vm/native/dalvik_system_Zygote.cpp

/*
 * Copyright (C) 2008 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.
 */

/*
 * dalvik.system.Zygote
 */
#include "Dalvik.h"
#include "native/InternalNativePriv.h"

#ifdef HAVE_SELINUX
#include <selinux/android.h>
#endif

#include <signal.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <grp.h>
#include <errno.h>
#include <paths.h>
#include <sys/personality.h>
#include <sys/stat.h>
#include <sys/mount.h>
#include <linux/fs.h>
#include <cutils/sched_policy.h>
#include <cutils/multiuser.h>
#include <sched.h>

#if defined(HAVE_PRCTL)
# include <sys/prctl.h>
#endif

#define ZYGOTE_LOG_TAG "Zygote"

/* must match values in dalvik.system.Zygote */
enum {
    DEBUG_ENABLE_DEBUGGER           = 1,
    DEBUG_ENABLE_CHECKJNI           = 1 << 1,
    DEBUG_ENABLE_ASSERT             = 1 << 2,
    DEBUG_ENABLE_SAFEMODE           = 1 << 3,
    DEBUG_ENABLE_JNI_LOGGING        = 1 << 4,
};

/* must match values in dalvik.system.Zygote */
enum {
    MOUNT_EXTERNAL_NONE = 0,
    MOUNT_EXTERNAL_SINGLEUSER = 1,
    MOUNT_EXTERNAL_MULTIUSER = 2,
};

/*
 * This signal handler is for zygote mode, since the zygote
 * must reap its children
 */
static void sigchldHandler(int s)
{
    pid_t pid;
    int status;

    while ((pid = waitpid(-1, &status, WNOHANG)) > 0) {
        /* Log process-death status that we care about.  In general it is not
           safe to call ALOG(...) from a signal handler because of possible
           reentrancy.  However, we know a priori that the current implementation
           of ALOG() is safe to call from a SIGCHLD handler in the zygote process.
           If the ALOG() implementation changes its locking strategy or its use
           of syscalls within the lazy-init critical section, its use here may
           become unsafe. */
        if (WIFEXITED(status)) {
            if (WEXITSTATUS(status)) {
                ALOG(LOG_DEBUG, ZYGOTE_LOG_TAG, "Process %d exited cleanly (%d)",
                    (int) pid, WEXITSTATUS(status));
            } else {
                IF_ALOGV(/*should use ZYGOTE_LOG_TAG*/) {
                    ALOG(LOG_VERBOSE, ZYGOTE_LOG_TAG,
                        "Process %d exited cleanly (%d)",
                        (int) pid, WEXITSTATUS(status));
                }
            }
        } else if (WIFSIGNALED(status)) {
            if (WTERMSIG(status) != SIGKILL) {
                ALOG(LOG_DEBUG, ZYGOTE_LOG_TAG,
                    "Process %d terminated by signal (%d)",
                    (int) pid, WTERMSIG(status));
            } else {
                IF_ALOGV(/*should use ZYGOTE_LOG_TAG*/) {
                    ALOG(LOG_VERBOSE, ZYGOTE_LOG_TAG,
                        "Process %d terminated by signal (%d)",
                        (int) pid, WTERMSIG(status));
                }
            }
#ifdef WCOREDUMP
            if (WCOREDUMP(status)) {
                ALOG(LOG_INFO, ZYGOTE_LOG_TAG, "Process %d dumped core",
                    (int) pid);
            }
#endif /* ifdef WCOREDUMP */
        }

        /*
         * If the just-crashed process is the system_server, bring down zygote
         * so that it is restarted by init and system server will be restarted
         * from there.
         */
        if (pid == gDvm.systemServerPid) {
            ALOG(LOG_INFO, ZYGOTE_LOG_TAG,
                "Exit zygote because system server (%d) has terminated",
                (int) pid);
            kill(getpid(), SIGKILL);
        }
    }

    if (pid < 0) {
        ALOG(LOG_WARN, ZYGOTE_LOG_TAG,
            "Zygote SIGCHLD error in waitpid: %s",strerror(errno));
    }
}

/*
 * configure sigchld handler for the zygote process
 * This is configured very late, because earlier in the dalvik lifecycle
 * we can fork() and exec() for the verifier/optimizer, and we
 * want to waitpid() for those rather than have them be harvested immediately.
 *
 * This ends up being called repeatedly before each fork(), but there's
 * no real harm in that.
 */
static void setSignalHandler()
{
    int err;
    struct sigaction sa;

    memset(&sa, 0, sizeof(sa));

    sa.sa_handler = sigchldHandler;

    err = sigaction (SIGCHLD, &sa, NULL);

    if (err < 0) {
        ALOGW("Error setting SIGCHLD handler: %s", strerror(errno));
    }
}

