CVE-2022-48815 Information

Description

In the Linux kernel the following vulnerability has been resolved:

net: dsa: bcm_sf2: don’t use devres for mdiobus

As explained in commits: 74b6d7d13307 ( et: dsa: realtek: register the MDIO bus under devres) 5135e96a3dd2 ( et: 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 Starfighter 2 is a platform 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 bcm_sf2 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 don’t use devres at all.

The bcm_sf2 driver has the code structure in place for orderly mdiobus removal so just replace devm_mdiobus_alloc() with the non-devres variant and add manual free where necessary to ensure that we don’t let devres free a still-registered bus.

Reference

https://git.kernel.org/stable/c/2770b795294ed312375c11ef1d0b810499c66b83 https://git.kernel.org/stable/c/caabb5f64f5c32fceed93356bb688ef1ec6c5783 https://git.kernel.org/stable/c/08e1a3554e99a1a5bd2835907381e2383ee85cae https://git.kernel.org/stable/c/08f1a20822349004bb9cc1b153ecb516e9f2889d