ipvs: Defer ip_vs_ftp unregister during netns cleanup

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: ipvs: Defer ip_vs_ftp unregister during netns cleanup On the netns cleanup path, __ip_vs_ftp_exit() may unregister ip_vs_ftp before connections with valid cp->app pointers are flushed, leading to a use-after-free. Fix this by introducing a global `exiting_module` flag, set to true in ip_vs_ftp_exit() before unregistering the pernet subsystem. In __ip_vs_ftp_exit(), skip ip_vs_ftp unregister if called during netns cleanup (when exiting_module is false) and defer it to __ip_vs_cleanup_batch(), which unregisters all apps after all connections are flushed. If called during module exit, unregister ip_vs_ftp immediately.

References

• https://git.kernel.org/stable/c/8a6ecab3847c213ce2855b0378e63ce839085de3
• https://git.kernel.org/stable/c/421b1ae1574dfdda68b835c15ac4921ec0030182
• https://git.kernel.org/stable/c/1d79471414d7b9424d699afff2aa79fff322f52d
• https://git.kernel.org/stable/c/53717f8a4347b78eac6488072ad8e5adbaff38d9
• https://git.kernel.org/stable/c/8cbe2a21d85727b66d7c591fd5d83df0d8c4f757
• https://git.kernel.org/stable/c/dc1a481359a72ee7e548f1f5da671282a7c13b8f
• https://git.kernel.org/stable/c/a343811ef138a265407167294275201621e9ebb2
• https://git.kernel.org/stable/c/134121bfd99a06d44ef5ba15a9beb075297c0821