Re: [PATCH v7 1/2] net/handshake: Create a NETLINK service for handling handshake requests

[Paolo Abeni <pabeni@redhat.com>]

On Sat, 2023-03-18 at 12:18 -0400, Chuck Lever wrote:
> +/**
> + * handshake_req_alloc - consumer API to allocate a request
> + * @sock: open socket on which to perform a handshake
> + * @proto: security protocol
> + * @flags: memory allocation flags
> + *
> + * Returns an initialized handshake_req or NULL.
> + */
> +struct handshake_req *handshake_req_alloc(struct socket *sock,
> +					  const struct handshake_proto *proto,
> +					  gfp_t flags)
> +{
> +	struct sock *sk = sock->sk;
> +	struct net *net = sock_net(sk);
> +	struct handshake_net *hn = handshake_pernet(net);
> +	struct handshake_req *req;
> +
> +	if (!hn)
> +		return NULL;
> +
> +	req = kzalloc(struct_size(req, hr_priv, proto->hp_privsize), flags);
> +	if (!req)
> +		return NULL;
> +
> +	sock_hold(sk);

The hr_sk reference counting is unclear to me. It looks like
handshake_req retain a reference to such socket, but
handshake_req_destroy()/handshake_sk_destruct() do not release it.

Perhaps is better moving such sock_hold() into handshake_req_submit(),
once that the request is successful?

> +
> +	INIT_LIST_HEAD(&req->hr_list);
> +	req->hr_sk = sk;
> +	req->hr_proto = proto;
> +	return req;
> +}
> +EXPORT_SYMBOL(handshake_req_alloc);
> +
> +/**
> + * handshake_req_private - consumer API to return per-handshake private data
> + * @req: handshake arguments
> + *
> + */
> +void *handshake_req_private(struct handshake_req *req)
> +{
> +	return (void *)&req->hr_priv;
> +}
> +EXPORT_SYMBOL(handshake_req_private);
> +
> +static bool __add_pending_locked(struct handshake_net *hn,
> +				 struct handshake_req *req)
> +{
> +	if (!list_empty(&req->hr_list))
> +		return false;
> +	hn->hn_pending++;
> +	list_add_tail(&req->hr_list, &hn->hn_requests);
> +	return true;
> +}
> +
> +void __remove_pending_locked(struct handshake_net *hn,
> +			     struct handshake_req *req)
> +{
> +	hn->hn_pending--;
> +	list_del_init(&req->hr_list);
> +}
> +
> +/*
> + * Returns %true if the request was found on @net's pending list,
> + * otherwise %false.
> + *
> + * If @req was on a pending list, it has not yet been accepted.
> + */
> +static bool remove_pending(struct handshake_net *hn, struct handshake_req *req)
> +{
> +	bool ret;
> +
> +	ret = false;

Nit: merge the initialization and the declaration

> +
> +	spin_lock(&hn->hn_lock);
> +	if (!list_empty(&req->hr_list)) {
> +		__remove_pending_locked(hn, req);
> +		ret = true;
> +	}
> +	spin_unlock(&hn->hn_lock);
> +
> +	return ret;
> +}
> +
> +/**
> + * handshake_req_submit - consumer API to submit a handshake request
> + * @req: handshake arguments
> + * @flags: memory allocation flags
> + *
> + * Return values:
> + *   %0: Request queued
> + *   %-EBUSY: A handshake is already under way for this socket
> + *   %-ESRCH: No handshake agent is available
> + *   %-EAGAIN: Too many pending handshake requests
> + *   %-ENOMEM: Failed to allocate memory
> + *   %-EMSGSIZE: Failed to construct notification message
> + *   %-EOPNOTSUPP: Handshake module not initialized
> + *
> + * A zero return value from handshake_request() means that
> + * exactly one subsequent completion callback is guaranteed.
> + *
> + * A negative return value from handshake_request() means that
> + * no completion callback will be done and that @req has been
> + * destroyed.
> + */
> +int handshake_req_submit(struct handshake_req *req, gfp_t flags)
> +{
> +	struct sock *sk = req->hr_sk;
> +	struct net *net = sock_net(sk);
> +	struct handshake_net *hn = handshake_pernet(net);
> +	int ret;

