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platform_system_core/debuggerd/debuggerd.cpp

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/*
* Copyright 2006, 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 <stdio.h>
#include <errno.h>
#include <signal.h>
#include <pthread.h>
#include <stdarg.h>
#include <fcntl.h>
#include <sys/types.h>
#include <dirent.h>
#include <time.h>
#include <sys/ptrace.h>
#include <sys/wait.h>
#include <elf.h>
#include <sys/stat.h>
#include <sys/poll.h>
#include <selinux/android.h>
#include <log/logger.h>
#include <cutils/sockets.h>
#include <cutils/properties.h>
#include <cutils/debugger.h>
#include <linux/input.h>
#include <private/android_filesystem_config.h>
#include "backtrace.h"
#include "getevent.h"
#include "tombstone.h"
#include "utility.h"
struct debugger_request_t {
debugger_action_t action;
pid_t pid, tid;
uid_t uid, gid;
uintptr_t abort_msg_address;
int32_t original_si_code;
};
static void wait_for_user_action(const debugger_request_t &request) {
// Find out the name of the process that crashed.
char path[64];
snprintf(path, sizeof(path), "/proc/%d/exe", request.pid);
char exe[PATH_MAX];
int count;
if ((count = readlink(path, exe, sizeof(exe) - 1)) == -1) {
ALOGE("readlink('%s') failed: %s", path, strerror(errno));
strlcpy(exe, "unknown", sizeof(exe));
} else {
exe[count] = '\0';
}
// Explain how to attach the debugger.
ALOGI("********************************************************\n"
"* Process %d has been suspended while crashing.\n"
"* To attach gdbserver for a gdb connection on port 5039\n"
"* and start gdbclient:\n"
"*\n"
"* gdbclient %s :5039 %d\n"
"*\n"
"* Wait for gdb to start, then press the VOLUME DOWN key\n"
"* to let the process continue crashing.\n"
"********************************************************",
request.pid, exe, request.tid);
// Wait for VOLUME DOWN.
if (init_getevent() == 0) {
while (true) {
input_event e;
if (get_event(&e, -1) == 0) {
if (e.type == EV_KEY && e.code == KEY_VOLUMEDOWN && e.value == 0) {
break;
}
}
}
uninit_getevent();
}
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;
}
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 int selinux_enabled;
/*
* 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 bool selinux_action_allowed(int s, pid_t tid, debugger_action_t action)
{
char *scon = NULL, *tcon = NULL;
const char *tclass = "debuggerd";
const char *perm;
bool allowed = false;
if (selinux_enabled <= 0)
return true;
if (action <= 0 || action >= (sizeof(debuggerd_perms)/sizeof(debuggerd_perms[0]))) {
ALOGE("SELinux: No permission defined for debugger action %d", action);
return false;
}
perm = debuggerd_perms[action];
if (getpeercon(s, &scon) < 0) {
ALOGE("Cannot get peer context from socket\n");
goto out;
}
if (getpidcon(tid, &tcon) < 0) {
ALOGE("Cannot get context for tid %d\n", tid);
goto out;
}
allowed = (selinux_check_access(scon, tcon, tclass, perm, NULL) == 0);
out:
freecon(scon);
freecon(tcon);
return allowed;
}
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");
fcntl(fd, F_SETFL, O_NONBLOCK);
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 = msg.action;
out_request->tid = msg.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;
out_request->original_si_code = msg.original_si_code;
if (msg.action == DEBUGGER_ACTION_CRASH) {
// Ensure that the tid reported by the crashing process is valid.
char buf[64];
struct stat s;
snprintf(buf, sizeof buf, "/proc/%d/task/%d", out_request->pid, out_request->tid);
if (stat(buf, &s)) {
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->tid, out_request->action))
return -1;
} else {
// No one else is allowed to dump arbitrary processes.
return -1;
}
return 0;
}
static bool should_attach_gdb(debugger_request_t* request) {
if (request->action == DEBUGGER_ACTION_CRASH) {
char value[PROPERTY_VALUE_MAX];
property_get("debug.db.uid", value, "-1");
int debug_uid = atoi(value);
return debug_uid >= 0 && request->uid <= (uid_t)debug_uid;
}
return false;
}
static void handle_request(int fd) {
ALOGV("handle_request(%d)\n", fd);
debugger_request_t request;
memset(&request, 0, sizeof(request));
int status = read_request(fd, &request);
if (!status) {
ALOGV("BOOM: pid=%d uid=%d gid=%d tid=%d\n",
request.pid, request.uid, request.gid, request.tid);
// 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 bionic/libc/linker/debugger.c, in function
// debugger_signal_handler().
if (ptrace(PTRACE_ATTACH, request.tid, 0, 0)) {
ALOGE("ptrace attach failed: %s\n", strerror(errno));
} else {
bool detach_failed = false;
bool tid_unresponsive = false;
bool attach_gdb = should_attach_gdb(&request);
if (TEMP_FAILURE_RETRY(write(fd, "\0", 1)) != 1) {
ALOGE("failed responding to client: %s\n", strerror(errno));
} else {
char* tombstone_path = NULL;
if (request.action == DEBUGGER_ACTION_CRASH) {
close(fd);
fd = -1;
}
int total_sleep_time_usec = 0;
for (;;) {
int signal = wait_for_sigstop(request.tid, &total_sleep_time_usec, &detach_failed);
if (signal == -1) {
tid_unresponsive = true;
break;
}
switch (signal) {
case SIGSTOP:
if (request.action == DEBUGGER_ACTION_DUMP_TOMBSTONE) {
ALOGV("stopped -- dumping to tombstone\n");
tombstone_path = engrave_tombstone(request.pid, request.tid,
signal, request.original_si_code,
request.abort_msg_address, true,
&detach_failed, &total_sleep_time_usec);
} else if (request.action == DEBUGGER_ACTION_DUMP_BACKTRACE) {
ALOGV("stopped -- dumping to fd\n");
dump_backtrace(fd, -1, request.pid, request.tid, &detach_failed,
&total_sleep_time_usec);
} else {
ALOGV("stopped -- continuing\n");
status = ptrace(PTRACE_CONT, request.tid, 0, 0);
if (status) {
ALOGE("ptrace continue failed: %s\n", strerror(errno));
}
continue; // loop again
}
break;
case SIGABRT:
case SIGBUS:
case SIGFPE:
case SIGILL:
case SIGPIPE:
case SIGSEGV:
#ifdef SIGSTKFLT
case SIGSTKFLT:
#endif
case SIGTRAP:
ALOGV("stopped -- fatal signal\n");
// Send a SIGSTOP to the process to make all of
// the non-signaled threads stop moving. Without
// this we get a lot of "ptrace detach failed:
// No such process".
