flow_dissector: Move out netns_bpf prog callbacks

Move functions to manage BPF programs attached to netns that are not
specific to flow dissector to a dedicated module named
bpf/net_namespace.c.

The set of functions will grow with the addition of bpf_link support for
netns attached programs. This patch prepares ground by creating a place
for it.

This is a code move with no functional changes intended.

Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200531082846.2117903-4-jakub@cloudflare.com

kernel/bpf/net_namespace.c

@@ -0,0 +1,133 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bpf.h>
+#include <linux/filter.h>
+#include <net/net_namespace.h>
+
+/*
+ * Functions to manage BPF programs attached to netns
+ */
+
+/* Protects updates to netns_bpf */
+DEFINE_MUTEX(netns_bpf_mutex);
+
+int netns_bpf_prog_query(const union bpf_attr *attr,
+			 union bpf_attr __user *uattr)
+{
+	__u32 __user *prog_ids = u64_to_user_ptr(attr->query.prog_ids);
+	u32 prog_id, prog_cnt = 0, flags = 0;
+	enum netns_bpf_attach_type type;
+	struct bpf_prog *attached;
+	struct net *net;
+
+	if (attr->query.query_flags)
+		return -EINVAL;
+
+	type = to_netns_bpf_attach_type(attr->query.attach_type);
+	if (type < 0)
+		return -EINVAL;
+
+	net = get_net_ns_by_fd(attr->query.target_fd);
+	if (IS_ERR(net))
+		return PTR_ERR(net);
+
+	rcu_read_lock();
+	attached = rcu_dereference(net->bpf.progs[type]);
+	if (attached) {
+		prog_cnt = 1;
+		prog_id = attached->aux->id;
+	}
+	rcu_read_unlock();
+
+	put_net(net);
+
+	if (copy_to_user(&uattr->query.attach_flags, &flags, sizeof(flags)))
+		return -EFAULT;
+	if (copy_to_user(&uattr->query.prog_cnt, &prog_cnt, sizeof(prog_cnt)))
+		return -EFAULT;
+
+	if (!attr->query.prog_cnt || !prog_ids || !prog_cnt)
+		return 0;
+
+	if (copy_to_user(prog_ids, &prog_id, sizeof(u32)))
+		return -EFAULT;
+
+	return 0;
+}
+
+int netns_bpf_prog_attach(const union bpf_attr *attr, struct bpf_prog *prog)
+{
+	enum netns_bpf_attach_type type;
+	struct net *net;
+	int ret;
+
+	type = to_netns_bpf_attach_type(attr->attach_type);
+	if (type < 0)
+		return -EINVAL;
+
+	net = current->nsproxy->net_ns;
+	mutex_lock(&netns_bpf_mutex);
+	switch (type) {
+	case NETNS_BPF_FLOW_DISSECTOR:
+		ret = flow_dissector_bpf_prog_attach(net, prog);
+		break;
+	default:
+		ret = -EINVAL;
+		break;
+	}
+	mutex_unlock(&netns_bpf_mutex);
+
+	return ret;
+}
+
+/* Must be called with netns_bpf_mutex held. */
+static int __netns_bpf_prog_detach(struct net *net,
+				   enum netns_bpf_attach_type type)
+{
+	struct bpf_prog *attached;
+
+	attached = rcu_dereference_protected(net->bpf.progs[type],
+					     lockdep_is_held(&netns_bpf_mutex));
+	if (!attached)
+		return -ENOENT;
+	RCU_INIT_POINTER(net->bpf.progs[type], NULL);
+	bpf_prog_put(attached);
+	return 0;
+}
+
+int netns_bpf_prog_detach(const union bpf_attr *attr)
+{
+	enum netns_bpf_attach_type type;
+	int ret;
+
+	type = to_netns_bpf_attach_type(attr->attach_type);
+	if (type < 0)
+		return -EINVAL;
+
+	mutex_lock(&netns_bpf_mutex);
+	ret = __netns_bpf_prog_detach(current->nsproxy->net_ns, type);
+	mutex_unlock(&netns_bpf_mutex);
+
+	return ret;
+}
+
+static void __net_exit netns_bpf_pernet_pre_exit(struct net *net)
+{
+	enum netns_bpf_attach_type type;
+
+	mutex_lock(&netns_bpf_mutex);
+	for (type = 0; type < MAX_NETNS_BPF_ATTACH_TYPE; type++)
+		__netns_bpf_prog_detach(net, type);
+	mutex_unlock(&netns_bpf_mutex);
+}
+
+static struct pernet_operations netns_bpf_pernet_ops __net_initdata = {
+	.pre_exit = netns_bpf_pernet_pre_exit,
+};
+
+static int __init netns_bpf_init(void)
+{
+	return register_pernet_subsys(&netns_bpf_pernet_ops);
+}
+
+subsys_initcall(netns_bpf_init);