[njs] Fixed RegExp.prototype.exec() when second argument is absent.

[Dmitry Volyntsev]

details:   https://hg.nginx.org/njs/rev/275d785ab5bf
branches:  
changeset: 2257:275d785ab5bf
user:      Dmitry Volyntsev <xeioex at nginx.com>
date:      Mon Jan 08 16:40:42 2024 -0800
description:
Fixed RegExp.prototype.exec() when second argument is absent.

Previously, when the second argument is undefined, NaN is casted to
unsigned which is undefined behavior.

Found by UndefinedBehaviorSanitizer.

diffstat:

 src/njs_regexp.c |  11 +++++++++--
 1 files changed, 9 insertions(+), 2 deletions(-)

diffs (28 lines):

diff -r 41d0de3ad198 -r 275d785ab5bf src/njs_regexp.c
--- a/src/njs_regexp.c	Mon Jan 08 16:40:42 2024 -0800
+++ b/src/njs_regexp.c	Mon Jan 08 16:40:42 2024 -0800
@@ -1235,6 +1235,7 @@ njs_int_t
 njs_regexp_prototype_exec(njs_vm_t *vm, njs_value_t *args, njs_uint_t nargs,
     njs_index_t unused, njs_value_t *retval)
 {
+    unsigned     flags;
     njs_int_t    ret;
     njs_value_t  *r, *s;
     njs_value_t  string_lvalue;
@@ -1253,8 +1254,14 @@ njs_regexp_prototype_exec(njs_vm_t *vm, 
         return ret;
     }
 
-    return njs_regexp_builtin_exec(vm, r, s,
-                                   njs_number(njs_arg(args, nargs, 2)), retval);
+    if (nargs > 2) {
+        flags = njs_number(njs_arg(args, nargs, 2));
+
+    } else {
+        flags = 0;
+    }
+
+    return njs_regexp_builtin_exec(vm, r, s, flags, retval);
 }