net: mdio: unexport __init-annotated mdio_bus_init()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: net: mdio: unexport __init-annotated mdio_bus_init() EXPORT_SYMBOL and __init is a bad combination because the .init.text section is freed up after the initialization. Hence, modules cannot use symbols annotated __init. The access to a freed symbol may end up with kernel panic. modpost used to detect it, but it has been broken for a decade. Recently, I fixed modpost so it started to warn it again, then this showed up in linux-next builds. There are two ways to fix it: - Remove __init - Remove EXPORT_SYMBOL I chose the latter for this case because the only in-tree call-site, drivers/net/phy/phy_device.c is never compiled as modular. (CONFIG_PHYLIB is boolean)

References

• https://git.kernel.org/stable/c/ab64ec2c75683f30ccde9eaaf0761002f901aa12
• https://git.kernel.org/stable/c/5534bcd7c40299862237c4a8fd9c5031b3db1538
• https://git.kernel.org/stable/c/6a90a44d53428a3bf01bd80df9ba78b19959270c
• https://git.kernel.org/stable/c/7759c3222815b945a94b212bc0c6cdec475cfec2
• https://git.kernel.org/stable/c/59fa94cddf9eef8d8dae587373eed8b8f4eb11d7
• https://git.kernel.org/stable/c/f5c68137f1191ba3fcf6260ec71b30be2e2bf4c3
• https://git.kernel.org/stable/c/f2f0f8c18b60ca64ff50892ed899cf1c77864755
• https://git.kernel.org/stable/c/35b42dce619701f1300fb8498dae82c9bb1f0263