bug #470, use a dedicated lib to generate random bytes

1 files changed, 148 insertions, 0 deletions

diff --git a/include/random_compat/random_bytes_dev_urandom.php b/include/random_compat/random_bytes_dev_urandom.php
new file mode 100644
index 000000000..db93b0757
--- /dev/null
+++ b/include/random_compat/random_bytes_dev_urandom.php
@@ -0,0 +1,148 @@
+<?php
+/**
+ * Random_* Compatibility Library 
+ * for using the new PHP 7 random_* API in PHP 5 projects
+ * 
+ * The MIT License (MIT)
+ * 
+ * Copyright (c) 2015 Paragon Initiative Enterprises
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+if (!defined('RANDOM_COMPAT_READ_BUFFER')) {
+    define('RANDOM_COMPAT_READ_BUFFER', 8);
+}
+
+/**
+ * Unless open_basedir is enabled, use /dev/urandom for
+ * random numbers in accordance with best practices
+ * 
+ * Why we use /dev/urandom and not /dev/random
+ * @ref http://sockpuppet.org/blog/2014/02/25/safely-generate-random-numbers
+ * 
+ * @param int $bytes
+ * 
+ * @throws Exception
+ * 
+ * @return string
+ */
+function random_bytes($bytes)
+{
+    static $fp = null;
+    /**
+     * This block should only be run once
+     */
+    if (empty($fp)) {
+        /**
+         * We use /dev/urandom if it is a char device.
+         * We never fall back to /dev/random
+         */
+        $fp = fopen('/dev/urandom', 'rb');
+        if (!empty($fp)) {
+            $st = fstat($fp);
+            if (($st['mode'] & 0170000) !== 020000) {
+                fclose($fp);
+                $fp = false;
+            }
+        }
+
+        if (!empty($fp)) {
+            /**
+             * stream_set_read_buffer() does not exist in HHVM
+             * 
+             * If we don't set the stream's read buffer to 0, PHP will
+             * internally buffer 8192 bytes, which can waste entropy
+             * 
+             * stream_set_read_buffer returns 0 on success
+             */
+            if (function_exists('stream_set_read_buffer')) {
+                stream_set_read_buffer($fp, RANDOM_COMPAT_READ_BUFFER);
+            }
+            if (function_exists('stream_set_chunk_size')) {
+                stream_set_chunk_size($fp, RANDOM_COMPAT_READ_BUFFER);
+            }
+        }
+    }
+
+    try {
+        $bytes = RandomCompat_intval($bytes);
+    } catch (TypeError $ex) {
+        throw new TypeError(
+            'random_bytes(): $bytes must be an integer'
+        );
+    }
+
+    if ($bytes < 1) {
+        throw new Error(
+            'Length must be greater than 0'
+        );
+    }
+
+    /**
+     * This if() block only runs if we managed to open a file handle
+     * 
+     * It does not belong in an else {} block, because the above 
+     * if (empty($fp)) line is logic that should only be run once per
+     * page load.
+     */
+    if (!empty($fp)) {
+        $remaining = $bytes;
+        $buf = '';
+
+        /**
+         * We use fread() in a loop to protect against partial reads
+         */
+        do {
+            $read = fread($fp, $remaining); 
+            if ($read === false) {
+                /**
+                 * We cannot safely read from the file. Exit the
+                 * do-while loop and trigger the exception condition
+                 */
+                $buf = false;
+                break;
+            }
+            /**
+             * Decrease the number of bytes returned from remaining
+             */
+            $remaining -= RandomCompat_strlen($read);
+            $buf .= $read;
+        } while ($remaining > 0);
+        
+        /**
+         * Is our result valid?
+         */
+        if ($buf !== false) {
+            if (RandomCompat_strlen($buf) === $bytes) {
+                /**
+                 * Return our random entropy buffer here:
+                 */
+                return $buf;
+            }
+        }
+    }
+
+    /**
+     * If we reach here, PHP has failed us.
+     */
+    throw new Exception(
+        'Error reading from source device'
+    );
+}