Raise an exception when transfer arguments are too many; fix #3641

The fix was proposed by @block8437.  Thank you.

1 files changed, 6 insertions, 2 deletions

diff --git a/mrbgems/mruby-fiber/src/fiber.c b/mrbgems/mruby-fiber/src/fiber.c
index bd1d09d43..bc1d82bbc 100644
--- a/mrbgems/mruby-fiber/src/fiber.c
+++ b/mrbgems/mruby-fiber/src/fiber.c
@@ -188,9 +188,13 @@ fiber_switch(mrb_state *mrb, mrb_value self, mrb_int len, const mrb_value *a, mr
   mrb->c->status = resume ? MRB_FIBER_RESUMED : MRB_FIBER_TRANSFERRED;
   c->prev = resume ? mrb->c : (c->prev ? c->prev : mrb->root_c);
   if (c->status == MRB_FIBER_CREATED) {
-    mrb_value *b = c->stack+1;
-    mrb_value *e = b + len;
+    mrb_value *b, *e;
 
+    if (len > c->stend - c->stack) {
+      mrb_raise(mrb, E_FIBER_ERROR, "too many arguments to fiber");
+    }
+    b = c->stack+1;
+    e = b + len;
     while (b<e) {
       *b++ = *a++;
     }