[gcc r11-6405] PR fortran/96381 - invalid read in gfc_find_derived_vtab

[Harald Anlauf]

https://gcc.gnu.org/g:d816b0c144d15e6570eb5b124b9f3ccbe3d40082

commit r11-6405-gd816b0c144d15e6570eb5b124b9f3ccbe3d40082
Author: Harald Anlauf <anlauf@gmx.de>
Date:   Fri Jan 1 18:55:41 2021 +0100

    PR fortran/96381 - invalid read in gfc_find_derived_vtab
    
    An invalid declaration of a CLASS instance can lead to an internal state
    with inconsistent attributes during parsing that needs to be handled with
    sufficient care when processing subsequent statements.  Avoid a lookup of
    the vtab entry for such cases.
    
    gcc/fortran/ChangeLog:
    
            * class.c (gfc_find_vtab): Add check on attribute is_class.

Diff:
---
 gcc/fortran/class.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

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.derived);
       else
 	return NULL;