x509: Fix possible use-after-free when OOM

ossl_policy_level_add_node() first adds the new node to the level->nodes
stack, and then attempts to add extra data if extra_data is true. If
memory allocation or adding the extra data to tree->extra_data fails,
the allocated node (that has already been added to the level->nodes
stack) is freed using ossl_policy_node_free(), which leads to
a potential use after free.

Additionally, the tree's node count and the parent's child count would
not be updated, despite the new node being added.

Fix this by either performing the function's purpose completely, or not
at all by reverting the changes on error.

Signed-off-by: Clemens Lang <cllang@redhat.com>

Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Bernd Edlinger <bernd.edlinger@hotmail.de>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from #21066)

crypto/x509v3/pcy_node.c

@@ -100,11 +100,11 @@ X509_POLICY_NODE *level_add_node(X509_POLICY_LEVEL *level,
             tree->extra_data = sk_X509_POLICY_DATA_new_null();
         if (tree->extra_data == NULL){
             X509V3err(X509V3_F_LEVEL_ADD_NODE, ERR_R_MALLOC_FAILURE);
-            goto node_error;
+            goto extra_data_error;
         }
         if (!sk_X509_POLICY_DATA_push(tree->extra_data, data)) {
             X509V3err(X509V3_F_LEVEL_ADD_NODE, ERR_R_MALLOC_FAILURE);
-            goto node_error;
+            goto extra_data_error;
         }
     }
 
@@ -114,6 +114,14 @@ X509_POLICY_NODE *level_add_node(X509_POLICY_LEVEL *level,
 
     return node;
 
+ extra_data_error:
+    if (level != NULL) {
+        if (level->anyPolicy == node)
+            level->anyPolicy = NULL;
+        else
+            (void) sk_X509_POLICY_NODE_pop(level->nodes);
+    }
+
  node_error:
     policy_node_free(node);
     return NULL;