debuggerd: advance our amazing bet.

Remove debuggerd in favor of a helper process that gets execed by
crashing processes.

Bug: http://b/30705528
Test: debuggerd_test
Change-Id: I9906c69473989cbf7fe5ea6cccf9a9c563d75906

1 files changed, 41 insertions, 910 deletions

diff --git a/debuggerd/debuggerd.cpp b/debuggerd/debuggerd.cpp
index 893adc860..320823082 100644
--- a/debuggerd/debuggerd.cpp
+++ b/debuggerd/debuggerd.cpp
@@ -1,5 +1,5 @@
 /*
- * Copyright 2006, The Android Open Source Project
+ * Copyright 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.
@@ -14,937 +14,68 @@
  * limitations under the License.
  */
 
-#define LOG_TAG "debuggerd"
-
-#include <arpa/inet.h>
-#include <dirent.h>
-#include <elf.h>
-#include <errno.h>
-#include <fcntl.h>
-#include <linux/input.h>
-#include <pthread.h>
-#include <signal.h>
-#include <stdarg.h>
+#include <err.h>
 #include <stdio.h>
-#include <sys/poll.h>
-#include <sys/prctl.h>
-#include <sys/ptrace.h>
-#include <sys/socket.h>
-#include <sys/stat.h>
-#include <sys/types.h>
-#include <sys/wait.h>
-#include <sys/un.h>
-#include <time.h>
-
-#include <memory>
-#include <set>
-#include <string>
+#include <stdlib.h>
+#include <string.h>
 
-#include <selinux/android.h>
+#include <limits>
+#include <thread>
 
 #include <android-base/file.h>
+#include <android-base/logging.h>
+#include <android-base/parseint.h>
 #include <android-base/unique_fd.h>
-#include <cutils/debugger.h>
-#include <cutils/properties.h>
-#include <cutils/sockets.h>
-#include <log/log.h>
-
-#include <private/android_filesystem_config.h>
-
 #include <debuggerd/client.h>
+#include <debuggerd/util.h>
+#include <selinux/selinux.h>
 
-#include "backtrace.h"
-#include "getevent.h"
-#include "open_files_list.h"
-#include "signal_sender.h"
-#include "tombstone.h"
-#include "utility.h"
-
-// If the 32 bit executable is compiled on a 64 bit system,
-// use the 32 bit socket name.
-#if defined(TARGET_IS_64_BIT) && !defined(__LP64__)
-#define SOCKET_NAME DEBUGGER32_SOCKET_NAME
-#else
-#define SOCKET_NAME DEBUGGER_SOCKET_NAME
-#endif
-
-struct debugger_request_t {
-  debugger_action_t action;
-  pid_t pid, tid;
-  uid_t uid, gid;
-  pid_t ignore_tid;
-  uintptr_t abort_msg_address;
-};
-
-static void wait_for_user_action(const debugger_request_t& request) {
-  // Explain how to attach the debugger.
-  ALOGI("***********************************************************\n"
-        "* Process %d has been suspended while crashing.\n"
-        "* To attach gdbserver and start gdb, run this on the host:\n"
-        "*\n"
-        "*     gdbclient.py -p %d\n"
-        "*\n"
-        "* Wait for gdb to start, then press the VOLUME DOWN key\n"
-        "* to let the process continue crashing.\n"
-        "***********************************************************",
-        request.pid, request.tid);
-
-  // Wait for VOLUME DOWN.
-  while (true) {
-    input_event e;
-    if (get_event(&e, -1) == 0) {
-      if (e.type == EV_KEY && e.code == KEY_VOLUMEDOWN && e.value == 0) {
-        break;
-      }
-    }
-  }
-
-  ALOGI("debuggerd resuming process %d", request.pid);
-}
-
-static int get_process_info(pid_t tid, pid_t* out_pid, uid_t* out_uid, uid_t* out_gid) {
-  char path[64];
-  snprintf(path, sizeof(path), "/proc/%d/status", tid);
-
-  FILE* fp = fopen(path, "r");
-  if (!fp) {
-    return -1;
-  }
+using android::base::unique_fd;
 
-  int fields = 0;
-  char line[1024];
-  while (fgets(line, sizeof(line), fp)) {
-    size_t len = strlen(line);
-    if (len > 6 && !memcmp(line, "Tgid:\t", 6)) {
-      *out_pid = atoi(line + 6);
-      fields |= 1;
-    } else if (len > 5 && !memcmp(line, "Uid:\t", 5)) {
-      *out_uid = atoi(line + 5);
-      fields |= 2;
-    } else if (len > 5 && !memcmp(line, "Gid:\t", 5)) {
-      *out_gid = atoi(line + 5);
-      fields |= 4;
-    }
-  }
-  fclose(fp);
-  return fields == 7 ? 0 : -1;
+static void usage(int exit_code) {
+  fprintf(stderr, "usage: debuggerd [-b] PID\n");
+  _exit(exit_code);
 }
 
