net/handshake: Create a NETLINK service for handling handshake requests

When a kernel consumer needs a transport layer security session, it
first needs a handshake to negotiate and establish a session. This
negotiation can be done in user space via one of the several
existing library implementations, or it can be done in the kernel.

No in-kernel handshake implementations yet exist. In their absence,
we add a netlink service that can:

a. Notify a user space daemon that a handshake is needed.

b. Once notified, the daemon calls the kernel back via this
   netlink service to get the handshake parameters, including an
   open socket on which to establish the session.

c. Once the handshake is complete, the daemon reports the
   session status and other information via a second netlink
   operation. This operation marks that it is safe for the
   kernel to use the open socket and the security session
   established there.

The notification service uses a multicast group. Each handshake
mechanism (eg, tlshd) adopts its own group number so that the
handshake services are completely independent of one another. The
kernel can then tell via netlink_has_listeners() whether a handshake
service is active and prepared to handle a handshake request.

A new netlink operation, ACCEPT, acts like accept(2) in that it
instantiates a file descriptor in the user space daemon's fd table.
If this operation is successful, the reply carries the fd number,
which can be treated as an open and ready file descriptor.

While user space is performing the handshake, the kernel keeps its
muddy paws off the open socket. A second new netlink operation,
DONE, indicates that the user space daemon is finished with the
socket and it is safe for the kernel to use again. The operation
also indicates whether a session was established successfully.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 339 insertions, 0 deletions

