Avoid undefined behavior in 'defvar' (Bug#31072)

* src/eval.c (Fdefvar): Check that first argument is a symbol.
* test/src/eval-tests.el (defvar/bug31072): New unit test.

2 files changed, 6 insertions, 0 deletions

diff --git a/src/eval.c b/src/eval.c
index a6e1d86c4ab..90d8c335185 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -737,6 +737,8 @@ usage: (defvar SYMBOL &optional INITVALUE DOCSTRING)  */)
   sym = XCAR (args);
   tail = XCDR (args);
 
+  CHECK_SYMBOL (sym);
+
   if (!NILP (tail))
     {
       if (!NILP (XCDR (tail)) && !NILP (XCDR (XCDR (tail))))
diff --git a/test/src/eval-tests.el b/test/src/eval-tests.el
index 59da6b7cc30..319dd91c86a 100644
--- a/test/src/eval-tests.el
+++ b/test/src/eval-tests.el
@@ -113,4 +113,8 @@ crash/abort/malloc assert failure on the next test."
         (signal-hook-function #'ignore))
     (should-error (eval-tests--exceed-specbind-limit))))
 
+(ert-deftest defvar/bug31072 ()
+  "Check that Bug#31072 is fixed."
+  (should-error (eval '(defvar 1) t) :type 'wrong-type-argument))
+
 ;;; eval-tests.el ends here