-/*
- * Corresponds with debugger_action_t enum type in
- * include/cutils/debugger.h.
- */
-static const char *debuggerd_perms[] = {
-  NULL, /* crash is only used on self, no check applied */
-  "dump_tombstone",
-  "dump_backtrace"
-};
-
-static int audit_callback(void* data, security_class_t /* cls */, char* buf, size_t len)
-{
-    struct debugger_request_t* req = reinterpret_cast<debugger_request_t*>(data);
-
-    if (!req) {
-        ALOGE("No debuggerd request audit data");
-        return 0;
-    }
-
-    snprintf(buf, len, "pid=%d uid=%d gid=%d", req->pid, req->uid, req->gid);
-    return 0;
-}
-
-static bool selinux_action_allowed(int s, debugger_request_t* request)
-{
-  char *scon = NULL, *tcon = NULL;
-  const char *tclass = "debuggerd";
-  const char *perm;
-  bool allowed = false;
-
-  if (request->action <= 0 || request->action >= (sizeof(debuggerd_perms)/sizeof(debuggerd_perms[0]))) {
-    ALOGE("SELinux:  No permission defined for debugger action %d", request->action);
-    return false;
-  }
-
-  perm = debuggerd_perms[request->action];
-
-  if (getpeercon(s, &scon) < 0) {
-    ALOGE("Cannot get peer context from socket\n");
-    goto out;
-  }
-
-  if (getpidcon(request->tid, &tcon) < 0) {
-    ALOGE("Cannot get context for tid %d\n", request->tid);
-    goto out;
-  }
-
-  allowed = (selinux_check_access(scon, tcon, tclass, perm, reinterpret_cast<void*>(request)) == 0);
-
-out:
-   freecon(scon);
-   freecon(tcon);
-   return allowed;
-}
-
-static bool pid_contains_tid(pid_t pid, pid_t tid) {
-  char task_path[PATH_MAX];
-  if (snprintf(task_path, PATH_MAX, "/proc/%d/task/%d", pid, tid) >= PATH_MAX) {
-    ALOGE("debuggerd: task path overflow (pid = %d, tid = %d)\n", pid, tid);
-    exit(1);
-  }
-
-  return access(task_path, F_OK) == 0;
-}
-
-static int read_request(int fd, debugger_request_t* out_request) {
-  ucred cr;
-  socklen_t len = sizeof(cr);
-  int status = getsockopt(fd, SOL_SOCKET, SO_PEERCRED, &cr, &len);
-  if (status != 0) {
-    ALOGE("cannot get credentials");
-    return -1;
-  }
-
-  ALOGV("reading tid");
-  pollfd pollfds[1];
-  pollfds[0].fd = fd;
-  pollfds[0].events = POLLIN;
-  pollfds[0].revents = 0;
-  status = TEMP_FAILURE_RETRY(poll(pollfds, 1, 3000));
-  if (status != 1) {
-    ALOGE("timed out reading tid (from pid=%d uid=%d)\n", cr.pid, cr.uid);
-    return -1;
-  }
-
-  debugger_msg_t msg;
-  memset(&msg, 0, sizeof(msg));
-  status = TEMP_FAILURE_RETRY(read(fd, &msg, sizeof(msg)));
-  if (status < 0) {
-    ALOGE("read failure? %s (pid=%d uid=%d)\n", strerror(errno), cr.pid, cr.uid);
-    return -1;
-  }
-  if (status != sizeof(debugger_msg_t)) {
-    ALOGE("invalid crash request of size %d (from pid=%d uid=%d)\n", status, cr.pid, cr.uid);
-    return -1;
-  }
-
-  out_request->action = static_cast<debugger_action_t>(msg.action);
-  out_request->tid = msg.tid;
-  out_request->ignore_tid = msg.ignore_tid;
-  out_request->pid = cr.pid;
-  out_request->uid = cr.uid;
-  out_request->gid = cr.gid;
-  out_request->abort_msg_address = msg.abort_msg_address;
-
-  if (msg.action == DEBUGGER_ACTION_CRASH) {
-    // Ensure that the tid reported by the crashing process is valid.
-    // This check needs to happen again after ptracing the requested thread to prevent a race.
-    if (!pid_contains_tid(out_request->pid, out_request->tid)) {
-      ALOGE("tid %d does not exist in pid %d. ignoring debug request\n", out_request->tid,
-            out_request->pid);
-      return -1;
-    }
-  } else if (cr.uid == 0 || (cr.uid == AID_SYSTEM && msg.action == DEBUGGER_ACTION_DUMP_BACKTRACE)) {
-    // Only root or system can ask us to attach to any process and dump it explicitly.
-    // However, system is only allowed to collect backtraces but cannot dump tombstones.
