ssl: prevent SSLSocket#sysread* from leaking uninitialized data

Set the length of the buffer string to 0 first, and adjust to the size
successfully read by the SSL_read() call later. This is needed because
the buffer string may be provided by the caller.

Author: rhenium

ext/openssl/ossl_ssl.c

@@ -1688,20 +1688,26 @@ ossl_ssl_read_internal(int argc, VALUE *argv, VALUE self, int nonblock)
     }
 
     ilen = NUM2INT(len);
-    if(NIL_P(str)) str = rb_str_new(0, ilen);
-    else{
-        StringValue(str);
-        rb_str_modify(str);
-        rb_str_resize(str, ilen);
+    if (NIL_P(str))
+	str = rb_str_new(0, ilen);
+    else {
+	StringValue(str);
+	if (RSTRING_LEN(str) >= ilen)
+	    rb_str_modify(str);
+	else
+	    rb_str_modify_expand(str, ilen - RSTRING_LEN(str));
     }
-    if(ilen == 0) return str;
+    OBJ_TAINT(str);
+    rb_str_set_len(str, 0);
+    if (ilen == 0)
+	return str;
 
     GetSSL(self, ssl);
     io = rb_attr_get(self, id_i_io);
     GetOpenFile(io, fptr);
     if (ssl_started(ssl)) {
 	for (;;){
-	    nread = SSL_read(ssl, RSTRING_PTR(str), RSTRING_LENINT(str));
+	    nread = SSL_read(ssl, RSTRING_PTR(str), ilen);
 	    switch(ssl_get_error(ssl, nread)){
 	    case SSL_ERROR_NONE:
 		goto end;
@@ -1751,8 +1757,6 @@ ossl_ssl_read_internal(int argc, VALUE *argv, VALUE self, int nonblock)
 
   end:
     rb_str_set_len(str, nread);
-    OBJ_TAINT(str);
-
     return str;
 }
 

test/test_pair.rb

@@ -239,6 +239,30 @@ def test_read_nonblock_no_exception
     }
   end
 
+  def test_read_with_outbuf
+    ssl_pair { |s1, s2|
+      s1.write("abc\n")
+      buf = ""
+      ret = s2.read(2, buf)
+      assert_same ret, buf
+      assert_equal "ab", ret
+
+      buf = "garbage"
+      ret = s2.read(2, buf)
+      assert_same ret, buf
+      assert_equal "c\n", ret
+
+      buf = "garbage"
+      assert_equal :wait_readable, s2.read_nonblock(100, buf, exception: false)
+      assert_equal "", buf
+
+      s1.close
+      buf = "garbage"
+      assert_equal nil, s2.read(100, buf)
+      assert_equal "", buf
+    }
+  end
+
   def test_write_nonblock
     ssl_pair {|s1, s2|
       assert_equal 3, s1.write_nonblock("foo")