Sharing file descriptors causes confusion; DMOJ#229

dmoj/cptbox/sandbox.py

@@ -292,7 +292,7 @@ def __init_streams(self, stdin, stdout, stderr, unbuffered):
             master, slave = pty.openpty()
 
         if stdin is PIPE:
-            self._child_stdin, self._stdin = (slave, master) if unbuffered else os.pipe()
+            self._child_stdin, self._stdin = (os.dup(slave), os.dup(master)) if unbuffered else os.pipe()
             self.stdin = os.fdopen(self._stdin, 'w')
         elif isinstance(stdin, int):
             self._child_stdin, self._stdin = stdin, -1
@@ -302,7 +302,7 @@ def __init_streams(self, stdin, stdout, stderr, unbuffered):
             self._child_stdin = self._stdin = -1
 
         if stdout is PIPE:
-            self._stdout, self._child_stdout = (master, slave) if unbuffered else os.pipe()
+            self._stdout, self._child_stdout = (os.dup(master), os.dup(slave)) if unbuffered else os.pipe()
             self.stdout = os.fdopen(self._stdout, 'r')
         elif isinstance(stdout, int):
             self._stdout, self._child_stdout = -1, stdout
@@ -321,6 +321,10 @@ def __init_streams(self, stdin, stdout, stderr, unbuffered):
         else:
             self._stderr = self._child_stderr = -1
 
+        if unbuffered:
+            os.close(master)
+            os.close(slave)
+
     # All communicate stuff copied from subprocess.
     def communicate(self, input=None):
         # Optimization: If we are only using one pipe, or no pipe at