Affected: Linux

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

net: dsa: mv88e6xxx: don't use devres for mdiobus

As explained in commits: 74b6d7d13307 ("net: dsa: realtek: register the MDIO bus under devres") 5135e96a3dd2 ("net: dsa: don't allocate the slave_mii_bus using devres")

mdiobus_free() will panic when called from devm_mdiobus_free() <- devres_release_all() <- __device_release_driver(), and that mdiobus was not previously unregistered.

The mv88e6xxx is an MDIO device, so the initial set of constraints that I thought would cause this (I2C or SPI buses which call ->remove on ->shutdown) do not apply. But there is one more which applies here.

If the DSA master itself is on a bus that calls ->remove from ->shutdown (like dpaa2-eth, which is on the fsl-mc bus), there is a device link between the switch and the DSA master, and device_links_unbind_consumers() will unbind the Marvell switch driver on shutdown.

systemd-shutdown[1]: Powering off. mv88e6085 0x0000000008b96000:00 sw_gl0: Link is Down fsl-mc dpbp.9: Removing from iommu group 7 fsl-mc dpbp.8: Removing from iommu group 7 ------------[ cut here ]------------ kernel BUG at drivers/net/phy/mdio_bus.c:677! Internal error: Oops - BUG: 0 [#1] PREEMPT SMP Modules linked in: CPU: 0 PID: 1 Comm: systemd-shutdow Not tainted 5.16.5-00040-gdc05f73788e5 #15 pc : mdiobus_free+0x44/0x50 lr : devm_mdiobus_free+0x10/0x20 Call trace: mdiobus_free+0x44/0x50 devm_mdiobus_free+0x10/0x20 devres_release_all+0xa0/0x100 __d…