/*
 * Set the SIGCHLD handler back to default behavior in zygote children
 */
static void unsetSignalHandler()
{
    int err;
    struct sigaction sa;

    memset(&sa, 0, sizeof(sa));

    sa.sa_handler = SIG_DFL;

    err = sigaction (SIGCHLD, &sa, NULL);

    if (err < 0) {
        ALOGW("Error unsetting SIGCHLD handler: %s", strerror(errno));
    }
}

/*
 * Calls POSIX setgroups() using the int[] object as an argument.
 * A NULL argument is tolerated.
 */

static int setgroupsIntarray(ArrayObject* gidArray)
{
    gid_t *gids;
    u4 i;
    s4 *contents;

    if (gidArray == NULL) {
        return 0;
    }

    /* just in case gid_t and u4 are different... */
    gids = (gid_t *)alloca(sizeof(gid_t) * gidArray->length);
    contents = (s4 *)(void *)gidArray->contents;

    for (i = 0 ; i < gidArray->length ; i++) {
        gids[i] = (gid_t) contents[i];
    }

    return setgroups((size_t) gidArray->length, gids);
}

/*
 * Sets the resource limits via setrlimit(2) for the values in the
 * two-dimensional array of integers that's passed in. The second dimension
 * contains a tuple of length 3: (resource, rlim_cur, rlim_max). NULL is
 * treated as an empty array.
 *
 * -1 is returned on error.
 */
static int setrlimitsFromArray(ArrayObject* rlimits)
{
    u4 i;
    struct rlimit rlim;

    if (rlimits == NULL) {
        return 0;
    }

    memset (&rlim, 0, sizeof(rlim));

    ArrayObject** tuples = (ArrayObject **)(void *)rlimits->contents;

    for (i = 0; i < rlimits->length; i++) {
        ArrayObject * rlimit_tuple = tuples[i];
        s4* contents = (s4 *)(void *)rlimit_tuple->contents;
        int err;

        if (rlimit_tuple->length != 3) {
            ALOGE("rlimits array must have a second dimension of size 3");
            return -1;
        }

        rlim.rlim_cur = contents[1];
        rlim.rlim_max = contents[2];

        err = setrlimit(contents[0], &rlim);

        if (err < 0) {
            return -1;
        }
    }

    return 0;
}

/*
 * Create private mount space for this process and mount SD card
 * into it, based on active user.  See storage config details at
 * http://source.android.com/tech/storage/
 */
static int mountExternalStorage(uid_t uid, u4 mountExternal) {
    userid_t userid = multiuser_getUserId(uid);

    // Create private mount namespace for our process
    if (unshare(CLONE_NEWNS) == -1) {
        SLOGE("Failed to unshare(): %s", strerror(errno));
        return -1;
    }

    // Mark rootfs as being a slave in our process so that changes
    // from parent namespace flow into our process.
    if (mount("rootfs", "/", NULL, (MS_SLAVE | MS_REC), NULL) == -1) {
        SLOGE("Failed to mount() rootfs as MS_SLAVE: %s", strerror(errno));
        return -1;
    }

    // Create bind mounts to expose external storage
    if (mountExternal == MOUNT_EXTERNAL_MULTIUSER) {
        const char* target_base = getenv("ANDROID_STORAGE");
        const char* target = getenv("EXTERNAL_STORAGE");
        const char* source_base = getenv("MULTIUSER_EXTERNAL_STORAGE");
        if (target_base == NULL || target == NULL || source_base == NULL) {
            SLOGE("Storage environment undefined; unable to provide external storage");
            return -1;
        }

        // Give ourselves a tmpfs staging platform to work with, which obscures
        // any existing shell-specific contents.  Create our mount target, then
        // remount read-only.
        if (mount("tmpfs", target_base, "tmpfs", MS_NOSUID | MS_NODEV,
                "uid=0,gid=1028,mode=0050") == -1) {
            SLOGE("Failed to mount tmpfs to %s: %s", target_base, strerror(errno));
            return -1;
        }
        if (mkdir(target, 0000) == -1) {
            SLOGE("Failed to mkdir %s: %s", target, strerror(errno));
            return -1;
        }
        if (mount("tmpfs", target_base, NULL,
                MS_REMOUNT | MS_RDONLY | MS_NOSUID | MS_NODEV, NULL)) {
            SLOGE("Failed to remount ro %s: %s", target_base, strerror(errno));
            return -1;
        }