-    status = get_process_info(out_request->tid, &out_request->pid,
-                              &out_request->uid, &out_request->gid);
-    if (status < 0) {
-      ALOGE("tid %d does not exist. ignoring explicit dump request\n", out_request->tid);
-      return -1;
-    }
-
-    if (!selinux_action_allowed(fd, out_request))
-      return -1;
-  } else {
-    // No one else is allowed to dump arbitrary processes.
-    return -1;
-  }
-  return 0;
-}
-
-static int activity_manager_connect() {
-  android::base::unique_fd amfd(socket(PF_UNIX, SOCK_STREAM, 0));
-  if (amfd.get() < -1) {
-    ALOGE("debuggerd: Unable to connect to activity manager (socket failed: %s)", strerror(errno));
-    return -1;
-  }
-
-  struct sockaddr_un address;
-  memset(&address, 0, sizeof(address));
-  address.sun_family = AF_UNIX;
-  // The path used here must match the value defined in NativeCrashListener.java.
-  strncpy(address.sun_path, "/data/system/ndebugsocket", sizeof(address.sun_path));
-  if (TEMP_FAILURE_RETRY(connect(amfd.get(), reinterpret_cast<struct sockaddr*>(&address),
-                                 sizeof(address))) == -1) {
-    ALOGE("debuggerd: Unable to connect to activity manager (connect failed: %s)", strerror(errno));
-    return -1;
-  }
-
-  struct timeval tv;
-  memset(&tv, 0, sizeof(tv));
-  tv.tv_sec = 1;  // tight leash
-  if (setsockopt(amfd.get(), SOL_SOCKET, SO_SNDTIMEO, &tv, sizeof(tv)) == -1) {
-    ALOGE("debuggerd: Unable to connect to activity manager (setsockopt SO_SNDTIMEO failed: %s)",
-          strerror(errno));
-    return -1;
-  }
-
-  tv.tv_sec = 3;  // 3 seconds on handshake read
-  if (setsockopt(amfd.get(), SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv)) == -1) {
-    ALOGE("debuggerd: Unable to connect to activity manager (setsockopt SO_RCVTIMEO failed: %s)",
-          strerror(errno));
-    return -1;
-  }
-
-  return amfd.release();
-}
-
-static void activity_manager_write(int pid, int signal, int amfd, const std::string& amfd_data) {
-  if (amfd == -1) {
-    return;
-  }
-
-  // Activity Manager protocol: binary 32-bit network-byte-order ints for the
-  // pid and signal number, followed by the raw text of the dump, culminating
-  // in a zero byte that marks end-of-data.
-  uint32_t datum = htonl(pid);
-  if (!android::base::WriteFully(amfd, &datum, 4)) {
-    ALOGE("AM pid write failed: %s\n", strerror(errno));
-    return;
-  }
-  datum = htonl(signal);
-  if (!android::base::WriteFully(amfd, &datum, 4)) {
-    ALOGE("AM signal write failed: %s\n", strerror(errno));
-    return;
-  }
-
-  if (!android::base::WriteFully(amfd, amfd_data.c_str(), amfd_data.size())) {
-    ALOGE("AM data write failed: %s\n", strerror(errno));
-    return;
-  }
-
-  // Send EOD to the Activity Manager, then wait for its ack to avoid racing
-  // ahead and killing the target out from under it.
-  uint8_t eodMarker = 0;
-  if (!android::base::WriteFully(amfd, &eodMarker, 1)) {
-    ALOGE("AM eod write failed: %s\n", strerror(errno));
-    return;
-  }
-  // 3 sec timeout reading the ack; we're fine if the read fails.
-  android::base::ReadFully(amfd, &eodMarker, 1);
-}
-
-static bool should_attach_gdb(const debugger_request_t& request) {
-  if (request.action == DEBUGGER_ACTION_CRASH) {
-    return property_get_bool("debug.debuggerd.wait_for_gdb", false);
-  }
-  return false;
-}
-
-#if defined(__LP64__)
-static bool is32bit(pid_t tid) {
-  char* exeline;
-  if (asprintf(&exeline, "/proc/%d/exe", tid) == -1) {
-    return false;
-  }
-  int fd = TEMP_FAILURE_RETRY(open(exeline, O_RDONLY | O_CLOEXEC));
-  int saved_errno = errno;
-  free(exeline);
-  if (fd == -1) {
-    ALOGW("Failed to open /proc/%d/exe %s", tid, strerror(saved_errno));
-    return false;
-  }
-
-  char ehdr[EI_NIDENT];
-  ssize_t bytes = TEMP_FAILURE_RETRY(read(fd, &ehdr, sizeof(ehdr)));
