bug#24118: 25.1; [PATCH] Fix a possible crash caused by mapcar1

[Chris Feng]

Processing a list with `mapcar' or `mapconcat' can be terminated early
when the list is tampered (as shown in the following example), and as a
result we'll be dealing with uninitialized memory which will likely
trigger a crash.

  (setq a (make-list 10 0))
  (mapcar (lambda (_)
            (setcdr a nil))
          a)

Chris

---

* src/fns.c (mapcar1): Check and reset uninitialized list elements.
---
 src/fns.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/fns.c b/src/fns.c
index d5a1f74..1804bce 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -2524,6 +2524,10 @@ mapcar1 (EMACS_INT leni, Lisp_Object *vals, Lisp_Object 
fn, Lisp_Object seq)
            vals[i] = dummy;
          tail = XCDR (tail);
        }
+
+      /* In case the list was tampered and the loop terminated early. */
+      if (i < leni)
+        memclear (vals + i, (leni - i) * word_size);
     }
 }
 
-- 
2.8.1