[PATCH] fix for loop assignments to nameref control vars

[Grisha Levit]

The special-case handling of namerefs as for loop control variables is
missing checks for the readonly attribute on the nameref and allows
creation of forbidden nameref self-references.

$ declare -rn ref=a
$ for ref in b; { :; }
$ declare -p ref
declare -nr ref="b"

$ declare -n ref
$ for ref in ref; { declare -p ref; }
declare -n ref="ref"


---
 execute_cmd.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/execute_cmd.c b/execute_cmd.c
index feccf7c7..71bbfb4e 100644
--- a/execute_cmd.c
+++ b/execute_cmd.c
@@ -2800,8 +2800,10 @@ execute_for_command (for_command)
              sh_invalidid (list->word->word);
              v = 0;
            }
+         else if (readonly_p (v))
+           err_readonly (name_cell (v));
          else
-           v = bind_variable_value (v, list->word->word, 0);
+           v = bind_variable_value (v, list->word->word, ASS_NAMEREF);
        }
       else
        v = bind_variable (identifier, list->word->word, 0);
--