[NETD-BPF#19] Mainline part of bpf code from netd

1. Add libnetd_updatable.so in com.android.tethering. The library is
loaded by netd. Currently, it mainly targets on a few functions which
access BPF maps. The functionality may extend in the future.

2. Attach gcroup progs from libnetd_updatable.so.

3. Move (privileged)TagSocket and untagSocket implementation to mainline
module. Combine privilegedTagSocket and untagSocket into a single
function.

4. Split related unit tests from netd_unit_test to
libnetd_updatable_unit_test as well.

Bug: 202086915
Test: cd system/netd; atest
Test: atest TrafficStatsTest NetworkUsageStatsTest

Change-Id: Ib556458103a4cbb643c1342d9b689ac692160de0

netd/include/NetdUpdatablePublic.h

@@ -0,0 +1,61 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <stdint.h>
+#include <sys/cdefs.h>
+#include <sys/types.h>
+
+__BEGIN_DECLS
+
+/*
+ * Initial function for libnetd_updatable library.
+ *
+ * The function uses |cg2_path| as cgroup v2 mount location to attach BPF programs so that the
+ * kernel can record packet number, size, etc. in BPF maps when packets pass through, and let user
+ * space retrieve statistics.
+ *
+ * Returns 0 on success, or a negative POSIX error code (see errno.h) on
+ * failure.
+ */
+int libnetd_updatable_init(const char* cg2_path);
+
+/*
+ * Set the socket tag and owning UID for traffic statistics on the specified socket. Permission
+ * check is performed based on the |realUid| before socket tagging.
+ *
+ * The |sockFd| is a file descriptor of the socket that needs to tag. The |tag| is the mark to tag.
+ * It can be an arbitrary value in uint32_t range. The |chargeUid| is owning uid which will be
+ * tagged along with the |tag|. The |realUid| is an effective uid of the calling process, which is
+ * used for permission check before socket tagging.
+ *
+ * Returns 0 on success, or a negative POSIX error code (see errno.h) on failure.
+ */
+int libnetd_updatable_tagSocket(int sockFd, uint32_t tag, uid_t chargeUid,
+                                                       uid_t realUid);
+
+/*
+ * Untag a network socket. Future traffic on this socket will no longer be associated with any
+ * previously configured tag and uid.
+ *
+ * The |sockFd| is a file descriptor of the socket that wants to untag.
+ *
+ * Returns 0 on success, or a negative POSIX error code (see errno.h) on failure.
+ */
+int libnetd_updatable_untagSocket(int sockFd);
+
+__END_DECLS