CVE-2022-48814 Information

Description

In the Linux kernel the following vulnerability has been resolved:

net: dsa: seville: register the mdiobus under devres

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 Seville VSC9959 switch 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 seville 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 seville driver has a code structure that could accommodate both the mdiobus_unregister and mdiobus_free calls but it has an external dependency upon mscc_miim_setup() from mdio-mscc-miim.c which calls devm_mdiobus_alloc_size() on its behalf. So rather than restructuring that and exporting yet one more symbol mscc_miim_teardown() let’s work with devres and replace of_mdiobus_register with the devres variant. When we use all-devres we can ensure that devres doesn’t free a still-registered bus (it either runs both callbacks or none).

Reference

https://git.kernel.org/stable/c/1d13e7221035947c62800c9d3d99b4ed570e27e7 https://git.kernel.org/stable/c/0e816362d823cd46c666e64d8bffe329ee22f4cc https://git.kernel.org/stable/c/bd488afc3b39e045ba71aab472233f2a78726e7b