net: dsa: mv88e6xxx: avoid unregistering devlink regions which were never registered

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: net: dsa: mv88e6xxx: avoid unregistering devlink regions which were never registered Russell King reports that a system with mv88e6xxx dereferences a NULL pointer when unbinding this driver: https://lore.kernel.org/netdev/Z_lRkMlTJ1KQ0kVX@shell.armlinux.org.uk/ The crash seems to be in devlink_region_destroy(), which is not NULL tolerant but is given a NULL devlink global region pointer. At least on some chips, some devlink regions are conditionally registered since the blamed commit, see mv88e6xxx_setup_devlink_regions_global(): if (cond && !cond(chip)) continue; These are MV88E6XXX_REGION_STU and MV88E6XXX_REGION_PVT. If the chip does not have an STU or PVT, it should crash like this. To fix the issue, avoid unregistering those regions which are NULL, i.e. were skipped at mv88e6xxx_setup_devlink_regions_global() time.

References

• https://git.kernel.org/stable/c/8ccdf5e24b276848eefb2755e05ff0f005a0c4a1
• https://git.kernel.org/stable/c/b3c70dfe51f10df60db2646c08cebd24bcdc5247
• https://git.kernel.org/stable/c/bbb80f004f7a90c3dcaacc982c59967457254a05
• https://git.kernel.org/stable/c/3665695e3572239dc233216f06b41f40cc771889
• https://git.kernel.org/stable/c/5f5e95945bb1e08be7655da6acba648274db457d
• https://git.kernel.org/stable/c/c84f6ce918a9e6f4996597cbc62536bbf2247c96