SSH2: add support for zlib and zlib@openssh.com compression

phpseclib/Net/SSH2.php

@@ -150,6 +150,23 @@ define('NET_SSH2_READ_REGEX', 2);
 define('NET_SSH2_READ_NEXT', 3);
 /**#@-*/
 
+/**#@+
+ * @access private
+ */
+/**
+ * No compression
+ */
+define('NET_SSH2_COMPRESSION_NONE',  1);
+/**
+ * zlib compression
+ */
+define('NET_SSH2_COMPRESSION_ZLIB', 2);
+/**
+ * zlib@openssh.com
+ */
+define('NET_SSH2_COMPRESSION_ZLIB_AT_OPENSSH', 3);
+/**#@-*/
+
 /**
  * Pure-PHP implementation of SSHv2.
  *
@@ -980,8 +997,57 @@ class Net_SSH2
      *
      * @see https://tools.ietf.org/html/rfc4252#section-5.1
      * @var array|null
+     * @access private
      */
-    private $auth_methods_to_continue = null;
+    var $auth_methods_to_continue = null;
+
+    /**
+     * Compression method
+     *
+     * @var int
+     * @access private
+     */
+    var $compress = NET_SSH2_COMPRESSION_NONE;
+
+    /**
+     * Decompression method
+     *
+     * @var resource|object
+     * @access private
+     */
+    var $decompress = NET_SSH2_COMPRESSION_NONE;
+
+    /**
+     * Compression context
+     *
+     * @var int
+     * @access private
+     */
+    var $compress_context;
+
+    /**
+     * Decompression context
+     *
+     * @var resource|object
+     * @access private
+     */
+    var $decompress_context;
+
+    /**
+     * Regenerate Compression Context
+     *
+     * @var bool
+     * @access private
+     */
+    var $regenerate_compression_context = false;
+
+    /**
+     * Regenerate Decompression Context
+     *
+     * @var bool
+     * @access private
+     */
+    var $regenerate_decompression_context = false;
 
     /**
      * Default Constructor.
@@ -1590,19 +1656,25 @@ class Net_SSH2
             return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
         }
 
+        $compression_map = array(
+            'none' => NET_SSH2_COMPRESSION_NONE,
+            'zlib' => NET_SSH2_COMPRESSION_ZLIB,
+            'zlib@openssh.com' => NET_SSH2_COMPRESSION_ZLIB_AT_OPENSSH
+        );
+
         $compression_algorithm_out = $this->_array_intersect_first($c2s_compression_algorithms, $this->compression_algorithms_client_to_server);
         if ($compression_algorithm_out === false) {
             user_error('No compatible client to server compression algorithms found');
             return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
         }
-        //$this->decompress = $compression_algorithm_out == 'zlib';
+        $this->compress = $compression_map[$compression_algorithm_out];
 
-        $compression_algorithm_in = $this->_array_intersect_first($s2c_compression_algorithms, $this->compression_algorithms_client_to_server);
+        $compression_algorithm_in = $this->_array_intersect_first($s2c_compression_algorithms, $this->compression_algorithms_server_to_client);
         if ($compression_algorithm_in === false) {
             user_error('No compatible server to client compression algorithms found');
             return $this->_disconnect(NET_SSH2_DISCONNECT_KEY_EXCHANGE_FAILED);
         }
-        //$this->compress = $compression_algorithm_in == 'zlib';
+        $this->decompress = $compression_map[$compression_algorithm_in];
 
         if (strpos($kex_algorithm, 'diffie-hellman-group-exchange') === 0) {
             $dh_group_sizes_packed = pack(
@@ -1996,6 +2068,8 @@ class Net_SSH2
         }
         $this->hmac_check->setKey(substr($key, 0, $checkKeyLength));
 
+        $this->regenerate_compression_context = $this->regenerate_decompression_context = true;
+
         return true;
     }
 
@@ -3399,7 +3473,7 @@ class Net_SSH2
 
         if (!is_resource($this->fsock) || feof($this->fsock)) {
             $this->bitmap = 0;
-            user_error('Connection closed (by server) prematurely');
+            user_error('Connection closed (by server) prematurely ' . $elapsed . 's');
             return false;
         }
 