-  close(fd);
-  if (bytes != (ssize_t) sizeof(ehdr) || memcmp(ELFMAG, ehdr, SELFMAG) != 0) {
-    return false;
-  }
-  if (ehdr[EI_CLASS] == ELFCLASS32) {
-    return true;
-  }
-  return false;
-}
-
-static void redirect_to_32(int fd, debugger_request_t* request) {
-  debugger_msg_t msg;
-  memset(&msg, 0, sizeof(msg));
-  msg.tid = request->tid;
-  msg.action = request->action;
-
-  int sock_fd = socket_local_client(DEBUGGER32_SOCKET_NAME, ANDROID_SOCKET_NAMESPACE_ABSTRACT,
-                                    SOCK_STREAM | SOCK_CLOEXEC);
-  if (sock_fd < 0) {
-    ALOGE("Failed to connect to debuggerd32: %s", strerror(errno));
-    return;
-  }
-
-  if (TEMP_FAILURE_RETRY(write(sock_fd, &msg, sizeof(msg))) != (ssize_t) sizeof(msg)) {
-    ALOGE("Failed to write request to debuggerd32 socket: %s", strerror(errno));
-    close(sock_fd);
-    return;
-  }
-
-  char ack;
-  if (TEMP_FAILURE_RETRY(read(sock_fd, &ack, 1)) == -1) {
-    ALOGE("Failed to read ack from debuggerd32 socket: %s", strerror(errno));
-    close(sock_fd);
-    return;
-  }
-
-  char buffer[1024];
-  ssize_t bytes_read;
-  while ((bytes_read = TEMP_FAILURE_RETRY(read(sock_fd, buffer, sizeof(buffer)))) > 0) {
-    ssize_t bytes_to_send = bytes_read;
-    ssize_t bytes_written;
-    do {
-      bytes_written = TEMP_FAILURE_RETRY(write(fd, buffer + bytes_read - bytes_to_send,
-                                               bytes_to_send));
-      if (bytes_written == -1) {
-        if (errno == EAGAIN) {
-          // Retry the write.
-          continue;
-        }
-        ALOGE("Error while writing data to fd: %s", strerror(errno));
-        break;
+static std::thread spawn_redirect_thread(unique_fd fd) {
+  return std::thread([fd{ std::move(fd) }]() {
+    while (true) {
+      char buf[BUFSIZ];
+      ssize_t rc = TEMP_FAILURE_RETRY(read(fd.get(), buf, sizeof(buf)));
+      if (rc <= 0) {
+        return;
       }
-      bytes_to_send -= bytes_written;
-    } while (bytes_written != 0 && bytes_to_send > 0);
-    if (bytes_to_send != 0) {
-        ALOGE("Failed to write all data to fd: read %zd, sent %zd", bytes_read, bytes_to_send);
-        break;
-    }
-  }
-  close(sock_fd);
-}
-#endif
-
-// Attach to a thread, and verify that it's still a member of the given process
-static bool ptrace_attach_thread(pid_t pid, pid_t tid) {
-  if (ptrace(PTRACE_ATTACH, tid, 0, 0) != 0) {
-    return false;
-  }
-
-  // Make sure that the task we attached to is actually part of the pid we're dumping.
-  if (!pid_contains_tid(pid, tid)) {
-    if (ptrace(PTRACE_DETACH, tid, 0, 0) != 0) {
-      ALOGE("debuggerd: failed to detach from thread '%d'", tid);
-      exit(1);
-    }
-    return false;
-  }
-
-  return true;
-}
-
-static void ptrace_siblings(pid_t pid, pid_t main_tid, pid_t ignore_tid, std::set<pid_t>& tids) {
-  char task_path[PATH_MAX];
-
-  if (snprintf(task_path, PATH_MAX, "/proc/%d/task", pid) >= PATH_MAX) {
-    ALOGE("debuggerd: task path overflow (pid = %d)\n", pid);
-    abort();
-  }
-
-  std::unique_ptr<DIR, int (*)(DIR*)> d(opendir(task_path), closedir);
-
-  // Bail early if the task directory cannot be opened.
-  if (!d) {
-    ALOGE("debuggerd: failed to open /proc/%d/task: %s", pid, strerror(errno));
-    return;
-  }
-
-  struct dirent* de;
-  while ((de = readdir(d.get())) != NULL) {
-    // Ignore "." and "..".
-    if (!strcmp(de->d_name, ".") || !strcmp(de->d_name, "..")) {
-      continue;
-    }
-
-    char* end;
-    pid_t tid = strtoul(de->d_name, &end, 10);
-    if (*end) {
-      continue;
-    }
-
-    if (tid == main_tid || tid == ignore_tid) {
-      continue;
-    }
-
-    if (!ptrace_attach_thread(pid, tid)) {
-      ALOGE("debuggerd: ptrace attach to %d failed: %s", tid, strerror(errno));
-      continue;
-    }
 
