tick/nohz: unexport __init-annotated tick_nohz_full_setup()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: tick/nohz: unexport __init-annotated tick_nohz_full_setup() 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 had been broken for a decade. Commit 28438794aba4 ("modpost: fix section mismatch check for exported init/exit sections") fixed it so modpost started to warn it again, then this showed up: MODPOST vmlinux.symvers WARNING: modpost: vmlinux.o(___ksymtab_gpl+tick_nohz_full_setup+0x0): Section mismatch in reference from the variable __ksymtab_tick_nohz_full_setup to the function .init.text:tick_nohz_full_setup() The symbol tick_nohz_full_setup is exported and annotated __init Fix this by removing the __init annotation of tick_nohz_full_setup or drop the export. Drop the export because tick_nohz_full_setup() is only called from the built-in code in kernel/sched/isolation.c.

References

• https://git.kernel.org/stable/c/c4ff3ffe0138234774602152fe67e3a898c615c6
• https://git.kernel.org/stable/c/f4a80ec8c51d68be4b7a7830c510f75080c5e417
• https://git.kernel.org/stable/c/ea32b27e2f8c58c92bff5ecba7fcf64b97707089
• https://git.kernel.org/stable/c/2390095113e98fc52fffe35c5206d30d9efe3f78