CVE-2022-48812

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

net: dsa: lantiq_gswip: 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 slavemiibus using devres")

mdiobusfree() will panic when called from devmmdiobusfree() <- devresrelease_all() <- __devicereleasedriver(), and that mdiobus was not previously unregistered.

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