Nit: reverse xmas tree. In this case you have to split declaration and
initialization ;)

> +
> +	if (!hn)
> +		return -EOPNOTSUPP;
> +
> +	ret = -EAGAIN;
> +	if (READ_ONCE(hn->hn_pending) >= hn->hn_pending_max)
> +		goto out_err;
> +
> +	req->hr_odestruct = sk->sk_destruct;
> +	sk->sk_destruct = handshake_sk_destruct;
> +	spin_lock(&hn->hn_lock);
> +	ret = -EOPNOTSUPP;
> +	if (test_bit(HANDSHAKE_F_NET_DRAINING, &hn->hn_flags))
> +		goto out_unlock;
> +	ret = -EBUSY;
> +	if (!handshake_req_hash_add(req))
> +		goto out_unlock;
> +	if (!__add_pending_locked(hn, req))
> +		goto out_unlock;
> +	spin_unlock(&hn->hn_lock);
> +
> +	ret = handshake_genl_notify(net, req->hr_proto->hp_handler_class,
> +				    flags);
> +	if (ret) {
> +		trace_handshake_notify_err(net, req, sk, ret);
> +		if (remove_pending(hn, req))
> +			goto out_err;
> +	}
> +
> +	trace_handshake_submit(net, req, sk);
> +	return 0;
> +
> +out_unlock:
> +	spin_unlock(&hn->hn_lock);
> +out_err:
> +	trace_handshake_submit_err(net, req, sk, ret);
> +	handshake_req_destroy(req);
> +	return ret;
> +}
> +EXPORT_SYMBOL(handshake_req_submit);
> +
> +void handshake_complete(struct handshake_req *req, unsigned int status,
> +			struct genl_info *info)
> +{
> +	struct sock *sk = req->hr_sk;
> +	struct net *net = sock_net(sk);
> +
> +	if (!test_and_set_bit(HANDSHAKE_F_REQ_COMPLETED, &req->hr_flags)) {
> +		trace_handshake_complete(net, req, sk, status);
> +		req->hr_proto->hp_done(req, status, info);
> +		__sock_put(sk);

Is unclear to me who acquired the reference released above?!? If that
is the reference acquire by handshake_req_alloc(), I think it's cleaner
moving the sock_put() in handshake_req_destroy() or
handshake_req_destroy()

> +	}
> +}
> +
> +/**
> + * handshake_req_cancel - consumer API to cancel an in-progress handshake
> + * @sock: socket on which there is an ongoing handshake
> + *
> + * XXX: Perhaps killing the user space agent might also be necessary?
> + *
> + * Request cancellation races with request completion. To determine
> + * who won, callers examine the return value from this function.
> + *
> + * Return values:
> + *   %true - Uncompleted handshake request was canceled or not found
> + *   %false - Handshake request already completed
> + */
> +bool handshake_req_cancel(struct socket *sock)
> +{
> +	struct handshake_req *req;
> +	struct handshake_net *hn;
> +	struct sock *sk;
> +	struct net *net;
> +
> +	sk = sock->sk;
> +	net = sock_net(sk);
> +	req = handshake_req_hash_lookup(sk);
> +	if (!req) {
> +		trace_handshake_cancel_none(net, req, sk);
> +		return true;
> +	}
> +
> +	hn = handshake_pernet(net);
> +	if (hn && remove_pending(hn, req)) {
> +		/* Request hadn't been accepted */
> +		trace_handshake_cancel(net, req, sk);
> +		return true;
> +	}
> +	if (test_and_set_bit(HANDSHAKE_F_REQ_COMPLETED, &req->hr_flags)) {
> +		/* Request already completed */
> +		trace_handshake_cancel_busy(net, req, sk);
> +		return false;
> +	}
> +
> +	__sock_put(sk);

Same here.

Side note, I think at this point some tests could surface here? If
user-space-based self-tests are too cumbersome and/or do not offer
adequate coverage perhaps you could consider using kunit?

Cheers,

Paolo