1 /*
2  * Copyright (C) 2017 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 #pragma once
18 
19 #include <functional>
20 #include <linux/netlink.h>
21 #include <linux/rtnetlink.h>
22 
23 #include "NetdConstants.h"
24 
25 namespace android::net {
26 
27 const sockaddr_nl KERNEL_NLADDR = {AF_NETLINK, 0, 0, 0};
28 
29 const uint16_t NETLINK_REQUEST_FLAGS = NLM_F_REQUEST | NLM_F_ACK;
30 const uint16_t NETLINK_ROUTE_CREATE_FLAGS = NETLINK_REQUEST_FLAGS | NLM_F_CREATE | NLM_F_EXCL;
31 const uint16_t NETLINK_ROUTE_REPLACE_FLAGS = NETLINK_REQUEST_FLAGS | NLM_F_REPLACE;
32 // Don't create rules with NLM_F_EXCL, because operations such as changing network permissions rely
33 // on make-before-break. The kernel did not complain about duplicate rules until ~4.9, at which
34 // point it started returning EEXIST. See for example b/69607866 . We can't just ignore the EEXIST
35 // because if we hit it, the rule was not created, but we will think it was, and we'll then trip up
36 // trying to delete it.
37 const uint16_t NETLINK_RULE_CREATE_FLAGS = NETLINK_REQUEST_FLAGS | NLM_F_CREATE;
38 const uint16_t NETLINK_DUMP_FLAGS = NLM_F_REQUEST | NLM_F_DUMP;
39 
40 // Generic code for processing netlink dumps.
41 const int kNetlinkDumpBufferSize = 8192;
42 typedef std::function<void(nlmsghdr *)> NetlinkDumpCallback;
43 typedef std::function<bool(nlmsghdr *)> NetlinkDumpFilter;
44 
45 // Opens an RTNetlink socket and connects it to the kernel.
46 [[nodiscard]] int openNetlinkSocket(int protocol);
47 
48 // Receives a netlink ACK. Returns 0 if the command succeeded or negative errno if the command
49 // failed or receiving the ACK failed.
50 [[nodiscard]] int recvNetlinkAck(int sock);
51 
52 // Sends a netlink request and possibly expects an ACK. The first element of iov should be null and
53 // will be set to the netlink message headerheader. The subsequent elements are the contents of the
54 // request.
55 [[nodiscard]] int sendNetlinkRequest(uint16_t action, uint16_t flags, iovec* iov, int iovlen,
56                                      const NetlinkDumpCallback* callback);
57 
58 // Processes a netlink dump, passing every message to the specified |callback|.
59 [[nodiscard]] int processNetlinkDump(int sock, const NetlinkDumpCallback& callback);
60 
61 // Flushes netlink objects that take an rtmsg structure (FIB rules, routes...). |getAction| and
62 // |deleteAction| specify the netlink message types, e.g., RTM_GETRULE and RTM_DELRULE.
63 // |shouldDelete| specifies whether a given object should be deleted or not. |what| is a
64 // human-readable name for the objects being flushed, e.g. "rules".
65 [[nodiscard]] int rtNetlinkFlush(uint16_t getAction, uint16_t deleteAction, const char* what,
66                                  const NetlinkDumpFilter& shouldDelete);
67 
68 // Returns the value of the specific __u32 attribute, or 0 if the attribute was not present.
69 uint32_t getRtmU32Attribute(const nlmsghdr *nlh, int attribute);
70 
71 }  // namespace android::net
72