sysctl: Fix out of bounds access for empty sysctl registers

In the Linux kernel, the following vulnerability has been resolved:

sysctl: Fix out of bounds access for empty sysctl registers

When registering tables to the sysctl subsystem there is a check to see

if header is a permanently empty directory (used for mounts). This check

evaluates the first element of the ctl_table. This results in an out of

bounds evaluation when registering empty directories.

The function register_sysctl_mount_point now passes a ctl_table of size

1 instead of size 0. It now relies solely on the type to identify

a permanently empty register.

Make sure that the ctl_table has at least one element before testing for

permanent emptiness.