debuggerd: fork the signal sender once. (f5e8f0b9) · Commits · e / os / android_system_core

debuggerd/Android.mk

+1 −0

Original line number	Diff line number	Diff line
		@@ -15,6 +15,7 @@ LOCAL_SRC_FILES:= \
		debuggerd.cpp \
		elf_utils.cpp \
		getevent.cpp \
		signal_sender.cpp \
		tombstone.cpp \
		utility.cpp \

debuggerd/debuggerd.cpp

+14 −91

Original line number	Diff line number	Diff line
		@@ -15,21 +15,20 @@
		*/

		#include <dirent.h>
		#include <elf.h>
		#include <errno.h>
		#include <fcntl.h>
		#include <pthread.h>
		#include <signal.h>
		#include <stdarg.h>
		#include <stdio.h>
		#include <sys/types.h>
		#include <time.h>

		#include <elf.h>
		#include <sys/poll.h>
		#include <sys/prctl.h>
		#include <sys/ptrace.h>
		#include <sys/stat.h>
		#include <sys/types.h>
		#include <sys/wait.h>
		#include <time.h>

		#include <set>

		@@ -48,6 +47,7 @@

		#include "backtrace.h"
		#include "getevent.h"
		#include "signal_sender.h"
		#include "tombstone.h"
		#include "utility.h"

		@@ -422,7 +422,7 @@ static bool perform_dump(const debugger_request_t& request, int fd, int tombston
		// this we get a lot of "ptrace detach failed:
		// No such process".
		*crash_signal = signal;
		kill(request.pid, SIGSTOP);
		send_signal(request.pid, 0, SIGSTOP);
		engrave_tombstone(tombstone_fd, backtrace_map, request.pid, request.tid, siblings, signal,
		request.original_si_code, request.abort_msg_address);
		break;
		@@ -451,60 +451,6 @@ static bool drop_privileges() {
		return true;
		}

		// Fork a process that listens for signals to send, or 0, to exit.
		static bool fork_signal_sender(int* out_fd, pid_t* sender_pid, pid_t target_pid) {
		int sfd[2];
		if (socketpair(AF_UNIX, SOCK_SEQPACKET, 0, sfd) != 0) {
		ALOGE("debuggerd: failed to create socketpair for signal sender: %s", strerror(errno));
		return false;
		}

		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) {
		int signal;
		int rc = TEMP_FAILURE_RETRY(read(sfd[0], &signal, sizeof(signal)));
		if (rc < 0) {
		ALOGE("debuggerd: signal sender failed to read from socket");
		kill(target_pid, SIGKILL);
		exit(1);
		} else if (rc != sizeof(signal)) {
		ALOGE("debuggerd: signal sender read unexpected number of bytes: %d", rc);
		kill(target_pid, SIGKILL);
		exit(1);
		}

		// Report success after sending a signal, or before exiting.
		int err = 0;
		if (signal != 0) {
		if (kill(target_pid, 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));
		kill(target_pid, SIGKILL);
		exit(1);
		}

		if (signal == 0) {
		exit(0);
		}
		}
		} else {
		close(sfd[0]);
		*out_fd = sfd[1];
		*sender_pid = fork_pid;
		return true;
		}
		}

		static void handle_request(int fd) {
		ALOGV("handle_request(%d)\n", fd);

		@@ -585,15 +531,6 @@ static void handle_request(int fd) {
		// Don't attach to the sibling threads if we want to attach gdb.
		// Supposedly, it makes the process less reliable.
		bool attach_gdb = should_attach_gdb(&request);
		int signal_fd = -1;
		pid_t signal_pid = 0;

		// Fork a process that stays root, and listens on a pipe to pause and resume the target.
		if (!fork_signal_sender(&signal_fd, &signal_pid, request.pid)) {
		ALOGE("debuggerd: failed to fork signal sender");
		exit(1);
		}

		if (attach_gdb) {
		// Open all of the input devices we need to listen for VOLUMEDOWN before dropping privileges.
		if (init_getevent() != 0) {
		@@ -603,21 +540,6 @@ static void handle_request(int fd) {

		}

		auto send_signal = [=](int signal) {
		int error;
		if (TEMP_FAILURE_RETRY(write(signal_fd, &signal, sizeof(signal))) < 0) {
		ALOGE("debuggerd: failed to notify signal process: %s", strerror(errno));
		return false;
		} else if (TEMP_FAILURE_RETRY(read(signal_fd, &error, sizeof(error))) < 0) {
		ALOGE("debuggerd: failed to read response from signal process: %s", strerror(errno));
		return false;
		} else if (error != 0) {
		errno = error;
		return false;
		}
		return true;
		};

		std::set<pid_t> siblings;
		if (!attach_gdb) {
		ptrace_siblings(request.pid, request.tid, siblings);
		@@ -646,7 +568,7 @@ static void handle_request(int fd) {

		if (attach_gdb) {
		// Tell the signal process to send SIGSTOP to the target.
		if (!send_signal(SIGSTOP)) {
		if (!send_signal(request.pid, 0, SIGSTOP)) {
		ALOGE("debuggerd: failed to stop process for gdb attach: %s", strerror(errno));
		attach_gdb = false;
		}
		@@ -662,7 +584,7 @@ static void handle_request(int fd) {

		// Send the signal back to the process if it crashed and we're not waiting for gdb.
		if (!attach_gdb && request.action == DEBUGGER_ACTION_CRASH) {
		if (!send_signal(crash_signal)) {
		if (!send_signal(request.pid, request.tid, crash_signal)) {
		ALOGE("debuggerd: failed to kill process %d: %s", request.pid, strerror(errno));
		}
		}
		@@ -672,18 +594,13 @@ static void handle_request(int fd) {
		wait_for_user_action(request);

		// Tell the signal process to send SIGCONT to the target.
		if (!send_signal(SIGCONT)) {
		if (!send_signal(request.pid, 0, SIGCONT)) {
		ALOGE("debuggerd: failed to resume process %d: %s", request.pid, strerror(errno));
		}

		uninit_getevent();
		}

		if (!send_signal(0)) {
		ALOGE("debuggerd: failed to notify signal sender to finish");
		kill(signal_pid, SIGKILL);
		}
		waitpid(signal_pid, nullptr, 0);
		exit(!succeeded);
		}

		@@ -714,6 +631,12 @@ static int do_server() {
		SOCK_STREAM \| SOCK_CLOEXEC);
		if (s == -1) return 1;

		// Fork a process that stays root, and listens on a pipe to pause and resume the target.
		if (!start_signal_sender()) {
		ALOGE("debuggerd: failed to fork signal sender");
		return 1;
		}

		ALOGI("debuggerd: starting\n");

		for (;;) {

debuggerd/signal_sender.cpp

0 → 100644

+152 −0

Original line number	Diff line number	Diff line
		/*
		* 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;
		}

debuggerd/signal_sender.h

0 → 100644

+30 −0

Original line number	Diff line number	Diff line
		/*
		* 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.
		*/

		#ifndef _DEBUGGERD_SIGNAL_SENDER_H
		#define _DEBUGGERD_SIGNAL_SENDER_H

		#include <sys/types.h>

		bool start_signal_sender();
		bool stop_signal_sender();

		// Sends a signal to a target process or thread.
		// If tid is greater than zero, this performs tgkill(pid, tid, signal).
		// Otherwise, it performs kill(pid, signal).
		bool send_signal(pid_t pid, pid_t tid, int signal);

		#endif