Date:   Tue, 21 Mar 2023 13:58:54 +0000
From:   Chuck Lever III <chuck.lever@...cle.com>
To:     Paolo Abeni <pabeni@...hat.com>
CC:     Chuck Lever <cel@...nel.org>, Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        "open list:NETWORKING [GENERAL]" <netdev@...r.kernel.org>,
        "kernel-tls-handshake@...ts.linux.dev" 
        <kernel-tls-handshake@...ts.linux.dev>,
        John Haxby <john.haxby@...cle.com>
Subject: Re: [PATCH v7 1/2] net/handshake: Create a NETLINK service for
 handling handshake requests



> On Mar 21, 2023, at 7:27 AM, Paolo Abeni <pabeni@...hat.com> wrote:
> 
> 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.

If we rely on sk_destruct to release the final reference count,
it will never get invoked.


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

I will do that.

Personally, I find it more clear to bump a reference count when
saving a copy of the object's pointer, as is done in _alloc. But if
others find it easier the other way, I have no problem changing
it to suit community preferences.


>> +
>> +	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 ;)

Interesting. I like reverse-xmas, but I thought that the initialization
of these variables would take precedent. I'll clean this up.


>> +
>> +	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.

I'll move the sock_hold() to _submit, and cook up a comment or two.


> 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?

I'm comfortable with Kunit, having just added a bunch of tests
for the kernel's SunRPC GSS Kerberos implementation.

There, however, I had clearly defined test cases to add, thanks
to the RFCs. I guess I'm a little unclear on what specific tests
would be necessary or valuable here. Suggestions and existing
examples are very welcome.


--
Chuck Lever

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