dynamic clients configuration may cause radiusd 3.2.0 (and earlier) to hang

[Sam Yee]

Hi freeradius devs.  I was able to cause radiusd to hang by configuring a dynamic client in SQL using the same shared secret of an existing static client.  It causes a loop in a linked list.  Here is the fix:

--- cut ---
--- freeradius-server-3.2.0/src/main/client.c.orig      2022-04-21 13:11:17.000000000 -0700
+++ freeradius-server-3.2.0/src/main/client.c   2022-07-12 16:05:13.900988256 -0700
@@ -1425,7 +1425,13 @@
                } else {
                        RDEBUG2("%s = %s", cf_pair_attr(cp), cf_pair_value(cp));
                }
-               cf_pair_add(c->cs, cp);
+
+               if (cp != NULL)
+               {
+                       cf_pair_add(c->cs, cp);
+               }
+
+               cp = NULL;

                talloc_free(vp);
        }
--- cut ---

After calling cf_pair_add(), cp is added to the list.  In the next loop iteration, cp may not be re-allocated, and it is attempted to be re-added to the list.  cp's next pointer points back to itself.  Please let me know if the fix can make it to the next stable release.

Thanks,
Sam