        // Mount our user-specific external storage into place, creating path
        // if it doesn't already exist.
        std::string source(StringPrintf("%s/%d", source_base, userid));
        if (access(source.c_str(), F_OK) == -1) {
            if (mkdir(source.c_str(), 0000) == -1) {
                SLOGE("Failed to mkdir %s: %s", source.c_str(), strerror(errno));
                return -1;
            }
        }
        if (mount(source.c_str(), target, NULL, MS_BIND, NULL) == -1) {
            SLOGE("Failed to bind mount %s to %s: %s", source.c_str(), target, strerror(errno));
            return -1;
        }

    } else {
        SLOGE("Mount mode %d unsupported", mountExternal);
        return -1;
    }

    return 0;
}

/* native public static int fork(); */
static void Dalvik_dalvik_system_Zygote_fork(const u4* args, JValue* pResult)
{
    pid_t pid;

    if (!gDvm.zygote) {
        dvmThrowIllegalStateException(
            "VM instance not started with -Xzygote");

        RETURN_VOID();
    }

    if (!dvmGcPreZygoteFork()) {
        ALOGE("pre-fork heap failed");
        dvmAbort();
    }

    setSignalHandler();

    dvmDumpLoaderStats("zygote");
    pid = fork();

#ifdef HAVE_ANDROID_OS
    if (pid == 0) {
        /* child process */
        extern int gMallocLeakZygoteChild;
        gMallocLeakZygoteChild = 1;
    }
#endif

    RETURN_INT(pid);
}

/*
 * Enable/disable debug features requested by the caller.
 *
 * debugger
 *   If set, enable debugging; if not set, disable debugging.  This is
 *   easy to handle, because the JDWP thread isn't started until we call
 *   dvmInitAfterZygote().
 * checkjni
 *   If set, make sure "check JNI" is enabled.
 * assert
 *   If set, make sure assertions are enabled.  This gets fairly weird,
 *   because it affects the result of a method called by class initializers,
 *   and hence can't affect pre-loaded/initialized classes.
 * safemode
 *   If set, operates the VM in the safe mode. The definition of "safe mode" is
 *   implementation dependent and currently only the JIT compiler is disabled.
 *   This is easy to handle because the compiler thread and associated resources
 *   are not requested until we call dvmInitAfterZygote().
 */
static void enableDebugFeatures(u4 debugFlags)
{
    ALOGV("debugFlags is 0x%02x", debugFlags);

    gDvm.jdwpAllowed = ((debugFlags & DEBUG_ENABLE_DEBUGGER) != 0);

    if ((debugFlags & DEBUG_ENABLE_CHECKJNI) != 0) {
        /* turn it on if it's not already enabled */
        dvmLateEnableCheckedJni();
    }

    if ((debugFlags & DEBUG_ENABLE_JNI_LOGGING) != 0) {
        gDvmJni.logThirdPartyJni = true;
    }

    if ((debugFlags & DEBUG_ENABLE_ASSERT) != 0) {
        /* turn it on if it's not already enabled */
        dvmLateEnableAssertions();
    }

    if ((debugFlags & DEBUG_ENABLE_SAFEMODE) != 0) {
#if defined(WITH_JIT)
        /* turn off the jit if it is explicitly requested by the app */
        if (gDvm.executionMode == kExecutionModeJit)
            gDvm.executionMode = kExecutionModeInterpFast;
#endif
    }

#ifdef HAVE_ANDROID_OS
    if ((debugFlags & DEBUG_ENABLE_DEBUGGER) != 0) {
        /* To let a non-privileged gdbserver attach to this
         * process, we must set its dumpable bit flag. However
         * we are not interested in generating a coredump in
         * case of a crash, so also set the coredump size to 0
         * to disable that
         */
        if (prctl(PR_SET_DUMPABLE, 1, 0, 0, 0) < 0) {
            ALOGE("could not set dumpable bit flag for pid %d: %s",
                 getpid(), strerror(errno));
        } else {
            struct rlimit rl;
            rl.rlim_cur = 0;
            rl.rlim_max = RLIM_INFINITY;
            if (setrlimit(RLIMIT_CORE, &rl) < 0) {
                ALOGE("could not disable core file generation for pid %d: %s",
                    getpid(), strerror(errno));
            }
        }
    }
#endif
}

/*
 * Set Linux capability flags.
 *
 * Returns 0 on success, errno on failure.
 */
static int setCapabilities(int64_t permitted, int64_t effective)
{
#ifdef HAVE_ANDROID_OS
    struct __user_cap_header_struct capheader;
    struct __user_cap_data_struct capdata;

    memset(&capheader, 0, sizeof(capheader));
    memset(&capdata, 0, sizeof(capdata));

    capheader.version = _LINUX_CAPABILITY_VERSION;
    capheader.pid = 0;

    capdata.effective = effective;
    capdata.permitted = permitted;

