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From: "anlauf at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/96381] gfc_find_vtab can use a character type typespec
 as a derived type (causing invalid access)
Date: Thu, 31 Dec 2020 21:09:43 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96381

--- Comment #2 from anlauf at gcc dot gnu.org ---
The following patch fixes the invalid read:

diff --git a/gcc/fortran/class.c b/gcc/fortran/class.c
index 5677d920239..783e4c7354b 100644
--- a/gcc/fortran/class.c
+++ b/gcc/fortran/class.c
@@ -2906,7 +2906,9 @@ gfc_find_vtab (gfc_typespec *ts)
     case BT_DERIVED:
       return gfc_find_derived_vtab (ts->u.derived);
     case BT_CLASS:
-      if (ts->u.derived->components &&
ts->u.derived->components->ts.u.derived)
+      if (ts->u.derived->attr.is_class
+         && ts->u.derived->components
+         && ts->u.derived->components->ts.u.derived)
        return gfc_find_derived_vtab (ts->u.derived->components->ts.u.deriv=
ed);
       else
        return NULL;

Not regtested yet.=