open() fails with -ENODEV. On NETSYS v1 SoCs
(MT7621/MT7622/MT7623/MT7629) there is no page pool, so the same open
instead calls napi_enable() on a napi_struct that netif_napi_add() has not
initialised yet and dereferences a NULL napi->dev.

Allocate the dummy netdev and add the shared tx/rx NAPI to it before the
register_netdev() loop. Both the dummy-allocation failure and a
register_netdev() failure now unwind through mtk_unreg_dev(), which
unregisters the net_device notifiers and the netdevs registered so far,
stopping a concurrently-opened netdev (ndo_stop) and its NAPI before the
dummy carrier is freed.

A netdev that opened during the window can also have queued the
frame-engine reset worker (via the tx watchdog or phylink), so the probe
error path now cancels eth->pending_work before freeing the shared state,
as mtk_cleanup() already does on remove.