kill(request.pid, SIGSTOP);
// don't dump sibling threads when attaching to GDB because it
// makes the process less reliable, apparently...
tombstone_path = engrave_tombstone(request.pid, request.tid,
signal, request.original_si_code,
request.abort_msg_address, !attach_gdb,
&detach_failed, &total_sleep_time_usec);
break;
default:
ALOGE("process stopped due to unexpected signal %d\n", signal);
break;
}
break;
}
if (request.action == DEBUGGER_ACTION_DUMP_TOMBSTONE) {
if (tombstone_path) {
write(fd, tombstone_path, strlen(tombstone_path));
}
close(fd);
fd = -1;
}
free(tombstone_path);
}
if (!tid_unresponsive) {
ALOGV("detaching");
if (attach_gdb) {
// stop the process so we can debug
kill(request.pid, SIGSTOP);
}
if (ptrace(PTRACE_DETACH, request.tid, 0, 0)) {
ALOGE("ptrace detach from %d failed: %s", request.tid, strerror(errno));
detach_failed = true;
} else if (attach_gdb) {
// if debug.db.uid is set, its value indicates if we should wait
// for user action for the crashing process.
// in this case, we log a message and turn the debug LED on
// waiting for a gdb connection (for instance)
wait_for_user_action(request);
}
}
// resume stopped process (so it can crash in peace).
kill(request.pid, SIGCONT);
// If we didn't successfully detach, we're still the parent, and the
// actual parent won't receive a death notification via wait(2). At this point
// there's not much we can do about that.
if (detach_failed) {
ALOGE("debuggerd committing suicide to free the zombie!\n");
kill(getpid(), SIGKILL);
}
}
}
if (fd >= 0) {
close(fd);
}
}
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);
int logsocket = socket_local_client("logd", ANDROID_SOCKET_NAMESPACE_ABSTRACT, SOCK_DGRAM);
if (logsocket < 0) {
logsocket = -1;
} else {
fcntl(logsocket, F_SETFD, FD_CLOEXEC);
}
struct sigaction act;
act.sa_handler = SIG_DFL;
sigemptyset(&act.sa_mask);
sigaddset(&act.sa_mask,SIGCHLD);
act.sa_flags = SA_NOCLDWAIT;
sigaction(SIGCHLD, &act, 0);
int s = socket_local_server(DEBUGGER_SOCKET_NAME, ANDROID_SOCKET_NAMESPACE_ABSTRACT, SOCK_STREAM);
if (s < 0)
return 1;
fcntl(s, F_SETFD, FD_CLOEXEC);
ALOGI("debuggerd: " __DATE__ " " __TIME__ "\n");
for (;;) {
sockaddr addr;
socklen_t alen = sizeof(addr);
ALOGV("waiting for connection\n");
int fd = accept(s, &addr, &alen);
if (fd < 0) {
ALOGV("accept failed: %s\n", strerror(errno));
continue;
}
fcntl(fd, F_SETFD, FD_CLOEXEC);
handle_request(fd);
}
return 0;
}
static int do_explicit_dump(pid_t tid, bool dump_backtrace) {
fprintf(stdout, "Sending request to dump task %d.\n", tid);
if (dump_backtrace) {
fflush(stdout);
if (dump_backtrace_to_file(tid, fileno(stdout)) < 0) {
fputs("Error dumping backtrace.\n", stderr);
return 1;
}
} else {
char tombstone_path[PATH_MAX];
if (dump_tombstone(tid, tombstone_path, sizeof(tombstone_path)) < 0) {
fputs("Error dumping tombstone.\n", stderr);
return 1;
}
fprintf(stderr, "Tombstone written to: %s\n", tombstone_path);
}
return 0;
}
static void usage() {
fputs("Usage: -b [<tid>]\n"
" -b dump backtrace to console, otherwise dump full tombstone file\n"
"\n"
"If tid specified, sends a request to debuggerd to dump that task.\n"
"Otherwise, starts the debuggerd server.\n", stderr);
}
int main(int argc, char** argv) {
union selinux_callback cb;
if (argc == 1) {
selinux_enabled = is_selinux_enabled();
cb.func_log = selinux_log_callback;
selinux_set_callback(SELINUX_CB_LOG, cb);
return do_server();
}
bool dump_backtrace = false;
bool have_tid = false;
pid_t tid = 0;
for (int i = 1; i < argc; i++) {
if (!strcmp(argv[i], "-b")) {
dump_backtrace = true;
} else if (!have_tid) {
tid = atoi(argv[i]);
have_tid = true;
} else {
usage();
return 1;
}
}
if (!have_tid) {
usage();
return 1;
}
return do_explicit_dump(tid, dump_backtrace);
}
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