CVE-2022-48815net: dsa: bcm_sf2: don't use devres for mdiobus

Official 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 ("net: dsa: realtek: register the MDIO bus under devres") 5135e96a3dd2 ("net: 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.

Affected packages & fixed versions

Affected products (as reported)

References

• 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