CVE-2022-48817

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

net: dsa: ar9331: register the mdiobus under devres

As explained in commits: 74b6d7d13307 (net: dsa: realtek: register the MDIO bus under devres) 5135e96a3dd2 (net: dsa: dont 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 ar9331 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 ar9331 switch driver on shutdown.

So the same treatment must be applied to all DSA switch drivers, which is: either use devres for both the mdiobus allocation and registration, or dont use devres at all.

The ar9331 driver doesnt have a complex code structure for mdiobus removal, so just replace of_mdiobus_register with the devres variant in order to be all-devres and ensure that we dont free a still-registered bus.

Affected Software

References

• https://git.kernel.org/stable/c/475ce5dcf2d88fd4f3c213a0ac944e3e40702970
• https://git.kernel.org/stable/c/50facd86e9fbc4b93fe02e5fe05776047f45dbfb
• https://git.kernel.org/stable/c/aae1c6a1d3d696fc33b609fb12fe744a556d1dc5
• https://git.kernel.org/stable/c/f1842a8cb71de4d7eb75a86f76e88c7ee739218c