Merge "debuggerd_handler: properly crash when PR_GET_DUMPABLE is 0." (4e0648e7) · Commits · e / os / android_system_core

debuggerd/debuggerd_test.cpp

+30 −4

Original line number	Diff line number	Diff line
		@@ -17,6 +17,7 @@
		#include <err.h>
		#include <fcntl.h>
		#include <unistd.h>
		#include <sys/prctl.h>
		#include <sys/types.h>

		#include <chrono>
		@@ -90,6 +91,7 @@ class CrasherTest : public ::testing::Test {
		// Returns -1 if we fail to read a response from tombstoned, otherwise the received return code.
		void FinishIntercept(int* result);

		void StartProcess(std::function<void()> function);
		void StartCrasher(const std::string& crash_type);
		void FinishCrasher();
		void AssertDeath(int signo);
		@@ -166,9 +168,8 @@ void CrasherTest::FinishIntercept(int* result) {
		}
		}

		void CrasherTest::StartCrasher(const std::string& crash_type) {
		std::string type = "wait-" + crash_type;

		void CrasherTest::StartProcess(std::function<void()> function) {
		unique_fd read_pipe;
		unique_fd crasher_read_pipe;
		if (!Pipe(&crasher_read_pipe, &crasher_pipe)) {
		FAIL() << "failed to create pipe: " << strerror(errno);
		@@ -182,9 +183,17 @@ void CrasherTest::StartCrasher(const std::string& crash_type) {
		dup2(crasher_read_pipe.get(), STDIN_FILENO);
		dup2(devnull.get(), STDOUT_FILENO);
		dup2(devnull.get(), STDERR_FILENO);
		function();
		_exit(0);
		}
		}

		void CrasherTest::StartCrasher(const std::string& crash_type) {
		std::string type = "wait-" + crash_type;
		StartProcess([type]() {
		execl(CRASHER_PATH, CRASHER_PATH, type.c_str(), nullptr);
		err(1, "exec failed");
		}
		});
		}

		void CrasherTest::FinishCrasher() {
		@@ -379,3 +388,20 @@ TEST_F(CrasherTest, backtrace) {
		ConsumeFd(std::move(output_fd), &result);
		ASSERT_MATCH(result, R"(#00 pc [0-9a-f]+\s+ /system/lib)" ARCH_SUFFIX R"(/libc.so \(tgkill)");
		}

		TEST_F(CrasherTest, PR_SET_DUMPABLE_0_crash) {
		StartProcess([]() {
		prctl(PR_SET_DUMPABLE, 0);
		volatile char* null = static_cast<char*>(nullptr);
		*null = '\0';
		});
		AssertDeath(SIGSEGV);
		}

		TEST_F(CrasherTest, PR_SET_DUMPABLE_0_raise) {
		StartProcess([]() {
		prctl(PR_SET_DUMPABLE, 0);
		raise(SIGUSR1);
		});
		AssertDeath(SIGUSR1);
		}

debuggerd/handler/debuggerd_handler.cpp

+55 −43

Original line number	Diff line number	Diff line
		@@ -63,6 +63,9 @@

		static debuggerd_callbacks_t g_callbacks;

		// Mutex to ensure only one crashing thread dumps itself.
		static pthread_mutex_t crash_mutex = PTHREAD_MUTEX_INITIALIZER;

		// Don't use __libc_fatal because it exits via abort, which might put us back into a signal handler.
		#define fatal(...) \
		do { \
		@@ -153,7 +156,7 @@ static bool have_siginfo(int signum) {
		}

		struct debugger_thread_info {
		bool crash_dump_started = false;
		bool crash_dump_started;
		pid_t crashing_tid;
		pid_t pseudothread_tid;
		int signal_number;
		@@ -233,12 +236,37 @@ static int debuggerd_dispatch_pseudothread(void* arg) {
		return 0;
		}

		static void resend_signal(siginfo_t* info) {
		// Signals can either be fatal or nonfatal.
		// For fatal signals, crash_dump will send us the signal we crashed with
		// before resuming us, so that processes using waitpid on us will see that we
		// exited with the correct exit status (e.g. so that sh will report
		// "Segmentation fault" instead of "Killed"). For this to work, we need
		// to deregister our signal handler for that signal before continuing.
		if (info->si_signo != DEBUGGER_SIGNAL) {
		signal(info->si_signo, SIG_DFL);
		}

