blob: c67d747fc54e14e80475649d945e90bbad5dbb4b [file] [log] [blame]
/*
* Copyright (C) 2008 The Android Open Source Project
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include "debuggerd/client.h"
#include <errno.h>
#include <inttypes.h>
#include <pthread.h>
#include <sched.h>
#include <signal.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/prctl.h>
#include <sys/socket.h>
#include <sys/syscall.h>
#include <sys/un.h>
#include <sys/wait.h>
#include <unistd.h>
#include "private/libc_logging.h"
#if defined(TARGET_IS_64_BIT) && !defined(__LP64__)
#define SOCKET_NAME "android:debuggerd32"
#else
#define SOCKET_NAME "android:debuggerd"
#endif
// see man(2) prctl, specifically the section about PR_GET_NAME
#define MAX_TASK_NAME_LEN (16)
static debuggerd_callbacks_t g_callbacks;
// Don't use __libc_fatal because it exits via abort, which might put us back into a signal handler.
#define fatal(...) \
do { \
__libc_format_log(ANDROID_LOG_FATAL, "libc", __VA_ARGS__); \
_exit(1); \
} while (0)
static int socket_abstract_client(const char* name, int type) {
sockaddr_un addr;
// Test with length +1 for the *initial* '\0'.
size_t namelen = strlen(name);
if ((namelen + 1) > sizeof(addr.sun_path)) {
errno = EINVAL;
return -1;
}
// This is used for abstract socket namespace, we need
// an initial '\0' at the start of the Unix socket path.
//
// Note: The path in this case is *not* supposed to be
// '\0'-terminated. ("man 7 unix" for the gory details.)
memset(&addr, 0, sizeof(addr));
addr.sun_family = AF_LOCAL;
addr.sun_path[0] = 0;
memcpy(addr.sun_path + 1, name, namelen);
socklen_t alen = namelen + offsetof(sockaddr_un, sun_path) + 1;
int s = socket(AF_LOCAL, type, 0);
if (s == -1) {
return -1;
}
int rc = TEMP_FAILURE_RETRY(connect(s, reinterpret_cast<sockaddr*>(&addr), alen));
if (rc == -1) {
close(s);
return -1;
}
return s;
}
/*
* Writes a summary of the signal to the log file. We do this so that, if
* for some reason we're not able to contact debuggerd, there is still some
* indication of the failure in the log.
*
* We could be here as a result of native heap corruption, or while a
* mutex is being held, so we don't want to use any libc functions that
* could allocate memory or hold a lock.
*/
static void log_signal_summary(int signum, const siginfo_t* info) {
const char* signal_name = "???";
bool has_address = false;
switch (signum) {
case SIGABRT:
signal_name = "SIGABRT";
break;
case SIGBUS:
signal_name = "SIGBUS";
has_address = true;
break;
case SIGFPE:
signal_name = "SIGFPE";
has_address = true;
break;
case SIGILL:
signal_name = "SIGILL";
has_address = true;
break;
case SIGSEGV:
signal_name = "SIGSEGV";
has_address = true;
break;
#if defined(SIGSTKFLT)
case SIGSTKFLT:
signal_name = "SIGSTKFLT";
break;
#endif
case SIGSYS:
signal_name = "SIGSYS";
break;
case SIGTRAP:
signal_name = "SIGTRAP";
break;
}
char thread_name[MAX_TASK_NAME_LEN + 1]; // one more for termination
if (prctl(PR_GET_NAME, reinterpret_cast<unsigned long>(thread_name), 0, 0, 0) != 0) {
strcpy(thread_name, "<name unknown>");
} else {
// short names are null terminated by prctl, but the man page
// implies that 16 byte names are not.
thread_name[MAX_TASK_NAME_LEN] = 0;
}
// "info" will be null if the siginfo_t information was not available.
// Many signals don't have an address or a code.
char code_desc[32]; // ", code -6"
char addr_desc[32]; // ", fault addr 0x1234"
addr_desc[0] = code_desc[0] = 0;
if (info != nullptr) {
// For a rethrown signal, this si_code will be right and the one debuggerd shows will
// always be SI_TKILL.
