CVE-2022-48814

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

net: dsa: seville: register the mdiobus under devres

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

mdiobusfree() will panic when called from devmmdiobusfree() <- devresrelease_all() <- __devicereleasedriver(), 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 devicelinksunbind_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 mdiobusunregister and mdiobusfree calls, but it has an external dependency upon msccmiimsetup() from mdio-mscc-miim.c, which calls devmmdiobusallocsize() on its behalf. So rather than restructuring that, and exporting yet one more symbol msccmiimteardown(), let's work with devres and replace ofmdiobus_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).