Subject: Re: [PATCH net-next 1/3] net: qrtr: ns: Change servers radix tree to xarray

From: Simon Horman <[email-masked]>
Date: Thu, 13 Jul 2023 15:54:01 +0100

On Wed, Jul 12, 2023 at 04:56:29PM +0530, Vignesh Viswanathan wrote:
> There is a use after free scenario while iterating through the servers
> radix tree despite the ns being a single threaded process. This can
> happen when the radix tree APIs are not synchronized with the
> rcu_read_lock() APIs.
> 
> Convert the radix tree for servers to xarray to take advantage of the
> built in rcu lock usage provided by xarray.
> 
> Signed-off-by: Chris Lew <[email-masked]>
> Signed-off-by: Vignesh Viswanathan <[email-masked]>

Reviewed-by: Simon Horman <[email-masked]>

A few very minor nits below.

...

> @@ -256,14 +240,17 @@ static struct qrtr_server *server_add(unsigned int service,
>  		goto err;
>  
>  	/* Delete the old server on the same port */
> -	old = radix_tree_lookup(&node->servers, port);
> +	old = xa_store(&node->servers, port, srv, GFP_KERNEL);
>  	if (old) {
> -		radix_tree_delete(&node->servers, port);
> -		kfree(old);
> +		if (xa_is_err(old)) {
> +			pr_err("failed to add server [0x%x:0x%x] ret:%d\n",
> +				srv->service, srv->instance, xa_err(old));

The indentation of the line above is not correct.
It should be:

			pr_err("failed to add server [0x%x:0x%x] ret:%d\n",
			       srv->service, srv->instance, xa_err(old));

> +			goto err;
> +		} else {
> +			kfree(old);
> +		}
>  	}
>  
> -	radix_tree_insert(&node->servers, port, srv);
> -
>  	trace_qrtr_ns_server_add(srv->service, srv->instance,
>  				 srv->node, srv->port);
>  

...

> @@ -576,13 +518,12 @@ static int ctrl_cmd_del_server(struct sockaddr_qrtr *from,
>  static int ctrl_cmd_new_lookup(struct sockaddr_qrtr *from,
>  			       unsigned int service, unsigned int instance)
>  {
> -	struct radix_tree_iter node_iter;
>  	struct qrtr_server_filter filter;
> -	struct radix_tree_iter srv_iter;
>  	struct qrtr_lookup *lookup;
>  	struct qrtr_node *node;
> -	void __rcu **node_slot;
> -	void __rcu **srv_slot;
> +	struct qrtr_server *srv;

This breaks reverse xmas tree ordering of local variables.
The srv line should be directly above rather than below the node line.

> +	unsigned long node_idx;
> +	unsigned long srv_idx;
>  
>  	/* Accept only local observers */
>  	if (from->sq_node != qrtr_ns.local_node)

...