init: dump stack when aborting

Dump init stacks when aborting either due to LOG(FATAL) or in
userdebug/eng builds due to signals, including signals from
sanitizers.

Doesn't work for static first stage init yet, b/133450393 tracks
that.

Also, ensure that LOG(FATAL) in child processes calls abort() in all
stages of init, not just 2nd stage init.

Bug: 131747478
Test: abort init in various ways and see stacks
Test: hang or crash in backtrace handler and see child reboot
Change-Id: Ib53b5d3e7e814244203f875de016ada9900dfce8

init/Android.bp

@@ -68,6 +68,7 @@ cc_defaults {
         "libpropertyinfoparser",
     ],
     shared_libs: [
+        "libbacktrace",
         "libbase",
         "libbinder",
         "libbootloader_message",

init/Android.mk

@@ -105,6 +105,10 @@ LOCAL_STATIC_LIBRARIES := \
     libcap \
     libgsi \
     libcom.android.sysprop.apex \
+    liblzma \
+    libdexfile_support \
+    libunwindstack \
+    libbacktrace \
 
 LOCAL_SANITIZE := signed-integer-overflow
 # First stage init is weird: it may start without stdout/stderr, and no /proc.

init/first_stage_init.cpp

@@ -33,7 +33,6 @@
 #include <android-base/chrono_utils.h>
 #include <android-base/file.h>
 #include <android-base/logging.h>
-#include <cutils/android_reboot.h>
 #include <private/android_filesystem_config.h>
 
 #include "debug_ramdisk.h"
@@ -168,13 +167,10 @@ int FirstStageMain(int argc, char** argv) {
                     "mode=0755,uid=0,gid=0"));
 #undef CHECKCALL
 
+    SetStdioToDevNull(argv);
     // Now that tmpfs is mounted on /dev and we have /dev/kmsg, we can actually
     // talk to the outside world...
-    // We need to set up stdin/stdout/stderr for child processes forked from first
-    // stage init as part of the mount process.  This closes /dev/console if the
-    // kernel had previously opened it.
-    auto reboot_bootloader = [](const char*) { RebootSystem(ANDROID_RB_RESTART2, "bootloader"); };
-    InitKernelLogging(argv, reboot_bootloader);
+    InitKernelLogging(argv);
 
     if (!errors.empty()) {
         for (const auto& [error_string, error_errno] : errors) {

init/host_init_stubs.h

@@ -44,6 +44,11 @@ extern uint32_t (*property_set)(const std::string& name, const std::string& valu
 uint32_t HandlePropertySet(const std::string& name, const std::string& value,
                            const std::string& source_context, const ucred& cr, std::string* error);
 
+// reboot_utils.h
+inline void __attribute__((noreturn)) InitFatalReboot() {
+    abort();
+}
+
 // selinux.h
 int SelinuxGetVendorAndroidVersion();
 void SelabelInitialize();

init/init.cpp

@@ -39,7 +39,6 @@
 #include <android-base/properties.h>
 #include <android-base/stringprintf.h>
 #include <android-base/strings.h>
-#include <cutils/android_reboot.h>
 #include <fs_avb/fs_avb.h>
 #include <fs_mgr_vendor_overlay.h>
 #include <keyutils.h>
@@ -605,17 +604,6 @@ void HandleKeychord(const std::vector<int>& keycodes) {
     }
 }
 
-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;
-    }
-
-    RebootSystem(ANDROID_RB_RESTART2, "bootloader");
-}
-
 static void GlobalSeccomp() {
     import_kernel_cmdline(false, [](const std::string& key, const std::string& value,
                                     bool in_qemu) {
@@ -663,8 +651,8 @@ int SecondStageMain(int argc, char** argv) {
 
     boot_clock::time_point start_time = boot_clock::now();
 
-    // We need to set up stdin/stdout/stderr again now that we're running in init's context.
-    InitKernelLogging(argv, InitAborter);
+    SetStdioToDevNull(argv);
+    InitKernelLogging(argv);
     LOG(INFO) << "init second stage started!";
 
     // Set init and its forked children's oom_adj.

init/reboot_utils.cpp

@@ -19,8 +19,13 @@
 #include <sys/syscall.h>
 #include <unistd.h>
 
-#include <android-base/logging.h>
-#include <cutils/android_reboot.h>
+#include <string>
+
+#include "android-base/file.h"
+#include "android-base/logging.h"
+#include "android-base/strings.h"
+#include "backtrace/Backtrace.h"
+#include "cutils/android_reboot.h"
 
 #include "capabilities.h"
 
@@ -75,6 +80,32 @@ void __attribute__((noreturn)) RebootSystem(unsigned int cmd, const std::string&
     abort();
 }
 
