SSLSocket#connect eventually calls `GetOpenFile` in order to get the
underlying file descriptor for the IO object passed in on
initialization. `GetOpenFile` assumes that the Ruby object passed in is
a T_FILE object and just casts it to a T_FILE without any checks. If
you pass an object that *isn't* a T_FILE to that function, the program
will segv.
Since we assume the IO object is a file in the `connect` method, this
commit adds a `CheckType` in the initialize method to ensure that the IO
object is actually a T_FILE. If the object *isn't* a T_FILE, this class
will segv on `connect`, so I think this is a backwards compatible
change.
https://github.com/ruby/openssl/commit/919fa44ec2
35b9d8d393