__libc_format_buffer(code_desc, sizeof(code_desc), ", code %d", info->si_code);
if (has_address) {
__libc_format_buffer(addr_desc, sizeof(addr_desc), ", fault addr %p", info->si_addr);
}
}
__libc_format_log(ANDROID_LOG_FATAL, "libc", "Fatal signal %d (%s)%s%s in tid %d (%s)", signum,
signal_name, code_desc, addr_desc, gettid(), thread_name);
}
/*
* Returns true if the handler for signal "signum" has SA_SIGINFO set.
*/
static bool have_siginfo(int signum) {
struct sigaction old_action, new_action;
memset(&new_action, 0, sizeof(new_action));
new_action.sa_handler = SIG_DFL;
new_action.sa_flags = SA_RESTART;
sigemptyset(&new_action.sa_mask);
if (sigaction(signum, &new_action, &old_action) < 0) {
__libc_format_log(ANDROID_LOG_WARN, "libc", "Failed testing for SA_SIGINFO: %s",
strerror(errno));
return false;
}
bool result = (old_action.sa_flags & SA_SIGINFO) != 0;
if (sigaction(signum, &old_action, nullptr) == -1) {
__libc_format_log(ANDROID_LOG_WARN, "libc", "Restore failed in test for SA_SIGINFO: %s",
strerror(errno));
}
return result;
}
static void send_debuggerd_packet(pid_t crashing_tid, pid_t pseudothread_tid) {
// Mutex to prevent multiple crashing threads from trying to talk
// to debuggerd at the same time.
static pthread_mutex_t crash_mutex = PTHREAD_MUTEX_INITIALIZER;
int ret = pthread_mutex_trylock(&crash_mutex);
if (ret != 0) {
if (ret == EBUSY) {
__libc_format_log(ANDROID_LOG_INFO, "libc",
"Another thread contacted debuggerd first; not contacting debuggerd.");
// This will never complete since the lock is never released.
pthread_mutex_lock(&crash_mutex);
} else {
__libc_format_log(ANDROID_LOG_INFO, "libc", "pthread_mutex_trylock failed: %s", strerror(ret));
}
return;
}
int s = socket_abstract_client(SOCKET_NAME, SOCK_STREAM | SOCK_CLOEXEC);
if (s == -1) {
__libc_format_log(ANDROID_LOG_FATAL, "libc", "Unable to open connection to debuggerd: %s",
strerror(errno));
return;
}
// debuggerd knows our pid from the credentials on the
// local socket but we need to tell it the tid of the crashing thread.
// debuggerd will be paranoid and verify that we sent a tid
// that's actually in our process.
debugger_msg_t msg;
msg.action = DEBUGGER_ACTION_CRASH;
msg.tid = crashing_tid;
msg.ignore_tid = pseudothread_tid;
msg.abort_msg_address = 0;
if (g_callbacks.get_abort_message) {
msg.abort_msg_address = reinterpret_cast<uintptr_t>(g_callbacks.get_abort_message());
}
ret = TEMP_FAILURE_RETRY(write(s, &msg, sizeof(msg)));
if (ret == sizeof(msg)) {
char debuggerd_ack;
ret = TEMP_FAILURE_RETRY(read(s, &debuggerd_ack, 1));
if (g_callbacks.post_dump) {
g_callbacks.post_dump();
}
} else {
// read or write failed -- broken connection?
__libc_format_log(ANDROID_LOG_FATAL, "libc", "Failed while talking to debuggerd: %s",
strerror(errno));
}
close(s);
}
struct debugger_thread_info {
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
pid_t crashing_tid;
pid_t pseudothread_tid;
int signal_number;
siginfo_t* info;
};
// Logging and contacting debuggerd requires free file descriptors, which we might not have.