+void __attribute__((noreturn)) InitFatalReboot() {
+    auto pid = fork();
+
+    if (pid == -1) {
+        // Couldn't fork, don't even try to backtrace, just reboot.
+        RebootSystem(ANDROID_RB_RESTART2, "bootloader");
+    } else if (pid == 0) {
+        // Fork a child for safety, since we always want to shut down if something goes wrong, but
+        // its worth trying to get the backtrace, even in the signal handler, since typically it
+        // does work despite not being async-signal-safe.
+        sleep(5);
+        RebootSystem(ANDROID_RB_RESTART2, "bootloader");
+    }
+
+    // In the parent, let's try to get a backtrace then shutdown.
+    std::unique_ptr<Backtrace> backtrace(
+            Backtrace::Create(BACKTRACE_CURRENT_PROCESS, BACKTRACE_CURRENT_THREAD));
+    if (!backtrace->Unwind(0)) {
+        LOG(ERROR) << __FUNCTION__ << ": Failed to unwind callstack.";
+    }
+    for (size_t i = 0; i < backtrace->NumFrames(); i++) {
+        LOG(ERROR) << backtrace->FormatFrameData(i);
+    }
+    RebootSystem(ANDROID_RB_RESTART2, "bootloader");
+}
+
 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
@@ -94,7 +125,7 @@ void InstallRebootSignalHandlers() {
         // 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
         // development builds.
-        RebootSystem(ANDROID_RB_RESTART2, "bootloader");
+        InitFatalReboot();
     };
     action.sa_flags = SA_RESTART;
     sigaction(SIGABRT, &action, nullptr);

init/reboot_utils.h

@@ -26,6 +26,7 @@ namespace init {
 bool IsRebootCapable();
 // This is a wrapper around the actual reboot calls.
 void __attribute__((noreturn)) RebootSystem(unsigned int cmd, const std::string& reboot_target);
+void __attribute__((noreturn)) InitFatalReboot();
 void InstallRebootSignalHandlers();
 
 }  // namespace init

init/selinux.cpp

@@ -60,7 +60,6 @@
 #include <android-base/logging.h>
 #include <android-base/parseint.h>
 #include <android-base/unique_fd.h>
-#include <cutils/android_reboot.h>
 #include <fs_avb/fs_avb.h>
 #include <selinux/android.h>
 
@@ -522,9 +521,7 @@ int SelinuxGetVendorAndroidVersion() {
 
 // This function initializes SELinux then execs init to run in the init SELinux context.
 int SetupSelinux(char** argv) {
-    android::base::InitLogging(argv, &android::base::KernelLogger, [](const char*) {
-        RebootSystem(ANDROID_RB_RESTART2, "bootloader");
-    });
+    InitKernelLogging(argv);
 
     if (REBOOT_BOOTLOADER_ON_PANIC) {
         InstallRebootSignalHandlers();

init/util.cpp

@@ -40,6 +40,7 @@
 #include <selinux/android.h>
 
 #if defined(__ANDROID__)
+#include "reboot_utils.h"
 #include "selinux.h"
 #else
 #include "host_init_stubs.h"
@@ -425,20 +426,49 @@ bool IsLegalPropertyName(const std::string& name) {
     return true;
 }
 
-void InitKernelLogging(char** argv, std::function<void(const char*)> abort_function) {
+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;
+    }
+
+    InitFatalReboot();
+}
+
+// The kernel opens /dev/console and uses that fd for stdin/stdout/stderr if there is a serial
+// console enabled and no initramfs, otherwise it does not provide any fds for stdin/stdout/stderr.
+// SetStdioToDevNull() is used to close these existing fds if they exist and replace them with
+// /dev/null regardless.
+//
+// In the case that these fds are provided by the kernel, the exec of second stage init causes an
+// SELinux denial as it does not have access to /dev/console.  In the case that they are not
+// provided, exec of any further process is potentially dangerous as the first fd's opened by that
+// process will take the stdin/stdout/stderr fileno's, which can cause issues if printf(), etc is
+// then used by that process.
+//
+// Lastly, simply calling SetStdioToDevNull() in first stage init is not enough, since first
+// stage init still runs in kernel context, future child processes will not have permissions to
+// access any fds that it opens, including the one opened below for /dev/null.  Therefore,
+// SetStdioToDevNull() must be called again in second stage init.
+void SetStdioToDevNull(char** argv) {
     // Make stdin/stdout/stderr all point to /dev/null.
     int fd = open("/dev/null", O_RDWR);
     if (fd == -1) {
         int saved_errno = errno;
-        android::base::InitLogging(argv, &android::base::KernelLogger, std::move(abort_function));
+        android::base::InitLogging(argv, &android::base::KernelLogger, InitAborter);
         errno = saved_errno;
         PLOG(FATAL) << "Couldn't open /dev/null";
     }
-    dup2(fd, 0);
-    dup2(fd, 1);
-    dup2(fd, 2);
-    if (fd > 2) close(fd);
-    android::base::InitLogging(argv, &android::base::KernelLogger, std::move(abort_function));
+    dup2(fd, STDIN_FILENO);
+    dup2(fd, STDOUT_FILENO);
+    dup2(fd, STDERR_FILENO);
+    if (fd > STDERR_FILENO) close(fd);
+}
+
+void InitKernelLogging(char** argv) {
+    android::base::InitLogging(argv, &android::base::KernelLogger, InitAborter);
 }
 
 bool IsRecoveryMode() {

init/util.h

@@ -63,7 +63,8 @@ bool is_android_dt_value_expected(const std::string& sub_path, const std::string
 
 bool IsLegalPropertyName(const std::string& name);
 
-void InitKernelLogging(char** argv, std::function<void(const char*)> abort_function);
+void SetStdioToDevNull(char** argv);
+void InitKernelLogging(char** argv);
 bool IsRecoveryMode();
 }  // namespace init
 }  // namespace android