netfilter: conntrack: Avoid nf_ct_helper_hash uses after free

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: netfilter: conntrack: Avoid nf_ct_helper_hash uses after free If nf_conntrack_init_start() fails (for example due to a register_nf_conntrack_bpf() failure), the nf_conntrack_helper_fini() clean-up path frees the nf_ct_helper_hash map. When built with NF_CONNTRACK=y, further netfilter modules (e.g: netfilter_conntrack_ftp) can still be loaded and call nf_conntrack_helpers_register(), independently of whether nf_conntrack initialized correctly. This accesses the nf_ct_helper_hash dangling pointer and causes a uaf, possibly leading to random memory corruption. This patch guards nf_conntrack_helper_register() from accessing a freed or uninitialized nf_ct_helper_hash pointer and fixes possible uses-after-free when loading a conntrack module.

References

• https://git.kernel.org/stable/c/4ee69c91cb8f9ca144bc0861969e5a1a3c6152a7
• https://git.kernel.org/stable/c/00716f25f9697d02a0d9bd622575c7c7321ba3d0
• https://git.kernel.org/stable/c/61c7a5256543ae7d24cd9d21853d514c8632e1e9
• https://git.kernel.org/stable/c/8289d422f5e484efe4a565fe18e862ecd621c175
• https://git.kernel.org/stable/c/6f03ce2f1abcb9f9d0511e3659ca6eb60e39f566
• https://git.kernel.org/stable/c/05561f822f27b9fa88fa5504ddec34bf38833034
• https://git.kernel.org/stable/c/fce5cc7cbd4b92f979bf02c9ec5fb69aaeba92d7
• https://git.kernel.org/stable/c/6eef7a2b933885a17679eb8ed0796ddf0ee5309b