    ALOGV("CAPSET perm=%llx eff=%llx", permitted, effective);
    if (capset(&capheader, &capdata) != 0)
        return errno;
#endif /*HAVE_ANDROID_OS*/

    return 0;
}

#ifdef HAVE_SELINUX
/*
 * Set SELinux security context.
 *
 * Returns 0 on success, -1 on failure.
 */
static int setSELinuxContext(uid_t uid, bool isSystemServer,
                             const char *seInfo, const char *niceName)
{
#ifdef HAVE_ANDROID_OS
    return selinux_android_setcontext(uid, isSystemServer, seInfo, niceName);
#else
    return 0;
#endif
}
#endif

/*
 * Utility routine to fork zygote and specialize the child process.
 */
static pid_t forkAndSpecializeCommon(const u4* args, bool isSystemServer)
{
    pid_t pid;

    uid_t uid = (uid_t) args[0];
    gid_t gid = (gid_t) args[1];
    ArrayObject* gids = (ArrayObject *)args[2];
    u4 debugFlags = args[3];
    ArrayObject *rlimits = (ArrayObject *)args[4];
    u4 mountExternal = MOUNT_EXTERNAL_NONE;
    int64_t permittedCapabilities, effectiveCapabilities;
#ifdef HAVE_SELINUX
    char *seInfo = NULL;
    char *niceName = NULL;
#endif

    if (isSystemServer) {
        /*
         * Don't use GET_ARG_LONG here for now.  gcc is generating code
         * that uses register d8 as a temporary, and that's coming out
         * scrambled in the child process.  b/3138621
         */
        //permittedCapabilities = GET_ARG_LONG(args, 5);
        //effectiveCapabilities = GET_ARG_LONG(args, 7);
        permittedCapabilities = args[5] | (int64_t) args[6] << 32;
        effectiveCapabilities = args[7] | (int64_t) args[8] << 32;
    } else {
        mountExternal = args[5];
        permittedCapabilities = effectiveCapabilities = 0;
#ifdef HAVE_SELINUX
        StringObject* seInfoObj = (StringObject*)args[6];
        if (seInfoObj) {
            seInfo = dvmCreateCstrFromString(seInfoObj);
            if (!seInfo) {
                ALOGE("seInfo dvmCreateCstrFromString failed");
                dvmAbort();
            }
        }
        StringObject* niceNameObj = (StringObject*)args[7];
        if (niceNameObj) {
            niceName = dvmCreateCstrFromString(niceNameObj);
            if (!niceName) {
                ALOGE("niceName dvmCreateCstrFromString failed");
                dvmAbort();
            }
        }
#endif
    }

    if (!gDvm.zygote) {
        dvmThrowIllegalStateException(
            "VM instance not started with -Xzygote");

        return -1;
    }

    if (!dvmGcPreZygoteFork()) {
        ALOGE("pre-fork heap failed");
        dvmAbort();
    }

    setSignalHandler();

    dvmDumpLoaderStats("zygote");
    pid = fork();

    if (pid == 0) {
        int err;
        /* The child process */

#ifdef HAVE_ANDROID_OS
        extern int gMallocLeakZygoteChild;
        gMallocLeakZygoteChild = 1;

        /* keep caps across UID change, unless we're staying root */
        if (uid != 0) {
            err = prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0);

            if (err < 0) {
                ALOGE("cannot PR_SET_KEEPCAPS: %s", strerror(errno));
                dvmAbort();
            }
        }

#endif /* HAVE_ANDROID_OS */

        if (mountExternal != MOUNT_EXTERNAL_NONE) {
            err = mountExternalStorage(uid, mountExternal);
            if (err < 0) {
                ALOGE("cannot mountExternalStorage(): %s", strerror(errno));
                if (errno == ENOTCONN || errno == EROFS) {
                    // Missing FUSE daemon, which is expected when booting encrypted
                    // devices; let Zygote continue without external storage.
                } else {
                    dvmAbort();
                }
            }
        }

        err = setgroupsIntarray(gids);
        if (err < 0) {
            ALOGE("cannot setgroups(): %s", strerror(errno));
            dvmAbort();
        }

        err = setrlimitsFromArray(rlimits);
        if (err < 0) {
            ALOGE("cannot setrlimit(): %s", strerror(errno));
            dvmAbort();
        }

        err = setgid(gid);
        if (err < 0) {
            ALOGE("cannot setgid(%d): %s", gid, strerror(errno));
            dvmAbort();
        }