-    tids.insert(tid);
-  }
-}
-
-static bool perform_dump(const debugger_request_t& request, int fd, int tombstone_fd,
-                         BacktraceMap* backtrace_map, const OpenFilesList& open_files,
-                         const std::set<pid_t>& siblings,
-                         int* crash_signal, std::string* amfd_data) {
-  if (TEMP_FAILURE_RETRY(write(fd, "\0", 1)) != 1) {
-    ALOGE("debuggerd: failed to respond to client: %s\n", strerror(errno));
-    return false;
-  }
-
-  while (true) {
-    // wait_for_signal waits for forever, but the watchdog process will kill us
-    // if it takes too long.
-    int signal = wait_for_signal(request.tid);
-    switch (signal) {
-      case -1:
-        ALOGE("debuggerd: timed out waiting for signal");
-        return false;
-
-      case SIGSTOP:
-        if (request.action == DEBUGGER_ACTION_DUMP_TOMBSTONE) {
-          ALOGV("debuggerd: stopped -- dumping to tombstone");
-          engrave_tombstone(tombstone_fd, backtrace_map, open_files,
-                            request.pid, request.tid, siblings,
-                            request.abort_msg_address, amfd_data);
-        } else if (request.action == DEBUGGER_ACTION_DUMP_BACKTRACE) {
-          ALOGV("debuggerd: stopped -- dumping to fd");
-          dump_backtrace(fd, backtrace_map, request.pid, request.tid, siblings, nullptr);
-        } else {
-          ALOGV("debuggerd: stopped -- continuing");
-          if (ptrace(PTRACE_CONT, request.tid, 0, 0) != 0) {
-            ALOGE("debuggerd: ptrace continue failed: %s", strerror(errno));
-            return false;
-          }
-          continue;  // loop again
-        }
-        break;
-
-      case SIGABRT:
-      case SIGBUS:
-      case SIGFPE:
-      case SIGILL:
-      case SIGSEGV:
-#ifdef SIGSTKFLT
-      case SIGSTKFLT:
-#endif
-      case SIGSYS:
-      case SIGTRAP:
-        ALOGV("stopped -- fatal signal\n");
-        *crash_signal = signal;
-        engrave_tombstone(tombstone_fd, backtrace_map, open_files,
-                          request.pid, request.tid, siblings,
-                          request.abort_msg_address, amfd_data);
-        break;
-
-      default:
-        ALOGE("debuggerd: process stopped due to unexpected signal %d\n", signal);
-        break;
-    }
-    break;
-  }
-
-  return true;
-}
-
-static bool drop_privileges() {
-  // AID_LOG: for reading the logs data associated with the crashing process.
-  // AID_READPROC: for reading /proc/<PID>/{comm,cmdline}.
-  gid_t groups[] = { AID_DEBUGGERD, AID_LOG, AID_READPROC };
-  if (setgroups(sizeof(groups)/sizeof(groups[0]), groups) != 0) {
-    ALOGE("debuggerd: failed to setgroups: %s", strerror(errno));
-    return false;
-  }
-
-  if (setresgid(AID_DEBUGGERD, AID_DEBUGGERD, AID_DEBUGGERD) != 0) {
-    ALOGE("debuggerd: failed to setresgid: %s", strerror(errno));
-    return false;
-  }
-
-  if (setresuid(AID_DEBUGGERD, AID_DEBUGGERD, AID_DEBUGGERD) != 0) {
-    ALOGE("debuggerd: failed to setresuid: %s", strerror(errno));
-    return false;
-  }
-
-  return true;
-}
-
-static void worker_process(int fd, debugger_request_t& request) {
-  // Open the tombstone file if we need it.
-  std::string tombstone_path;
-  int tombstone_fd = -1;
-  switch (request.action) {
-    case DEBUGGER_ACTION_DUMP_TOMBSTONE:
-    case DEBUGGER_ACTION_CRASH:
-      tombstone_fd = open_tombstone(&tombstone_path);
-      if (tombstone_fd == -1) {
-        ALOGE("debuggerd: failed to open tombstone file: %s\n", strerror(errno));
-        exit(1);
-      }
-      break;
-
-    case DEBUGGER_ACTION_DUMP_BACKTRACE:
-      break;
-
-    default:
-      ALOGE("debuggerd: unexpected request action: %d", request.action);
-      exit(1);
-  }
-
-  // At this point, the thread that made the request is blocked in
-  // a read() call.  If the thread has crashed, then this gives us
-  // time to PTRACE_ATTACH to it before it has a chance to really fault.
-  //
-  // The PTRACE_ATTACH sends a SIGSTOP to the target process, but it
-  // won't necessarily have stopped by the time ptrace() returns.  (We
-  // currently assume it does.)  We write to the file descriptor to
-  // ensure that it can run as soon as we call PTRACE_CONT below.
-  // See details in client/debuggerd_client.cpp, in function
-  // debugger_signal_handler().
-
-  // Attach to the target process.
-  if (!ptrace_attach_thread(request.pid, request.tid)) {
-    ALOGE("debuggerd: ptrace attach failed: %s", strerror(errno));
-    exit(1);
-  }
-
-  // DEBUGGER_ACTION_CRASH requests can come from arbitrary processes and the tid field in the
-  // request is sent from the other side. If an attacker can cause a process to be spawned with the
-  // pid of their process, they could trick debuggerd into dumping that process by exiting after
-  // sending the request. Validate the trusted request.uid/gid to defend against this.
-  if (request.action == DEBUGGER_ACTION_CRASH) {
-    pid_t pid;
-    uid_t uid;
-    gid_t gid;
-    if (get_process_info(request.tid, &pid, &uid, &gid) != 0) {
-      ALOGE("debuggerd: failed to get process info for tid '%d'", request.tid);
-      exit(1);
-    }
-
-    if (pid != request.pid || uid != request.uid || gid != request.gid) {
-      ALOGE(
-        "debuggerd: attached task %d does not match request: "
-        "expected pid=%d,uid=%d,gid=%d, actual pid=%d,uid=%d,gid=%d",
-        request.tid, request.pid, request.uid, request.gid, pid, uid, gid);
-      exit(1);
-    }
-  }
-
-  // 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);
-  if (attach_gdb) {
-    // Open all of the input devices we need to listen for VOLUMEDOWN before dropping privileges.
-    if (init_getevent() != 0) {
