1 /*
2 * Copyright (C) 2012-2014 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 #include <limits.h>
18 #include <sys/cdefs.h>
19 #include <sys/prctl.h>
20 #include <sys/socket.h>
21 #include <sys/types.h>
22 #include <sys/un.h>
23 #include <unistd.h>
24
25 #include <thread>
26
27 #include <cutils/sockets.h>
28 #include <private/android_filesystem_config.h>
29 #include <private/android_logger.h>
30
31 #include "LogBuffer.h"
32 #include "LogListener.h"
33 #include "LogPermissions.h"
34
LogListener(LogBuffer * buf)35 LogListener::LogListener(LogBuffer* buf) : socket_(GetLogSocket()), logbuf_(buf) {}
36
StartListener()37 bool LogListener::StartListener() {
38 if (socket_ <= 0) {
39 return false;
40 }
41 auto thread = std::thread(&LogListener::ThreadFunction, this);
42 thread.detach();
43 return true;
44 }
45
ThreadFunction()46 void LogListener::ThreadFunction() {
47 prctl(PR_SET_NAME, "logd.writer");
48
49 while (true) {
50 HandleData();
51 }
52 }
53
HandleData()54 void LogListener::HandleData() {
55 // + 1 to ensure null terminator if MAX_PAYLOAD buffer is received
56 __attribute__((uninitialized)) char
57 buffer[sizeof(android_log_header_t) + LOGGER_ENTRY_MAX_PAYLOAD + 1];
58 struct iovec iov = {buffer, sizeof(buffer) - 1};
59
60 alignas(4) char control[CMSG_SPACE(sizeof(struct ucred))];
61 struct msghdr hdr = {
62 nullptr, 0, &iov, 1, control, sizeof(control), 0,
63 };
64
65 ssize_t n = recvmsg(socket_, &hdr, 0);
66 if (n <= (ssize_t)(sizeof(android_log_header_t))) {
67 return;
68 }
69
70 // To clear the entire buffer would be safe, but this contributes to 1.68%
71 // overhead under logging load. We are safe because we check counts, but
72 // still need to clear null terminator
73 buffer[n] = 0;
74
75 struct ucred* cred = nullptr;
76
77 struct cmsghdr* cmsg = CMSG_FIRSTHDR(&hdr);
78 while (cmsg != nullptr) {
79 if (cmsg->cmsg_level == SOL_SOCKET &&
80 cmsg->cmsg_type == SCM_CREDENTIALS) {
81 cred = (struct ucred*)CMSG_DATA(cmsg);
82 break;
83 }
84 cmsg = CMSG_NXTHDR(&hdr, cmsg);
85 }
86
87 if (cred == nullptr) {
88 return;
89 }
90
91 if (cred->uid == AID_LOGD) {
92 // ignore log messages we send to ourself.
93 // Such log messages are often generated by libraries we depend on
94 // which use standard Android logging.
95 return;
96 }
97
98 android_log_header_t* header =
99 reinterpret_cast<android_log_header_t*>(buffer);
100 log_id_t logId = static_cast<log_id_t>(header->id);
101 if (/* logId < LOG_ID_MIN || */ logId >= LOG_ID_MAX ||
102 logId == LOG_ID_KERNEL) {
103 return;
104 }
105
106 if (logId == LOG_ID_SECURITY) {
107 if (!__android_log_security()) {
108 return;
109 }
110 if (!clientCanWriteSecurityLog(cred->uid, cred->gid, cred->pid)) {
111 return;
112 }
113 }
114
115 char* msg = ((char*)buffer) + sizeof(android_log_header_t);
116 n -= sizeof(android_log_header_t);
117
118 // NB: hdr.msg_flags & MSG_TRUNC is not tested, silently passing a
119 // truncated message to the logs.
120
121 logbuf_->Log(logId, header->realtime, cred->uid, cred->pid, header->tid, msg,
122 ((size_t)n <= UINT16_MAX) ? (uint16_t)n : UINT16_MAX);
123 }
124
GetLogSocket()125 int LogListener::GetLogSocket() {
126 static const char socketName[] = "logdw";
127 int sock = android_get_control_socket(socketName);
128
129 if (sock < 0) { // logd started up in init.sh
130 sock = socket_local_server(
131 socketName, ANDROID_SOCKET_NAMESPACE_RESERVED, SOCK_DGRAM);
132
133 int on = 1;
134 if (setsockopt(sock, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on))) {
135 return -1;
136 }
137 }
138 return sock;
139 }
140