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 // To clear the entire buffer is secure/safe, but this contributes to 1.68%
66 // overhead under logging load. We are safe because we check counts, but
67 // still need to clear null terminator
68 // memset(buffer, 0, sizeof(buffer));
69 ssize_t n = recvmsg(socket_, &hdr, 0);
70 if (n <= (ssize_t)(sizeof(android_log_header_t))) {
71 return;
72 }
73
74 buffer[n] = 0;
75
76 struct ucred* cred = nullptr;
77
78 struct cmsghdr* cmsg = CMSG_FIRSTHDR(&hdr);
79 while (cmsg != nullptr) {
80 if (cmsg->cmsg_level == SOL_SOCKET &&
81 cmsg->cmsg_type == SCM_CREDENTIALS) {
82 cred = (struct ucred*)CMSG_DATA(cmsg);
83 break;
84 }
85 cmsg = CMSG_NXTHDR(&hdr, cmsg);
86 }
87
88 if (cred == nullptr) {
89 return;
90 }
91
92 if (cred->uid == AID_LOGD) {
93 // ignore log messages we send to ourself.
94 // Such log messages are often generated by libraries we depend on
95 // which use standard Android logging.
96 return;
97 }
98
99 android_log_header_t* header =
100 reinterpret_cast<android_log_header_t*>(buffer);
101 log_id_t logId = static_cast<log_id_t>(header->id);
102 if (/* logId < LOG_ID_MIN || */ logId >= LOG_ID_MAX ||
103 logId == LOG_ID_KERNEL) {
104 return;
105 }
106
107 if ((logId == LOG_ID_SECURITY) &&
108 (!__android_log_security() ||
109 !clientHasLogCredentials(cred->uid, cred->gid, cred->pid))) {
110 return;
111 }
112
113 char* msg = ((char*)buffer) + sizeof(android_log_header_t);
114 n -= sizeof(android_log_header_t);
115
116 // NB: hdr.msg_flags & MSG_TRUNC is not tested, silently passing a
117 // truncated message to the logs.
118
119 logbuf_->Log(logId, header->realtime, cred->uid, cred->pid, header->tid, msg,
120 ((size_t)n <= UINT16_MAX) ? (uint16_t)n : UINT16_MAX);
121 }
122
GetLogSocket()123 int LogListener::GetLogSocket() {
124 static const char socketName[] = "logdw";
125 int sock = android_get_control_socket(socketName);
126
127 if (sock < 0) { // logd started up in init.sh
128 sock = socket_local_server(
129 socketName, ANDROID_SOCKET_NAMESPACE_RESERVED, SOCK_DGRAM);
130
131 int on = 1;
132 if (setsockopt(sock, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on))) {
133 return -1;
134 }
135 }
136 return sock;
137 }
138