@@ -3470,9 +3544,41 @@ class Net_SSH2
             }
         }
 
-        //if ($this->decompress) {
+        switch ($this->decompress) {
-        //    $payload = gzinflate(substr($payload, 2));
+            case NET_SSH2_COMPRESSION_ZLIB_AT_OPENSSH:
-        //}
+                if (!$this->isAuthenticated()) {
+                    break;
+                }
+            case NET_SSH2_COMPRESSION_ZLIB:
+                if ($this->regenerate_decompression_context) {
+                    $this->regenerate_decompression_context = false;
+
+                    $cmf = ord($payload[0]);
+                    $cm = $cmf & 0x0F;
+                    if ($cm != 8) { // deflate
+                        user_error("Only CM = 8 ('deflate') is supported ($cm)");
+                    }
+                    $cinfo = ($cmf & 0xF0) >> 4;
+                    if ($cinfo > 7) {
+                        user_error("CINFO above 7 is not allowed ($cinfo)");
+                    }
+                    $windowSize = 1 << ($cinfo + 8);
+
+                    $flg = ord($payload[1]);
+                    //$fcheck = $flg && 0x0F;
+                    if ((($cmf << 8) | $flg) % 31) {
+                        user_error('fcheck failed');
+                    }
+                    $fdict = boolval($flg & 0x20);
+                    $flevel = ($flg & 0xC0) >> 6;
+
+                    $this->decompress_context = inflate_init(ZLIB_ENCODING_RAW, ['window' => $cinfo + 8]);
+                    $payload = substr($payload, 2);
+                }
+                if ($this->decompress_context) {
+                    $payload = inflate_add($this->decompress_context, $payload, ZLIB_PARTIAL_FLUSH);
+                }
+        }
 
         $this->get_seq_no++;
 
@@ -4028,11 +4134,27 @@ class Net_SSH2
             return false;
         }
 
-        //if ($this->compress) {
+        if (!isset($logged)) {
-        //    // the -4 removes the checksum:
+            $logged = $data;
-        //    // http://php.net/function.gzcompress#57710
+        }
-        //    $data = substr(gzcompress($data), 0, -4);
+
-        //}
+        switch ($this->compress) {
+            case NET_SSH2_COMPRESSION_ZLIB_AT_OPENSSH:
+                if (!$this->isAuthenticated()) {
+                    break;
+                }
+            case NET_SSH2_COMPRESSION_ZLIB:
+                if (!$this->regenerate_compression_context) {
+                    $header = '';
+                } else {
+                    $this->regenerate_compression_context = false;
+                    $this->compress_context = deflate_init(ZLIB_ENCODING_RAW, ['window' => 15]);
+                    $header = "\x78\x9C";
+                }
+                if ($this->compress_context) {
+                    $data = $header . deflate_add($this->compress_context, $data, ZLIB_PARTIAL_FLUSH);
+                }
+        }
 
         // 4 (packet length) + 1 (padding length) + 4 (minimal padding amount) == 9
         $packet_length = strlen($data) + 9;
@@ -4060,10 +4182,10 @@ class Net_SSH2
 
         if (defined('NET_SSH2_LOGGING')) {
             $current = strtok(microtime(), ' ') + strtok('');
-            $message_number = isset($this->message_numbers[ord($data[0])]) ? $this->message_numbers[ord($data[0])] : 'UNKNOWN (' . ord($data[0]) . ')';
+            $message_number = isset($this->message_numbers[ord($logged[0])]) ? $this->message_numbers[ord($logged[0])] : 'UNKNOWN (' . ord($logged[0]) . ')';
             $message_number = '-> ' . $message_number .
                               ' (since last: ' . round($current - $this->last_packet, 4) . ', network: ' . round($stop - $start, 4) . 's)';
-            $this->_append_log($message_number, isset($logged) ? $logged : $data);
+            $this->_append_log($message_number, $logged);
             $this->last_packet = $current;
         }
 
@@ -4746,10 +4868,12 @@ class Net_SSH2
      */
     function getSupportedCompressionAlgorithms()
     {
-        return array(
+        $algos = array('none'); // REQUIRED        no compression
-            'none'   // REQUIRED        no compression
+        if (function_exists('deflate_init')) {
-            //'zlib' // OPTIONAL        ZLIB (LZ77) compression
+            $algos[] = 'zlib@openssh.com'; // https://datatracker.ietf.org/doc/html/draft-miller-secsh-compression-delayed
-        );
+            $algos[] = 'zlib';
+        }
+        return $algos;
     }
 
     /**
@@ -4764,18 +4888,24 @@ class Net_SSH2
     {
         $this->_connect();
 
+        $compression_map = array(
+            NET_SSH2_COMPRESSION_NONE => 'none',
+            NET_SSH2_COMPRESSION_ZLIB => 'zlib',
+            NET_SSH2_COMPRESSION_ZLIB_AT_OPENSSH => 'zlib@openssh.com'
+        );
+
         return array(
             'kex' => $this->kex_algorithm,
             'hostkey' => $this->signature_format,
             'client_to_server' => array(
                 'crypt' => $this->encrypt->name,
                 'mac' => $this->hmac_create->name,
-                'comp' => 'none',
+                'comp' => $compression_map[$this->compress],
             ),
             'server_to_client' => array(
                 'crypt' => $this->decrypt->name,
                 'mac' => $this->hmac_check->name,
-                'comp' => 'none',
+                'comp' => $compression_map[$this->decompress],
             )
         );
     }