net: xfrm: unexport __init-annotated xfrm4_protocol_init()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: net: xfrm: unexport __init-annotated xfrm4_protocol_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, net/ipv4/xfrm4_policy.c is never compiled as modular. (CONFIG_XFRM is boolean)

References

• https://git.kernel.org/stable/c/c58d82a1264813e69119c13e9804e2e60b664ad5
• https://git.kernel.org/stable/c/e53cd3814504b2cadaba4d5a8a07eeea9ddacd03
• https://git.kernel.org/stable/c/31f3c6a4dcd3260a386e62cef2d5b36e902600a1
• https://git.kernel.org/stable/c/ef6d2354de238b065d8799c80da4be9a6af18e39
• https://git.kernel.org/stable/c/be3884d5cd04ccd58294b83a02d70b7c5fca19d3
• https://git.kernel.org/stable/c/85a055c03691e51499123194a14a0c249cf33227
• https://git.kernel.org/stable/c/e04d59cfe0c0129df7aba7ef7bb17b96be2a64f2
• https://git.kernel.org/stable/c/2b253fbc9f7b5db18d716436bdcf8ecef09fd63d
• https://git.kernel.org/stable/c/4a388f08d8784af48f352193d2b72aaf167a57a1