-      ALOGE("debuggerd: failed to initialize input device, not waiting for gdb");
-      attach_gdb = false;
-    }
-
-  }
-
-  std::set<pid_t> siblings;
-  if (!attach_gdb) {
-    ptrace_siblings(request.pid, request.tid, request.ignore_tid, siblings);
-  }
-
-  // Generate the backtrace map before dropping privileges.
-  std::unique_ptr<BacktraceMap> backtrace_map(BacktraceMap::Create(request.pid));
-
-  // Collect the list of open files before dropping privileges.
-  OpenFilesList open_files;
-  populate_open_files_list(request.pid, &open_files);
-
-  int amfd = -1;
-  std::unique_ptr<std::string> amfd_data;
-  if (request.action == DEBUGGER_ACTION_CRASH) {
-    // Connect to the activity manager before dropping privileges.
-    amfd = activity_manager_connect();
-    amfd_data.reset(new std::string);
-  }
-
-  bool succeeded = false;
-
-  // Now that we've done everything that requires privileges, we can drop them.
-  if (!drop_privileges()) {
-    ALOGE("debuggerd: failed to drop privileges, exiting");
-    _exit(1);
-  }
-
-  int crash_signal = SIGKILL;
-  succeeded = perform_dump(request, fd, tombstone_fd, backtrace_map.get(), open_files,
-                           siblings, &crash_signal, amfd_data.get());
-  if (succeeded) {
-    if (request.action == DEBUGGER_ACTION_DUMP_TOMBSTONE) {
-      if (!tombstone_path.empty()) {
-        android::base::WriteFully(fd, tombstone_path.c_str(), tombstone_path.length());
-      }
-    }
-  }
-
-  if (attach_gdb) {
-    // Tell the signal process to send SIGSTOP to the target.
-    if (!send_signal(request.pid, 0, SIGSTOP)) {
-      ALOGE("debuggerd: failed to stop process for gdb attach: %s", strerror(errno));
-      attach_gdb = false;
-    }
-  }
-
-  if (!attach_gdb) {
-    // Tell the Activity Manager about the crashing process. If we are
-    // waiting for gdb to attach, do not send this or Activity Manager
-    // might kill the process before anyone can attach.
-    activity_manager_write(request.pid, crash_signal, amfd, *amfd_data.get());
-  }
-
-  if (ptrace(PTRACE_DETACH, request.tid, 0, 0) != 0) {
-    ALOGE("debuggerd: ptrace detach from %d failed: %s", request.tid, strerror(errno));
-  }
-
-  for (pid_t sibling : siblings) {
-    ptrace(PTRACE_DETACH, sibling, 0, 0);
-  }
-
-  // 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(request.pid, request.tid, crash_signal)) {
-      ALOGE("debuggerd: failed to kill process %d: %s", request.pid, strerror(errno));
-    }
-  }
-
-  // Wait for gdb, if requested.
-  if (attach_gdb) {
-    wait_for_user_action(request);
-
-    // Now tell the activity manager about this process.
-    activity_manager_write(request.pid, crash_signal, amfd, *amfd_data.get());
-
-    // Tell the signal process to send SIGCONT to the target.
-    if (!send_signal(request.pid, 0, SIGCONT)) {
-      ALOGE("debuggerd: failed to resume process %d: %s", request.pid, strerror(errno));
-    }
-
-    uninit_getevent();
-  }
-
-  close(amfd);
-
-  exit(!succeeded);
-}
-
-static void monitor_worker_process(int child_pid, const debugger_request_t& request) {
-  struct timespec timeout = {.tv_sec = 10, .tv_nsec = 0 };
-  if (should_attach_gdb(request)) {
-    // If wait_for_gdb is enabled, set the timeout to something large.
-    timeout.tv_sec = INT_MAX;
-  }
-
-  sigset_t signal_set;
-  sigemptyset(&signal_set);
-  sigaddset(&signal_set, SIGCHLD);
-
-  bool kill_worker = false;
-  bool kill_target = false;
-  bool kill_self = false;
-
-  int status;
-  siginfo_t siginfo;
-  int signal = TEMP_FAILURE_RETRY(sigtimedwait(&signal_set, &siginfo, &timeout));
-  if (signal == SIGCHLD) {
-    pid_t rc = waitpid(-1, &status, WNOHANG | WUNTRACED);
-    if (rc != child_pid) {
-      ALOGE("debuggerd: waitpid returned unexpected pid (%d), committing murder-suicide", rc);
-
-      if (WIFEXITED(status)) {
-        ALOGW("debuggerd: pid %d exited with status %d", rc, WEXITSTATUS(status));
-      } else if (WIFSIGNALED(status)) {
-        ALOGW("debuggerd: pid %d received signal %d", rc, WTERMSIG(status));
-      } else if (WIFSTOPPED(status)) {
-        ALOGW("debuggerd: pid %d stopped by signal %d", rc, WSTOPSIG(status));
-      } else if (WIFCONTINUED(status)) {
-        ALOGW("debuggerd: pid %d continued", rc);
+      if (!android::base::WriteFully(STDOUT_FILENO, buf, rc)) {
+        return;
       }
-
-      kill_worker = true;
-      kill_target = true;
-      kill_self = true;
-    } else if (WIFSIGNALED(status)) {
-      ALOGE("debuggerd: worker process %d terminated due to signal %d", child_pid, WTERMSIG(status));
-      kill_worker = false;
-      kill_target = true;
-    } else if (WIFSTOPPED(status)) {
-      ALOGE("debuggerd: worker process %d stopped due to signal %d", child_pid, WSTOPSIG(status));
-      kill_worker = true;
-      kill_target = true;
-    }
-  } else {
-    ALOGE("debuggerd: worker process %d timed out", child_pid);
-    kill_worker = true;
-    kill_target = true;
-  }
-
-  if (kill_worker) {
-    // Something bad happened, kill the worker.
-    if (kill(child_pid, SIGKILL) != 0) {
-      ALOGE("debuggerd: failed to kill worker process %d: %s", child_pid, strerror(errno));
-    } else {
-      waitpid(child_pid, &status, 0);
     }
-  }
-
-  int exit_signal = SIGCONT;
-  if (kill_target && request.action == DEBUGGER_ACTION_CRASH) {
-    ALOGE("debuggerd: killing target %d", request.pid);
-    exit_signal = SIGKILL;
-  } else {
-    ALOGW("debuggerd: resuming target %d", request.pid);
-  }
-
-  if (kill(request.pid, exit_signal) != 0) {
-    ALOGE("debuggerd: failed to send signal %d to target: %s", exit_signal, strerror(errno));
-  }
-
-  if (kill_self) {
-    stop_signal_sender();
-    _exit(1);
-  }
+  });
 }
 