diff --git a/net/handshake/request.c b/net/handshake/request.c
new file mode 100644
index 000000000000..d5b2bc6de057
--- /dev/null
+++ b/net/handshake/request.c
@@ -0,0 +1,339 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Handshake request lifetime events
+ *
+ * Author: Chuck Lever <chuck.lever@oracle.com>
+ *
+ * Copyright (c) 2023, Oracle and/or its affiliates.
+ */
+
+#include <linux/types.h>
+#include <linux/socket.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/inet.h>
+#include <linux/fdtable.h>
+#include <linux/rhashtable.h>
+
+#include <net/sock.h>
+#include <net/genetlink.h>
+#include <net/netns/generic.h>
+
+#include <uapi/linux/handshake.h>
+#include "handshake.h"
+
+#include <trace/events/handshake.h>
+
+/*
+ * We need both a handshake_req -> sock mapping, and a sock ->
+ * handshake_req mapping. Both are one-to-one.
+ *
+ * To avoid adding another pointer field to struct sock, net/handshake
+ * maintains a hash table, indexed by the memory address of @sock, to
+ * find the struct handshake_req outstanding for that socket. The
+ * reverse direction uses a simple pointer field in the handshake_req
+ * struct.
+ */
+
+static struct rhashtable handshake_rhashtbl ____cacheline_aligned_in_smp;
+
+static const struct rhashtable_params handshake_rhash_params = {
+	.key_len		= sizeof_field(struct handshake_req, hr_sk),
+	.key_offset		= offsetof(struct handshake_req, hr_sk),
+	.head_offset		= offsetof(struct handshake_req, hr_rhash),
+	.automatic_shrinking	= true,
+};
+
+int handshake_req_hash_init(void)
+{
+	return rhashtable_init(&handshake_rhashtbl, &handshake_rhash_params);
+}
+
+void handshake_req_hash_destroy(void)
+{
+	rhashtable_destroy(&handshake_rhashtbl);
+}
+
+struct handshake_req *handshake_req_hash_lookup(struct sock *sk)
+{
+	return rhashtable_lookup_fast(&handshake_rhashtbl, &sk,
+				      handshake_rhash_params);
+}
+
+static bool handshake_req_hash_add(struct handshake_req *req)
+{
+	int ret;
+
+	ret = rhashtable_lookup_insert_fast(&handshake_rhashtbl,
+					    &req->hr_rhash,
+					    handshake_rhash_params);
+	return ret == 0;
+}
+
+static void handshake_req_destroy(struct handshake_req *req)
+{
+	if (req->hr_proto->hp_destroy)
+		req->hr_proto->hp_destroy(req);
+	rhashtable_remove_fast(&handshake_rhashtbl, &req->hr_rhash,
+			       handshake_rhash_params);
+	kfree(req);
+}
+
+static void handshake_sk_destruct(struct sock *sk)
+{
+	void (*sk_destruct)(struct sock *sk);
+	struct handshake_req *req;
+
+	req = handshake_req_hash_lookup(sk);
+	if (!req)
+		return;
+
+	trace_handshake_destruct(sock_net(sk), req, sk);
+	sk_destruct = req->hr_odestruct;
+	handshake_req_destroy(req);
+	if (sk_destruct)
+		sk_destruct(sk);
+}
+
+/**
+ * handshake_req_alloc - Allocate a handshake request
+ * @proto: security protocol
+ * @flags: memory allocation flags
+ *
+ * Returns an initialized handshake_req or NULL.
+ */
+struct handshake_req *handshake_req_alloc(const struct handshake_proto *proto,
+					  gfp_t flags)
+{
+	struct handshake_req *req;
+
+	if (!proto)
+		return NULL;
+	if (proto->hp_handler_class <= HANDSHAKE_HANDLER_CLASS_NONE)
+		return NULL;
+	if (proto->hp_handler_class >= HANDSHAKE_HANDLER_CLASS_MAX)
+		return NULL;
+	if (!proto->hp_accept || !proto->hp_done)
+		return NULL;
+
+	req = kzalloc(struct_size(req, hr_priv, proto->hp_privsize), flags);
+	if (!req)
+		return NULL;
+
+	INIT_LIST_HEAD(&req->hr_list);
+	req->hr_proto = proto;
+	return req;
+}
+EXPORT_SYMBOL(handshake_req_alloc);
+
+/**
+ * handshake_req_private - Get 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 (WARN_ON_ONCE(!list_empty(&req->hr_list)))
+		return false;
+	hn->hn_pending++;
+	list_add_tail(&req->hr_list, &hn->hn_requests);
+	return true;
+}
+
+static 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 = false;
+
+	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;
+}
+
+struct handshake_req *handshake_req_next(struct handshake_net *hn, int class)
+{
+	struct handshake_req *req, *pos;
+
+	req = NULL;
+	spin_lock(&hn->hn_lock);
+	list_for_each_entry(pos, &hn->hn_requests, hr_list) {
+		if (pos->hr_proto->hp_handler_class != class)
+			continue;
+		__remove_pending_locked(hn, pos);
+		req = pos;
+		break;
+	}
+	spin_unlock(&hn->hn_lock);
+
+	return req;
+}
+
+/**
+ * handshake_req_submit - Submit a handshake request
+ * @sock: open socket on which to perform the handshake
+ * @req: handshake arguments
+ * @flags: memory allocation flags
+ *
+ * Return values:
+ *   %0: Request queued
+ *   %-EINVAL: Invalid argument
+ *   %-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_req_submit() means that
+ * exactly one subsequent completion callback is guaranteed.
+ *
+ * A negative return value from handshake_req_submit() means that
+ * no completion callback will be done and that @req has been
+ * destroyed.
+ */
+int handshake_req_submit(struct socket *sock, struct handshake_req *req,
+			 gfp_t flags)
+{
+	struct handshake_net *hn;
+	struct net *net;
+	int ret;
+
+	if (!sock || !req || !sock->file) {
+		kfree(req);
+		return -EINVAL;
+	}
+
+	req->hr_sk = sock->sk;
+	if (!req->hr_sk) {
+		kfree(req);
+		return -EINVAL;
+	}
+	req->hr_odestruct = req->hr_sk->sk_destruct;
+	req->hr_sk->sk_destruct = handshake_sk_destruct;
+
+	ret = -EOPNOTSUPP;
+	net = sock_net(req->hr_sk);
+	hn = handshake_pernet(net);
+	if (!hn)
+		goto out_err;
+
+	ret = -EAGAIN;
+	if (READ_ONCE(hn->hn_pending) >= hn->hn_pending_max)
+		goto out_err;
+
+	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, flags);
+	if (ret) {
+		trace_handshake_notify_err(net, req, req->hr_sk, ret);
+		if (remove_pending(hn, req))
+			goto out_err;
+	}
+
+	/* Prevent socket release while a handshake request is pending */
+	sock_hold(req->hr_sk);
+
+	trace_handshake_submit(net, req, req->hr_sk);
+	return 0;
+
+out_unlock:
+	spin_unlock(&hn->hn_lock);
+out_err:
+	trace_handshake_submit_err(net, req, req->hr_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);
+
+		/* Handshake request is no longer pending */
+		sock_put(sk);
+	}
+}
+
+/**
+ * handshake_req_cancel - Cancel an in-progress handshake
+ * @sk: socket on which there is an ongoing handshake
+ *
+ * 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
+ *   %false - Handshake request already completed or not found
+ */
+bool handshake_req_cancel(struct sock *sk)
+{
+	struct handshake_req *req;
+	struct handshake_net *hn;
+	struct net *net;
+
+	net = sock_net(sk);
+	req = handshake_req_hash_lookup(sk);
+	if (!req) {
+		trace_handshake_cancel_none(net, req, sk);
+		return false;
+	}
+
+	hn = handshake_pernet(net);
+	if (hn && remove_pending(hn, req)) {
+		/* Request hadn't been accepted */
+		goto out_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;
+	}
+
+out_true:
+	trace_handshake_cancel(net, req, sk);
+
+	/* Handshake request is no longer pending */
+	sock_put(sk);
+	return true;
+}
+EXPORT_SYMBOL(handshake_req_cancel);