Add regression test

Author: SkiFire13

regex-automata/src/util/search.rs

@@ -1971,4 +1971,23 @@ mod tests {
         let expected_size = 3 * core::mem::size_of::<usize>();
         assert_eq!(expected_size, core::mem::size_of::<MatchErrorKind>());
     }
+
+    #[test]
+    fn malicious_asref_guard() {
+        struct Bad(std::cell::Cell<bool>);
+
+        impl AsRef<[u8]> for Bad {
+            fn as_ref(&self) -> &[u8] {
+                if self.0.replace(false) {
+                    &[]
+                } else {
+                    &[0; 1000]
+                }
+            }
+        }
+
+        let bad = Bad(std::cell::Cell::new(true));
+        let input = Input::new(&bad);
+        assert!(input.end() <= input.haystack().len());
+    }
 }