MXS-1396: Fix persistent connection hangs

When a COM_CHANGE_USER was executed, it is possible that the server
responds with a AuthSwitchRequest packet instead of an OK packet. In this
case, the server sends a new scramble which must be used to create the 20
byte hash that is expected as the response.

include/maxscale/protocol/mysql.h

@@ -425,6 +425,9 @@ bool gw_read_backend_handshake(DCB *dcb, GWBUF *buffer);
 /** Send the server handshake response packet to the backend server */
 mxs_auth_state_t gw_send_backend_auth(DCB *dcb);
 
+/** Sends a response for an AuthSwitchRequest to the default auth plugin */
+int send_mysql_native_password_response(DCB* dcb);
+
 /** Write an OK packet to a DCB */
 int mxs_mysql_send_ok(DCB *dcb, int sequence, uint8_t affected_rows, const char* message);
 

server/modules/protocol/MySQL/MySQLBackend/mysql_backend.c

@@ -766,6 +766,43 @@ gw_read_and_write(DCB *dcb)
             MXS_INFO("Response to COM_CHANGE_USER is OK, writing stored query");
             rval = query ? dcb->func.write(dcb, query) : 1;
         }
+        else if (result == MYSQL_REPLY_AUTHSWITCHREQUEST &&
+                 gwbuf_length(reply) > MYSQL_EOF_PACKET_LEN)
+        {
+            /**
+             * The server requested a change of authentication methods.
+             * If we're changing the authentication method to the same one we
+             * are using now, it means that the server is simply generating
+             * a new scramble for the re-authentication process.
+             */
+            if (strcmp((char*)GWBUF_DATA(reply) + 5, DEFAULT_MYSQL_AUTH_PLUGIN) == 0)
+            {
+                /** Load the new scramble into the protocol... */
+                gwbuf_copy_data(reply, 5 + strlen(DEFAULT_MYSQL_AUTH_PLUGIN) + 1,
+                                GW_MYSQL_SCRAMBLE_SIZE, proto->scramble);
+
+                /** ... and use it to send the encrypted password to the server */
+                rval = send_mysql_native_password_response(dcb);
+
+                /** Store the query until we know the result of the authentication
+                 * method switch. */
+                proto->stored_query = query;
+                proto->ignore_reply = true;
+                return rval;
+            }
+            else
+            {
+                /** The server requested a change to something other than
+                 * the default auth plugin */
+                gwbuf_free(query);
+                poll_fake_hangup_event(dcb);
+
+                // TODO: Use the authenticators to handle COM_CHANGE_USER responses
+                MXS_ERROR("Received AuthSwitchRequest to '%s' when '%s' was expected",
+                          (char*)GWBUF_DATA(reply) + 5, DEFAULT_MYSQL_AUTH_PLUGIN);
+
+            }
+        }
         else
         {
             if (result == MYSQL_REPLY_ERR)
@@ -774,22 +811,13 @@ gw_read_and_write(DCB *dcb)
                  * close the DCB and send an error to the client. */
                 log_error_response(dcb, reply);
             }
-            else if (result == MYSQL_REPLY_AUTHSWITCHREQUEST &&
-                     gwbuf_length(reply) > MYSQL_EOF_PACKET_LEN)
-            {
-                MXS_ERROR("Received AuthSwitchRequest to '%s' when '%s' was expected",
-                          (char*)GWBUF_DATA(reply) + 5, DEFAULT_MYSQL_AUTH_PLUGIN);
-            }
             else
             {
                 /** This should never happen */
                 MXS_ERROR("Unknown response to COM_CHANGE_USER (0x%02hhx), "
-                          "ignoring and waiting for correct result", result);
+                          "closing connection", result);
-                gwbuf_free(reply);
-                proto->stored_query = query;
-                proto->ignore_reply = true;
-                return 1;
             }
+
             gwbuf_free(query);
             poll_fake_hangup_event(dcb);
         }

server/modules/protocol/MySQL/mysql_common.c

@@ -1205,19 +1205,19 @@ response_length(MySQLProtocol *conn, char *user, uint8_t *passwd, char *dbname,
 }
 
