debuggerd: fork the signal sender once.
Bug: http://b/27427439
Change-Id: I6294ff68a150bc9950a300264c31d2141307ac66
diff --git a/debuggerd/signal_sender.cpp b/debuggerd/signal_sender.cpp
new file mode 100644
index 0000000..35e0c0b
--- /dev/null
+++ b/debuggerd/signal_sender.cpp
@@ -0,0 +1,152 @@
+/*
+ * 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.
+ */
+
+#include <errno.h>
+#include <signal.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/logger.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;
+};
+
+// 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]);
+
+ 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;
+}