Restrict broken mime parsing

This commit restricts broken mime parsing to deal with a ReDOS
vulnerability.

[CVE-2022-30122]

lib/rack/multipart.rb

@@ -16,8 +16,7 @@ module Multipart
     TOKEN = /[^\s()<>,;:\\"\/\[\]?=]+/
     CONDISP = /Content-Disposition:\s*#{TOKEN}\s*/i
     VALUE = /"(?:\\"|[^"])*"|#{TOKEN}/
-    BROKEN_QUOTED = /^#{CONDISP}.*;\s*filename="(.*?)"(?:\s*$|\s*;\s*#{TOKEN}=)/i
-    BROKEN_UNQUOTED = /^#{CONDISP}.*;\s*filename=(#{TOKEN})/i
+    BROKEN = /^#{CONDISP}.*;\s*filename=(#{VALUE})/i
     MULTIPART_CONTENT_TYPE = /Content-Type: (.*)#{EOL}/ni
     MULTIPART_CONTENT_DISPOSITION = /Content-Disposition:.*;\s*name=(#{VALUE})/ni
     MULTIPART_CONTENT_ID = /Content-ID:\s*([^#{EOL}]*)/ni

lib/rack/multipart/parser.rb

@@ -309,8 +309,9 @@ def get_filename(head)
           elsif filename = params['filename*']
             encoding, _, filename = filename.split("'", 3)
           end
-        when BROKEN_QUOTED, BROKEN_UNQUOTED
+        when BROKEN
           filename = $1
+          filename = $1 if filename =~ /^"(.*)"$/
         end
 
         return unless filename

test/multipart/filename_with_escaped_quotes_and_modification_param

@@ -1,6 +1,6 @@
 --AaB03x
 Content-Type: image/jpeg
-Content-Disposition: attachment; name="files"; filename=""human" genome.jpeg"; modification-date="Wed, 12 Feb 1997 16:29:51 -0500";
+Content-Disposition: attachment; name="files"; filename="\"human\" genome.jpeg"; modification-date="Wed, 12 Feb 1997 16:29:51 -0500";
 Content-Description: a complete map of the human genome
 
 contents

test/spec_multipart.rb

@@ -421,19 +421,6 @@ def initialize(*)
     params["files"][:tempfile].read.must_equal "contents"
   end
 
-  it "parse filename with unescaped quotes" do
-    env = Rack::MockRequest.env_for("/", multipart_fixture(:filename_with_unescaped_quotes))
-    params = Rack::Multipart.parse_multipart(env)
-    params["files"][:type].must_equal "application/octet-stream"
-    params["files"][:filename].must_equal "escape \"quotes"
-    params["files"][:head].must_equal "Content-Disposition: form-data; " +
-      "name=\"files\"; " +
-      "filename=\"escape \"quotes\"\r\n" +
-      "Content-Type: application/octet-stream\r\n"
-    params["files"][:name].must_equal "files"
-    params["files"][:tempfile].read.must_equal "contents"
-  end
-
   it "parse filename with escaped quotes and modification param" do
     env = Rack::MockRequest.env_for("/", multipart_fixture(:filename_with_escaped_quotes_and_modification_param))
     params = Rack::Multipart.parse_multipart(env)
@@ -442,7 +429,7 @@ def initialize(*)
     params["files"][:head].must_equal "Content-Type: image/jpeg\r\n" +
       "Content-Disposition: attachment; " +
       "name=\"files\"; " +
-      "filename=\"\"human\" genome.jpeg\"; " +
+      "filename=\"\\\"human\\\" genome.jpeg\"; " +
       "modification-date=\"Wed, 12 Feb 1997 16:29:51 -0500\";\r\n" +
       "Content-Description: a complete map of the human genome\r\n"
     params["files"][:name].must_equal "files"