 /**
- * @brief Helper function to load hashed password
+ * Calculates the a hash from a scramble and a password
- * @param conn DCB Protocol object
+ *
- * @param payload Destination where hashed password is written
+ * The algorithm used is: `SHA1(scramble + SHA1(SHA1(password))) ^ SHA1(password)`
- * @param passwd Client's double SHA1 password
+ *
- * @return Address of the next byte after the end of the stored password
+ * @param scramble The 20 byte scramble sent by the server
+ * @param passwd   The SHA1(password) sent by the client
+ * @param output   Pointer where the resulting 20 byte hash is stored
  */
-static uint8_t *
+static void calculate_hash(uint8_t *scramble, uint8_t *passwd, uint8_t *output)
-load_hashed_password(uint8_t *scramble, uint8_t *payload, uint8_t *passwd)
 {
     uint8_t hash1[GW_MYSQL_SCRAMBLE_SIZE] = "";
     uint8_t hash2[GW_MYSQL_SCRAMBLE_SIZE] = "";
     uint8_t new_sha[GW_MYSQL_SCRAMBLE_SIZE] = "";
-    uint8_t client_scramble[GW_MYSQL_SCRAMBLE_SIZE];
 
     // hash1 is the function input, SHA1(real_password)
     memcpy(hash1, passwd, GW_MYSQL_SCRAMBLE_SIZE);
@@ -1229,17 +1229,24 @@ load_hashed_password(uint8_t *scramble, uint8_t *payload, uint8_t *passwd)
     gw_sha1_2_str(scramble, GW_MYSQL_SCRAMBLE_SIZE, hash2, GW_MYSQL_SCRAMBLE_SIZE, new_sha);
 
     // compute the xor in client_scramble
-    gw_str_xor(client_scramble, new_sha, hash1, GW_MYSQL_SCRAMBLE_SIZE);
+    gw_str_xor(output, new_sha, hash1, GW_MYSQL_SCRAMBLE_SIZE);
+}
 
-    // set the auth-length
+/**
-    *payload = GW_MYSQL_SCRAMBLE_SIZE;
+ * @brief Helper function to load hashed password
-    payload++;
+ *
-
+ * @param conn DCB Protocol object
-    //copy the 20 bytes scramble data after packet_buffer + 36 + user + NULL + 1 (byte of auth-length)
+ * @param payload Destination where hashed password is written
-    memcpy(payload, client_scramble, GW_MYSQL_SCRAMBLE_SIZE);
+ * @param passwd Client's double SHA1 password
-
+ *
-    payload += GW_MYSQL_SCRAMBLE_SIZE;
+ * @return Address of the next byte after the end of the stored password
-    return payload;
+ */
+static uint8_t *
+load_hashed_password(uint8_t *scramble, uint8_t *payload, uint8_t *passwd)
+{
+    *payload++ = GW_MYSQL_SCRAMBLE_SIZE;
+    calculate_hash(scramble, passwd, payload);
+    return payload + GW_MYSQL_SCRAMBLE_SIZE;
 }
 
 /**
@@ -1411,6 +1418,24 @@ mxs_auth_state_t gw_send_backend_auth(DCB *dcb)
     return dcb_write(dcb, buffer) ? MXS_AUTH_STATE_RESPONSE_SENT : MXS_AUTH_STATE_FAILED;
 }
 
+int send_mysql_native_password_response(DCB* dcb)
+{
+    MySQLProtocol* proto = (MySQLProtocol*) dcb->protocol;
+    MYSQL_session local_session;
+    gw_get_shared_session_auth_info(dcb, &local_session);
+
+    uint8_t *curr_passwd = memcmp(local_session.client_sha1, null_client_sha1, MYSQL_SCRAMBLE_LEN) ?
+        local_session.client_sha1 : null_client_sha1;
+
+    GWBUF* buffer = gwbuf_alloc(MYSQL_HEADER_LEN + GW_MYSQL_SCRAMBLE_SIZE);
+    uint8_t* data = GWBUF_DATA(buffer);
+    gw_mysql_set_byte3(data, GW_MYSQL_SCRAMBLE_SIZE);
+    data[3] = 2; // This is the third packet after the COM_CHANGE_USER
+    calculate_hash(proto->scramble, curr_passwd, data + MYSQL_HEADER_LEN);
+
+    return dcb_write(dcb, buffer);
+}
+
 /**
  * Decode mysql server handshake
  *