ACPR/android_system_core
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init: fix signal handling and LOG(FATAL) in child processes

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Child processes inherit the signal handlers and the 'Aborter' for
logging from their parent process.  In the case of init, fork()'ed
processes, will attempt to reboot the system if they receive a fatal
signal or if they call LOG(FATAL).  This is not the correct behavior;
these processes should terminate due to the provided signal like other
processes on the system.

This is particularly important as there are multiple LOG(FATAL) calls
in service.cpp for failures after fork() but before execv() when a
service is started.

Note, that pthread_atfork() is not a viable solution since clone() is
used in some cases instead of fork() and atfork handlers are not
called with clone().

Test: LOG(FATAL) from a child process of init and see that it
      terminates due to a signal correctly
Test: LOG(FATAL) from init proper and see that it reboots to the
      bootloader

Change-Id: I875ebd7a5f6b3f5e3e2c028af3306917c4409db3
This commit is contained in:
Tom Cherry 2017-08-25 15:10:48 -07:00
parent 2732a7e023
commit 1ca83249a1
2 changed files with 20 additions and 6 deletions
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12
init/init.cpp
View file

@ -354,7 +354,7 @@ static void set_usb_controller() {
}
}
static void install_reboot_signal_handlers() {
static void InstallRebootSignalHandlers() {
// Instead of panic'ing the kernel as is the default behavior when init crashes,
// we prefer to reboot to bootloader on development builds, as this will prevent
// boot looping bad configurations and allow both developers and test farms to easily
@ -362,7 +362,13 @@ static void install_reboot_signal_handlers() {
struct sigaction action;
memset(&action, 0, sizeof(action));
sigfillset(&action.sa_mask);
action.sa_handler = [](int) {
action.sa_handler = [](int signal) {
// These signal handlers are also caught for processes forked from init, however we do not
// want them to trigger reboot, so we directly call _exit() for children processes here.
if (getpid() != 1) {
_exit(signal);
}
// Calling DoReboot() or LOG(FATAL) is not a good option as this is a signal handler.
// RebootSystem uses syscall() which isn't actually async-signal-safe, but our only option
// and probably good enough given this is already an error case and only enabled for
@ -392,7 +398,7 @@ int main(int argc, char** argv) {
}
if (REBOOT_BOOTLOADER_ON_PANIC) {
install_reboot_signal_handlers();
InstallRebootSignalHandlers();
}
bool is_first_stage = (getenv("INIT_SECOND_STAGE") == nullptr);

14
init/log.cpp
View file

@ -19,6 +19,7 @@
#include <fcntl.h>
#include <linux/audit.h>
#include <string.h>
#include <unistd.h>
#include <android-base/logging.h>
#include <cutils/android_reboot.h>
@ -29,7 +30,14 @@
namespace android {
namespace init {
static void RebootAborter(const char* abort_message) {
static void InitAborter(const char* abort_message) {
// When init forks, it continues to use this aborter for LOG(FATAL), but we want children to
// simply abort instead of trying to reboot the system.
if (getpid() != 1) {
android::base::DefaultAborter(abort_message);
return;
}
// DoReboot() does a lot to try to shutdown the system cleanly. If something happens to call
// LOG(FATAL) in the shutdown path, we want to catch this and immediately use the syscall to
// reboot instead of recursing here.
@ -49,7 +57,7 @@ void InitKernelLogging(char* argv[]) {
int fd = open("/sys/fs/selinux/null", O_RDWR);
if (fd == -1) {
int saved_errno = errno;
android::base::InitLogging(argv, &android::base::KernelLogger, RebootAborter);
android::base::InitLogging(argv, &android::base::KernelLogger, InitAborter);
errno = saved_errno;
PLOG(FATAL) << "Couldn't open /sys/fs/selinux/null";
}
@ -58,7 +66,7 @@ void InitKernelLogging(char* argv[]) {
dup2(fd, 2);
if (fd > 2) close(fd);
android::base::InitLogging(argv, &android::base::KernelLogger, RebootAborter);
android::base::InitLogging(argv, &android::base::KernelLogger, InitAborter);
}
int selinux_klog_callback(int type, const char *fmt, ...) {