// Work around this by spawning a "thread" that shares its parent's address space, but not its file
// descriptor table, so that we can close random file descriptors without affecting the original
// process. Note that this doesn't go through pthread_create, so TLS is shared with the spawning
// process.
static void* pseudothread_stack;
static int debuggerd_dispatch_pseudothread(void* arg) {
debugger_thread_info* thread_info = static_cast<debugger_thread_info*>(arg);
for (int i = 3; i < 1024; ++i) {
close(i);
}
log_signal_summary(thread_info->signal_number, thread_info->info);
send_debuggerd_packet(thread_info->crashing_tid, thread_info->pseudothread_tid);
pthread_mutex_unlock(&thread_info->mutex);
return 0;
}
/*
* Catches fatal signals so we can ask debuggerd to ptrace us before
* we crash.
*/
static void debuggerd_signal_handler(int signal_number, siginfo_t* info, void*) {
// It's possible somebody cleared the SA_SIGINFO flag, which would mean
// our "info" arg holds an undefined value.
if (!have_siginfo(signal_number)) {
info = nullptr;
}
debugger_thread_info thread_info = {
.crashing_tid = gettid(),
.signal_number = signal_number,
.info = info
};
pthread_mutex_lock(&thread_info.mutex);
pid_t child_pid = clone(debuggerd_dispatch_pseudothread, pseudothread_stack,
CLONE_THREAD | CLONE_SIGHAND | CLONE_VM | CLONE_CHILD_SETTID,
&thread_info, nullptr, nullptr, &thread_info.pseudothread_tid);
if (child_pid == -1) {
fatal("failed to spawn debuggerd dispatch thread: %s", strerror(errno));
}
// Wait for the child to finish and unlock the mutex.
// This relies on bionic behavior that isn't guaranteed by the standard.
pthread_mutex_lock(&thread_info.mutex);
// We need to return from the signal handler so that debuggerd can dump the
// thread that crashed, but returning here does not guarantee that the signal
// will be thrown again, even for SIGSEGV and friends, since the signal could
// have been sent manually. Resend the signal with rt_tgsigqueueinfo(2) to
// preserve the SA_SIGINFO contents.
signal(signal_number, SIG_DFL);
struct siginfo si;
if (!info) {
memset(&si, 0, sizeof(si));
si.si_code = SI_USER;
si.si_pid = getpid();
si.si_uid = getuid();
info = &si;
} else if (info->si_code >= 0 || info->si_code == SI_TKILL) {
// rt_tgsigqueueinfo(2)'s documentation appears to be incorrect on kernels
// that contain commit 66dd34a (3.9+). The manpage claims to only allow
// negative si_code values that are not SI_TKILL, but 66dd34a changed the
// check to allow all si_code values in calls coming from inside the house.
}
int rc = syscall(SYS_rt_tgsigqueueinfo, getpid(), gettid(), signal_number, info);
if (rc != 0) {
fatal("failed to resend signal during crash: %s", strerror(errno));
}
}
void debuggerd_init(debuggerd_callbacks_t* callbacks) {
if (callbacks) {
g_callbacks = *callbacks;
}
void* thread_stack_allocation =
mmap(nullptr, PAGE_SIZE * 3, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
if (thread_stack_allocation == MAP_FAILED) {
fatal("failed to allocate debuggerd thread stack");
}
char* stack = static_cast<char*>(thread_stack_allocation) + PAGE_SIZE;
if (mprotect(stack, PAGE_SIZE, PROT_READ | PROT_WRITE) != 0) {
fatal("failed to mprotect debuggerd thread stack");
}
// Stack grows negatively, set it to the last byte in the page...
stack = (stack + PAGE_SIZE - 1);
// and align it.
stack -= 15;
pseudothread_stack = stack;
struct sigaction action;
memset(&action, 0, sizeof(action));
sigemptyset(&action.sa_mask);
action.sa_sigaction = debuggerd_signal_handler;
action.sa_flags = SA_RESTART | SA_SIGINFO;
// Use the alternate signal stack if available so we can catch stack overflows.
action.sa_flags |= SA_ONSTACK;
sigaction(SIGABRT, &action, nullptr);
sigaction(SIGBUS, &action, nullptr);
sigaction(SIGFPE, &action, nullptr);
sigaction(SIGILL, &action, nullptr);
sigaction(SIGSEGV, &action, nullptr);
#if defined(SIGSTKFLT)
sigaction(SIGSTKFLT, &action, nullptr);
#endif
sigaction(SIGTRAP, &action, nullptr);
}