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/*
* Copyright (C) 2016 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.
*/
#define LOG_TAG "debuggerd-signal"
#include <errno.h>
#include <pthread.h>
#include <signal.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <log/log.h>
#include "signal_sender.h"
static int signal_fd = -1;
static pid_t signal_pid;
struct signal_message {
pid_t pid;
pid_t tid;
int signal;
};
static void set_signal_sender_process_name() {
#if defined(__LP64__)
static constexpr char long_process_name[] = "debuggerd64:signaller";
static constexpr char short_process_name[] = "debuggerd64:sig";
static_assert(sizeof(long_process_name) <= sizeof("/system/bin/debuggerd64"), "");
#else
static constexpr char long_process_name[] = "debuggerd:signaller";
static constexpr char short_process_name[] = "debuggerd:sig";
static_assert(sizeof(long_process_name) <= sizeof("/system/bin/debuggerd"), "");
#endif
// pthread_setname_np has a maximum length of 16 chars, including null terminator.
static_assert(sizeof(short_process_name) <= 16, "");
pthread_setname_np(pthread_self(), short_process_name);
char* progname = const_cast<char*>(getprogname());
if (strlen(progname) <= strlen(long_process_name)) {
ALOGE("debuggerd: unexpected progname %s", progname);
return;
}
memset(progname, 0, strlen(progname));
strcpy(progname, long_process_name);
}
// Fork a process to send signals for the worker processes to use after they've dropped privileges.
bool start_signal_sender() {
if (signal_pid != 0) {
ALOGE("debuggerd: attempted to start signal sender multiple times");
return false;
}
int sfd[2];
if (socketpair(AF_UNIX, SOCK_SEQPACKET | SOCK_CLOEXEC, 0, sfd) != 0) {
ALOGE("debuggerd: failed to create socketpair for signal sender: %s", strerror(errno));
return false;
}
pid_t parent = getpid();
pid_t fork_pid = fork();
if (fork_pid == -1) {
ALOGE("debuggerd: failed to initialize signal sender: fork failed: %s", strerror(errno));
return false;
} else if (fork_pid == 0) {
close(sfd[1]);
set_signal_sender_process_name();
while (true) {
signal_message msg;
int rc = TEMP_FAILURE_RETRY(read(sfd[0], &msg, sizeof(msg)));
if (rc < 0) {
ALOGE("debuggerd: signal sender failed to read from socket");
break;
} else if (rc != sizeof(msg)) {
ALOGE("debuggerd: signal sender read unexpected number of bytes: %d", rc);
break;
}
// Report success after sending a signal
int err = 0;
if (msg.tid > 0) {
if (syscall(SYS_tgkill, msg.pid, msg.tid, msg.signal) != 0) {
err = errno;
}
} else {
if (kill(msg.pid, msg.signal) != 0) {
err = errno;
}
}
if (TEMP_FAILURE_RETRY(write(sfd[0], &err, sizeof(err))) < 0) {
ALOGE("debuggerd: signal sender failed to write: %s", strerror(errno));
}
}
// Our parent proably died, but if not, kill them.
if (getppid() == parent) {
kill(parent, SIGKILL);
}
_exit(1);
} else {
close(sfd[0]);
signal_fd = sfd[1];
signal_pid = fork_pid;
return true;
}
}
bool stop_signal_sender() {
if (signal_pid <= 0) {
return false;
}
if (kill(signal_pid, SIGKILL) != 0) {
ALOGE("debuggerd: failed to kill signal sender: %s", strerror(errno));
return false;
}
close(signal_fd);
signal_fd = -1;
int status;
waitpid(signal_pid, &status, 0);
signal_pid = 0;
return true;
}
bool send_signal(pid_t pid, pid_t tid, int signal) {
if (signal_fd == -1) {
ALOGE("debuggerd: attempted to send signal before signal sender was started");
errno = EHOSTUNREACH;
return false;
}
signal_message msg = {.pid = pid, .tid = tid, .signal = signal };
if (TEMP_FAILURE_RETRY(write(signal_fd, &msg, sizeof(msg))) < 0) {
ALOGE("debuggerd: failed to send message to signal sender: %s", strerror(errno));
errno = EHOSTUNREACH;
return false;
}
int response;
ssize_t rc = TEMP_FAILURE_RETRY(read(signal_fd, &response, sizeof(response)));
if (rc == 0) {
ALOGE("debuggerd: received EOF from signal sender");
errno = EHOSTUNREACH;
return false;
} else if (rc < 0) {
ALOGE("debuggerd: failed to receive response from signal sender: %s", strerror(errno));
errno = EHOSTUNREACH;
return false;
}
if (response == 0) {
return true;
}
errno = response;
return false;
}
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