For child libctx / provider, don't count self-references in parent

In child library contexts, which contain child "clones" of the
providers the application has in store, one of these children will
always be the provider that creates the child library context; let's
call them self-refering child providers.

For these self-refering child providers, we don't increment the parent
provider reference count, nor do we free the parent provider, as those
become self defeating and hinder the teardown and unloading process
when the application cleans up.

For non self-refering child providers, we must retain this propagation
of reference count to the parent, so that aren't torn down too early,
i.e. when there's still a "foreign" reference (fetched algorithm).

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/18151)

crypto/provider_child.c

@@ -269,26 +269,46 @@ void ossl_provider_deinit_child(OSSL_LIB_CTX *ctx)
     gbl->c_provider_deregister_child_cb(gbl->handle);
 }
 
+/*
+ * ossl_provider_up_ref_parent() and ossl_provider_free_parent() do
+ * nothing in "self-referencing" child providers, i.e. when the parent
+ * of the child provider is the same as the provider where this child
+ * provider was created.
+ * This allows the teardown function in the parent provider to be called
+ * at the correct moment.
+ * For child providers in other providers, the reference count is done to
+ * ensure that cross referencing is recorded.  These should be cleared up
+ * through that providers teardown, as part of freeing its child libctx.
+ */
+
 int ossl_provider_up_ref_parent(OSSL_PROVIDER *prov, int activate)
 {
     struct child_prov_globals *gbl;
+    const OSSL_CORE_HANDLE *parent_handle;
 
     gbl = ossl_lib_ctx_get_data(ossl_provider_libctx(prov),
                                 OSSL_LIB_CTX_CHILD_PROVIDER_INDEX);
     if (gbl == NULL)
         return 0;
 
-    return gbl->c_prov_up_ref(ossl_provider_get_parent(prov), activate);
+    parent_handle = ossl_provider_get_parent(prov);
+    if (parent_handle == gbl->handle)
+        return 1;
+    return gbl->c_prov_up_ref(parent_handle, activate);
 }
 
 int ossl_provider_free_parent(OSSL_PROVIDER *prov, int deactivate)
 {
     struct child_prov_globals *gbl;
+    const OSSL_CORE_HANDLE *parent_handle;
 
     gbl = ossl_lib_ctx_get_data(ossl_provider_libctx(prov),
                                 OSSL_LIB_CTX_CHILD_PROVIDER_INDEX);
     if (gbl == NULL)
         return 0;
 
+    parent_handle = ossl_provider_get_parent(prov);
+    if (parent_handle == gbl->handle)
+        return 1;
     return gbl->c_prov_free(ossl_provider_get_parent(prov), deactivate);
 }