#15 - optimise file handling

main.py

@@ -69,8 +69,15 @@ class MatrixBot:
                 'next_batch': self.client.next_batch
             }
             logging.debug('save session file')
-            with open(self.session_file, 'w') as f:
-                yaml.dump(session, f)
+            # Secure file handling: set appropriate permissions (owner read/write only)
+            old_umask = os.umask(0o077)  # Restrict file permissions to owner only
+            try:
+                with open(self.session_file, 'w') as f:
+                    yaml.dump(session, f)
+                # Explicitly set file permissions to owner-only read/write (no execute)
+                os.chmod(self.session_file, 0o600)
+            finally:
+                os.umask(old_umask)  # Restore original umask
             return True
         except Exception as e:
             logging.error(f'Failed to save session to {self.session_file}: {str(e)}')
@@ -86,6 +93,12 @@ class MatrixBot:
             logging.info(f'No session file found at {self.session_file}')
             return False
         try:
+            # Security check: verify file permissions
+            file_stat = os.stat(self.session_file)
+            if file_stat.st_mode & 0o077:  # Check if other users have permissions
+                logging.warning(f'Session file {self.session_file} has insecure permissions')
+                return False
+            
             logging.info(f'restore session from file {self.session_file}')
             with open(self.session_file, 'r') as f:
                 session = yaml.safe_load(f)
@@ -96,6 +109,11 @@ class MatrixBot:
                 logging.warning('Session file exists but is incomplete')
                 return False
                 
+            # Additional integrity check: validate access token format
+            if not isinstance(session['access_token'], str) or len(session['access_token']) < 10:
+                logging.warning('Session file contains invalid access token')
+                return False
+                
             self.client.access_token    = session['access_token']
             self.client.device_id       = session['device_id']
             self.client.next_batch      = session['next_batch']