gnu: ruby: Replace with ruby-2.4.3 [fixes CVE-2017-17405].

* gnu/packages/ruby.scm (ruby-2.4.3): New variable.
(ruby)[replacement]: New field.

gnu/packages/ruby.scm

@@ -49,6 +49,7 @@
 (define-public ruby
   (package
     (name "ruby")
+    (replacement ruby-2.4.3)
     (version "2.4.2")
     (source
      (origin
@@ -102,6 +103,26 @@ a focus on simplicity and productivity.")
     (home-page "https://ruby-lang.org")
     (license license:ruby)))
 
+(define-public ruby-2.4.3
+  (package
+    (inherit ruby)
+    (name "ruby")
+    (version "2.4.3")
+    (source
+     (origin
+       (method url-fetch)
+       (uri (string-append "http://cache.ruby-lang.org/pub/ruby/"
+                           (version-major+minor version)
+                           "/ruby-" version ".tar.xz"))
+       (sha256
+        (base32
+         "0l9bv67dgsphk42lmiskhrnh47hbyj6rfg2rcjx22xivpx07srr3"))
+       (modules '((guix build utils)))
+       (snippet `(begin
+                   ;; Remove bundled libffi
+                   (delete-file-recursively "ext/fiddle/libffi-3.2.1")
+                   #t))))))
+
 (define-public ruby-2.3
   (package
     (inherit ruby)