		// We need to return from our signal handler so that crash_dump can see the
		// signal via ptrace and dump the thread that crashed. However, returning
		// does not guarantee that the signal will be thrown again, even for SIGSEGV
		// and friends, since the signal could have been sent manually. We blocked
		// all signals when registering the handler, so resending the signal (using
		// rt_tgsigqueueinfo(2) to preserve SA_SIGINFO) will cause it to be delivered
		// when our signal handler returns.
		int rc = syscall(SYS_rt_tgsigqueueinfo, getpid(), gettid(), info->si_signo, info);
		if (rc != 0) {
		fatal("failed to resend signal during crash: %s", strerror(errno));
		}

		if (info->si_signo == DEBUGGER_SIGNAL) {
		pthread_mutex_unlock(&crash_mutex);
		}
		}

		// Handler that does crash dumping by forking and doing the processing in the child.
		// Do this by ptracing the relevant thread, and then execing debuggerd to do the actual dump.
		static void debuggerd_signal_handler(int signal_number, siginfo_t* info, void*) {
		// 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_lock(&crash_mutex);
		if (ret != 0) {
		__libc_format_log(ANDROID_LOG_INFO, "libc", "pthread_mutex_lock failed: %s", strerror(ret));
		@@ -251,14 +279,28 @@ static void debuggerd_signal_handler(int signal_number, siginfo_t* info, void*)
		info = nullptr;
		}

		struct siginfo si = {};
		if (!info) {
		memset(&si, 0, sizeof(si));
		si.si_signo = signal_number;
		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.
		}

		log_signal_summary(signal_number, info);
		if (prctl(PR_GET_DUMPABLE, 0, 0, 0, 0) == 0) {
		// process has disabled core dumps and PTRACE_ATTACH, and does not want to be dumped.
		// Honor that intention by not connecting to debuggerd and asking it to dump our internal state.
		// The process has disabled core dumps and PTRACE_ATTACH, and does not want to be dumped.
		__libc_format_log(ANDROID_LOG_INFO, "libc",
		"Suppressing debuggerd output because prctl(PR_GET_DUMPABLE)==0");

		pthread_mutex_unlock(&crash_mutex);
		resend_signal(info);
		return;
		}

		@@ -266,8 +308,13 @@ static void debuggerd_signal_handler(int signal_number, siginfo_t* info, void*)
		if (g_callbacks.get_abort_message) {
		abort_message = g_callbacks.get_abort_message();
		}
		// Populate si_value with the abort message address, if found.
		if (abort_message) {
		info->si_value.sival_ptr = abort_message;
		}

		debugger_thread_info thread_info = {
		.crash_dump_started = false,
		.pseudothread_tid = -1,
		.crashing_tid = gettid(),
		.signal_number = signal_number,
		@@ -299,42 +346,7 @@ static void debuggerd_signal_handler(int signal_number, siginfo_t* info, void*)
		signal(signal_number, SIG_DFL);
		}

		// 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.
		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.
		}

		// Populate si_value with the abort message address, if found.
		if (abort_message) {
		info->si_value.sival_ptr = abort_message;
		}

		// Only resend the signal if we know that either crash_dump has ptraced us or
		// the signal was fatal.
		if (thread_info.crash_dump_started \|\| signal_number != DEBUGGER_SIGNAL) {
		int rc = syscall(SYS_rt_tgsigqueueinfo, getpid(), gettid(), signal_number, info);
		if (rc != 0) {
		fatal("failed to resend signal during crash: %s", strerror(errno));
		}
		}

		if (signal_number == DEBUGGER_SIGNAL) {
		pthread_mutex_unlock(&crash_mutex);
		}
		resend_signal(info);
		}

		void debuggerd_init(debuggerd_callbacks_t* callbacks) {