1 /*
2 * Copyright (C) 2016 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 <errno.h>
18 #include <signal.h>
19 #include <stdlib.h>
20 #include <string.h>
21 #include <sys/socket.h>
22 #include <sys/syscall.h>
23 #include <sys/types.h>
24 #include <sys/wait.h>
25 #include <unistd.h>
26
27 #include <log/logger.h>
28
29 #include "signal_sender.h"
30
31 static int signal_fd = -1;
32 static pid_t signal_pid;
33 struct signal_message {
34 pid_t pid;
35 pid_t tid;
36 int signal;
37 };
38
set_signal_sender_process_name()39 static void set_signal_sender_process_name() {
40 #if defined(__LP64__)
41 static constexpr char long_process_name[] = "debuggerd64:signaller";
42 static constexpr char short_process_name[] = "debuggerd64:sig";
43 static_assert(sizeof(long_process_name) <= sizeof("/system/bin/debuggerd64"), "");
44 #else
45 static constexpr char long_process_name[] = "debuggerd:signaller";
46 static constexpr char short_process_name[] = "debuggerd:sig";
47 static_assert(sizeof(long_process_name) <= sizeof("/system/bin/debuggerd"), "");
48 #endif
49
50 // pthread_setname_np has a maximum length of 16 chars, including null terminator.
51 static_assert(sizeof(short_process_name) <= 16, "");
52 pthread_setname_np(pthread_self(), short_process_name);
53
54 char* progname = const_cast<char*>(getprogname());
55 if (strlen(progname) <= strlen(long_process_name)) {
56 ALOGE("debuggerd: unexpected progname %s", progname);
57 return;
58 }
59
60 memset(progname, 0, strlen(progname));
61 strcpy(progname, long_process_name);
62 }
63
64 // Fork a process to send signals for the worker processes to use after they've dropped privileges.
start_signal_sender()65 bool start_signal_sender() {
66 if (signal_pid != 0) {
67 ALOGE("debuggerd: attempted to start signal sender multiple times");
68 return false;
69 }
70
71 int sfd[2];
72 if (socketpair(AF_UNIX, SOCK_SEQPACKET | SOCK_CLOEXEC, 0, sfd) != 0) {
73 ALOGE("debuggerd: failed to create socketpair for signal sender: %s", strerror(errno));
74 return false;
75 }
76
77 pid_t parent = getpid();
78 pid_t fork_pid = fork();
79 if (fork_pid == -1) {
80 ALOGE("debuggerd: failed to initialize signal sender: fork failed: %s", strerror(errno));
81 return false;
82 } else if (fork_pid == 0) {
83 close(sfd[1]);
84
85 set_signal_sender_process_name();
86
87 while (true) {
88 signal_message msg;
89 int rc = TEMP_FAILURE_RETRY(read(sfd[0], &msg, sizeof(msg)));
90 if (rc < 0) {
91 ALOGE("debuggerd: signal sender failed to read from socket");
92 break;
93 } else if (rc != sizeof(msg)) {
94 ALOGE("debuggerd: signal sender read unexpected number of bytes: %d", rc);
95 break;
96 }
97
98 // Report success after sending a signal
99 int err = 0;
100 if (msg.tid > 0) {
101 if (syscall(SYS_tgkill, msg.pid, msg.tid, msg.signal) != 0) {
102 err = errno;
103 }
104 } else {
105 if (kill(msg.pid, msg.signal) != 0) {
106 err = errno;
107 }
108 }
109
110 if (TEMP_FAILURE_RETRY(write(sfd[0], &err, sizeof(err))) < 0) {
111 ALOGE("debuggerd: signal sender failed to write: %s", strerror(errno));
112 }
113 }
114
115 // Our parent proably died, but if not, kill them.
116 if (getppid() == parent) {
117 kill(parent, SIGKILL);
118 }
119 _exit(1);
120 } else {
121 close(sfd[0]);
122 signal_fd = sfd[1];
123 signal_pid = fork_pid;
124 return true;
125 }
126 }
127
stop_signal_sender()128 bool stop_signal_sender() {
129 if (signal_pid <= 0) {
130 return false;
131 }
132
133 if (kill(signal_pid, SIGKILL) != 0) {
134 ALOGE("debuggerd: failed to kill signal sender: %s", strerror(errno));
135 return false;
136 }
137
138 close(signal_fd);
139 signal_fd = -1;
140
141 int status;
142 waitpid(signal_pid, &status, 0);
143 signal_pid = 0;
144
145 return true;
146 }
147
send_signal(pid_t pid,pid_t tid,int signal)148 bool send_signal(pid_t pid, pid_t tid, int signal) {
149 if (signal_fd == -1) {
150 ALOGE("debuggerd: attempted to send signal before signal sender was started");
151 errno = EHOSTUNREACH;
152 return false;
153 }
154
155 signal_message msg = {.pid = pid, .tid = tid, .signal = signal };
156 if (TEMP_FAILURE_RETRY(write(signal_fd, &msg, sizeof(msg))) < 0) {
157 ALOGE("debuggerd: failed to send message to signal sender: %s", strerror(errno));
158 errno = EHOSTUNREACH;
159 return false;
160 }
161
162 int response;
163 ssize_t rc = TEMP_FAILURE_RETRY(read(signal_fd, &response, sizeof(response)));
164 if (rc == 0) {
165 ALOGE("debuggerd: received EOF from signal sender");
166 errno = EHOSTUNREACH;
167 return false;
168 } else if (rc < 0) {
169 ALOGE("debuggerd: failed to receive response from signal sender: %s", strerror(errno));
170 errno = EHOSTUNREACH;
171 return false;
172 }
173
174 if (response == 0) {
175 return true;
176 }
177
178 errno = response;
179 return false;
180 }
181