-static void handle_request(int fd) {
-  ALOGV("handle_request(%d)\n", fd);
+int main(int argc, char* argv[]) {
+  if (argc <= 1) usage(0);
+  if (argc > 3) usage(1);
+  if (argc == 3 && strcmp(argv[1], "-b") != 0) usage(1);
 
-  android::base::unique_fd closer(fd);
-  debugger_request_t request;
-  memset(&request, 0, sizeof(request));
-  int status = read_request(fd, &request);
-  if (status != 0) {
-    return;
+  pid_t pid;
+  if (!android::base::ParseInt(argv[argc - 1], &pid, 1, std::numeric_limits<pid_t>::max())) {
+    usage(1);
   }
 
-  ALOGW("debuggerd: handling request: pid=%d uid=%d gid=%d tid=%d\n", request.pid, request.uid,
-        request.gid, request.tid);
-
-#if defined(__LP64__)
-  // On 64 bit systems, requests to dump 32 bit and 64 bit tids come
-  // to the 64 bit debuggerd. If the process is a 32 bit executable,
-  // redirect the request to the 32 bit debuggerd.
-  if (is32bit(request.tid)) {
-    // Only dump backtrace and dump tombstone requests can be redirected.
-    if (request.action == DEBUGGER_ACTION_DUMP_BACKTRACE ||
-        request.action == DEBUGGER_ACTION_DUMP_TOMBSTONE) {
-      redirect_to_32(fd, &request);
-    } else {
-      ALOGE("debuggerd: Not allowed to redirect action %d to 32 bit debuggerd\n", request.action);
-    }
-    return;
+  unique_fd piperead, pipewrite;
+  if (!Pipe(&piperead, &pipewrite)) {
+    err(1, "failed to create pipe");
   }
-#endif
 