        err = setuid(uid);
        if (err < 0) {
            ALOGE("cannot setuid(%d): %s", uid, strerror(errno));
            dvmAbort();
        }

        int current = personality(0xffffFFFF);
        int success = personality((ADDR_NO_RANDOMIZE | current));
        if (success == -1) {
          ALOGW("Personality switch failed. current=%d error=%d\n", current, errno);
        }

        err = setCapabilities(permittedCapabilities, effectiveCapabilities);
        if (err != 0) {
            ALOGE("cannot set capabilities (%llx,%llx): %s",
                permittedCapabilities, effectiveCapabilities, strerror(err));
            dvmAbort();
        }

        err = set_sched_policy(0, SP_DEFAULT);
        if (err < 0) {
            ALOGE("cannot set_sched_policy(0, SP_DEFAULT): %s", strerror(-err));
            dvmAbort();
        }

#ifdef HAVE_SELINUX
        err = setSELinuxContext(uid, isSystemServer, seInfo, niceName);
        if (err < 0) {
            ALOGE("cannot set SELinux context: %s\n", strerror(errno));
            dvmAbort();
        }
        // These free(3) calls are safe because we know we're only ever forking
        // a single-threaded process, so we know no other thread held the heap
        // lock when we forked.
        free(seInfo);
        free(niceName);
#endif

        /*
         * Our system thread ID has changed.  Get the new one.
         */
        Thread* thread = dvmThreadSelf();
        thread->systemTid = dvmGetSysThreadId();

        /* configure additional debug options */
        enableDebugFeatures(debugFlags);

        unsetSignalHandler();
        gDvm.zygote = false;
        if (!dvmInitAfterZygote()) {
            ALOGE("error in post-zygote initialization");
            dvmAbort();
        }
    } else if (pid > 0) {
        /* the parent process */
#ifdef HAVE_SELINUX
        free(seInfo);
        free(niceName);
#endif
    }

    return pid;
}

/*
 * native public static int nativeForkAndSpecialize(int uid, int gid,
 *     int[] gids, int debugFlags, int[][] rlimits, int mountExternal,
 *     String seInfo, String niceName);
 */
static void Dalvik_dalvik_system_Zygote_forkAndSpecialize(const u4* args,
    JValue* pResult)
{
    pid_t pid;

    pid = forkAndSpecializeCommon(args, false);

    RETURN_INT(pid);
}

/*
 * native public static int nativeForkSystemServer(int uid, int gid,
 *     int[] gids, int debugFlags, int[][] rlimits,
 *     long permittedCapabilities, long effectiveCapabilities);
 */
static void Dalvik_dalvik_system_Zygote_forkSystemServer(
        const u4* args, JValue* pResult)
{
    pid_t pid;
    pid = forkAndSpecializeCommon(args, true);

    /* The zygote process checks whether the child process has died or not. */
    if (pid > 0) {
        int status;

        ALOGI("System server process %d has been created", pid);
        gDvm.systemServerPid = pid;
        /* There is a slight window that the system server process has crashed
         * but it went unnoticed because we haven't published its pid yet. So
         * we recheck here just to make sure that all is well.
         */
        if (waitpid(pid, &status, WNOHANG) == pid) {
            ALOGE("System server process %d has died. Restarting Zygote!", pid);
            kill(getpid(), SIGKILL);
        }
    }
    RETURN_INT(pid);
}

/* native private static void nativeExecShell(String command);
 */
static void Dalvik_dalvik_system_Zygote_execShell(
        const u4* args, JValue* pResult)
{
    StringObject* command = (StringObject*)args[0];

    const char *argp[] = {_PATH_BSHELL, "-c", NULL, NULL};
    argp[2] = dvmCreateCstrFromString(command);

    ALOGI("Exec: %s %s %s", argp[0], argp[1], argp[2]);

    execv(_PATH_BSHELL, (char**)argp);
    exit(127);
}

const DalvikNativeMethod dvm_dalvik_system_Zygote[] = {
    { "nativeFork", "()I",
      Dalvik_dalvik_system_Zygote_fork },
    { "nativeForkAndSpecialize", "(II[II[[IILjava/lang/String;Ljava/lang/String;)I",
      Dalvik_dalvik_system_Zygote_forkAndSpecialize },
    { "nativeForkSystemServer", "(II[II[[IJJ)I",
      Dalvik_dalvik_system_Zygote_forkSystemServer },
    { "nativeExecShell", "(Ljava/lang/String;)V",
      Dalvik_dalvik_system_Zygote_execShell },
    { NULL, NULL, NULL },
};