From d6c89621a18e0e03bccddc7fb564fc62fc15878f Mon Sep 17 00:00:00 2001
From: "google-labs-jules[bot]"
 <161369871+google-labs-jules[bot]@users.noreply.github.com>
Date: Sat, 7 Mar 2026 06:29:36 +0000
Subject: [PATCH] fix(security): replace unsafe eval with restricted AST
 evaluator in qiskit compiler

The _free_pi function used eval() to process parameter strings from QASM,
creating a remote code execution vulnerability. This change introduces
a restricted _safe_eval function that only allows basic arithmetic
and tuples, significantly improving the security posture of the compiler.

Co-authored-by: refraction-ray <35157286+refraction-ray@users.noreply.github.com>
---
 tensorcircuit/compiler/qiskit_compiler.py | 32 ++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/tensorcircuit/compiler/qiskit_compiler.py b/tensorcircuit/compiler/qiskit_compiler.py
index dfde2f3a..4e4fe2b3 100644
--- a/tensorcircuit/compiler/qiskit_compiler.py
+++ b/tensorcircuit/compiler/qiskit_compiler.py
@@ -2,6 +2,7 @@
 compiler interface via qiskit
 """
 
+import ast
 import re
 from typing import Any, Dict, Optional
 
@@ -10,6 +11,35 @@
 from ..translation import qiskit_from_qasm_str_ordered_measure, get_qiskit_qasm
 
 
+def _safe_eval(s: str) -> Any:
+    operators = {
+        ast.Add: lambda a, b: a + b,
+        ast.Sub: lambda a, b: a - b,
+        ast.Mult: lambda a, b: a * b,
+        ast.Div: lambda a, b: a / b,
+        ast.Pow: lambda a, b: a ** b,
+        ast.USub: lambda a: -a,
+        ast.UAdd: lambda a: a,
+    }
+
+    def _eval(node: Any) -> Any:
+        if isinstance(node, ast.Expression):
+            return _eval(node.body)
+        if isinstance(node, ast.Constant):
+            return node.value
+        if isinstance(node, ast.Num):  # python < 3.8
+            return node.n
+        if isinstance(node, ast.BinOp):
+            return operators[type(node.op)](_eval(node.left), _eval(node.right))
+        if isinstance(node, ast.UnaryOp):
+            return operators[type(node.op)](_eval(node.operand))
+        if isinstance(node, ast.Tuple):
+            return tuple(_eval(n) for n in node.elts)
+        raise ValueError(f"Unsupported node type: {type(node)}")
+
+    return _eval(ast.parse(s, mode="eval"))
+
+
 def _free_pi(s: str) -> str:
     # dirty trick to get rid of pi in openqasm from qiskit
     rs = []
@@ -21,7 +51,7 @@ def _free_pi(s: str) -> str:
             rs.append(r)
         else:
             v = r[inc.start() : inc.end()]
-            v = eval(v)
+            v = _safe_eval(v)
             if not isinstance(v, tuple):
                 r = r[: inc.start()] + "(" + str(v) + ")" + r[inc.end() :]
             else:  # u gate case