-  // Fork a child to handle the rest of the request.
-  pid_t fork_pid = fork();
-  if (fork_pid == -1) {
-    ALOGE("debuggerd: failed to fork: %s\n", strerror(errno));
-  } else if (fork_pid == 0) {
-    worker_process(fd, request);
-  } else {
-    monitor_worker_process(fork_pid, request);
+  std::thread redirect_thread = spawn_redirect_thread(std::move(piperead));
+  bool backtrace = argc == 3;
+  if (!debuggerd_trigger_dump(pid, std::move(pipewrite),
+                              backtrace ? kDebuggerdBacktrace : kDebuggerdBacktrace, 0)) {
+    redirect_thread.join();
+    errx(1, "failed to dump process %d", pid);
   }
-}
-
-static int do_server() {
-  // debuggerd crashes can't be reported to debuggerd.
-  // Reset all of the crash handlers.
-  signal(SIGABRT, SIG_DFL);
-  signal(SIGBUS, SIG_DFL);
-  signal(SIGFPE, SIG_DFL);
-  signal(SIGILL, SIG_DFL);
-  signal(SIGSEGV, SIG_DFL);
-#ifdef SIGSTKFLT
-  signal(SIGSTKFLT, SIG_DFL);
-#endif
-  signal(SIGTRAP, SIG_DFL);
-
-  // Ignore failed writes to closed sockets
-  signal(SIGPIPE, SIG_IGN);
-
-  // Block SIGCHLD so we can sigtimedwait for it.
-  sigset_t sigchld;
-  sigemptyset(&sigchld);
-  sigaddset(&sigchld, SIGCHLD);
-  sigprocmask(SIG_SETMASK, &sigchld, nullptr);
-
-  int s = socket_local_server(SOCKET_NAME, ANDROID_SOCKET_NAMESPACE_ABSTRACT,
-                              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 (;;) {
-    ALOGV("waiting for connection\n");
-    int fd = accept4(s, nullptr, nullptr, SOCK_CLOEXEC | SOCK_NONBLOCK);
-    if (fd == -1) {
-      ALOGE("accept failed: %s\n", strerror(errno));
-      continue;
-    }
-
-    handle_request(fd);
-  }
+  redirect_thread.join();
   return 0;
 }
-
-static int do_explicit_dump(pid_t tid, bool dump_backtrace) {
-  fprintf(stdout, "Sending request to dump task %d...\n", tid);
-  fflush(stdout);
-
-  // TODO: we could have better error reporting if debuggerd sent an error string back.
-  if (dump_backtrace) {
-    if (dump_backtrace_to_file(tid, fileno(stdout)) < 0) {
-      fputs("Error dumping backtrace (check logcat).\n", stderr);
-      return 1;
-    }
-  } else {
-    char tombstone_path[PATH_MAX];
-    if (dump_tombstone(tid, tombstone_path, sizeof(tombstone_path)) < 0) {
-      fputs("Error dumping tombstone (check logcat).\n", stderr);
-      return 1;
-    }
-    fprintf(stderr, "Tombstone written to: %s\n", tombstone_path);
-  }
-  return 0;
-}
-
-static int usage() {
-  fputs("usage: debuggerd [-b] [<tid>]\n"
-        "\n"
-        "Given a thread id, sends a request to debuggerd to dump that thread.\n"
-        "Otherwise, starts the debuggerd server.\n"
-        "\n"
-        "-b\tdump backtrace to console, otherwise generate tombstone\n", stderr);
-  return EXIT_FAILURE;
-}
-
-int main(int argc, char** argv) {
-  union selinux_callback cb;
-  if (argc == 1) {
-    cb.func_audit = audit_callback;
-    selinux_set_callback(SELINUX_CB_AUDIT, cb);
-    cb.func_log = selinux_log_callback;
-    selinux_set_callback(SELINUX_CB_LOG, cb);
-    return do_server();
-  }
-
-  bool dump_backtrace = false;
-  pid_t tid = 0;
-  for (int i = 1; i < argc; i++) {
-    if (!strcmp(argv[i], "-b")) {
-      dump_backtrace = true;
-    } else if (tid != 0 || (tid = atoi(argv[i])) == 0) {
-      // Only one tid is allowed. (And 0 isn't a valid tid.)
-      // atoi(3) returns 0 on failure to parse, so this catches anything else too.
-      return usage();
-    }
-  }
-  return (tid != 0) ? do_explicit_dump(tid, dump_backtrace) : usage();
-}