Android應用安裝過程分析（二）

上次說到initView的兩句核心代碼，installPackageWithVerificationAndEncryption函數和installExistingPackage函數。

而成員pm是一個PackageManager類型的變量，這是一個接口類，具體的實現代碼在PackageManagerService中

 

    public void installPackageWithVerificationAndEncryption(Uri packageURI,
            IPackageInstallObserver observer, int flags, String installerPackageName,
            VerificationParams verificationParams, ContainerEncryptionParams encryptionParams) {
        mContext.enforceCallingOrSelfPermission(android.Manifest.permission.INSTALL_PACKAGES,
                null);

        final int uid = Binder.getCallingUid();
        if (isUserRestricted(UserHandle.getUserId(uid), UserManager.DISALLOW_INSTALL_APPS)) {
            try {
                observer.packageInstalled("", PackageManager.INSTALL_FAILED_USER_RESTRICTED);
            } catch (RemoteException re) {
            }
            return;
        }

        UserHandle user;
        if ((flags&PackageManager.INSTALL_ALL_USERS) != 0) {
            user = UserHandle.ALL;
        } else {
            user = new UserHandle(UserHandle.getUserId(uid));
        }

        final int filteredFlags;

        if (uid == Process.SHELL_UID || uid == 0) {
            if (DEBUG_INSTALL) {
                Slog.v(TAG, "Install from ADB");
            }
            filteredFlags = flags | PackageManager.INSTALL_FROM_ADB;
        } else {
            filteredFlags = flags & ~PackageManager.INSTALL_FROM_ADB;
        }

        verificationParams.setInstallerUid(uid);

        final Message msg = mHandler.obtainMessage(INIT_COPY);
        msg.obj = new InstallParams(packageURI, observer, filteredFlags, installerPackageName,
                verificationParams, encryptionParams, user);
        mHandler.sendMessage(msg);
    }

在Android中，PackageManager負責管理安裝包的信息，但是應用的安裝和卸載是PackageManager訪問installd服務來獲得

 

int res = mInstaller.install(packageName, uid, uid, seinfo);

這是PackageManager中的代碼

 

mInstaller來自Installer

 

    public int install(String name, int uid, int gid, String seinfo) {
        StringBuilder builder = new StringBuilder("install");
        builder.append(' ');
        builder.append(name);
        builder.append(' ');
        builder.append(uid);
        builder.append(' ');
        builder.append(gid);
        builder.append(' ');
        builder.append(seinfo != null ? seinfo : "!");
        return execute(builder.toString());
    }

install中調用execute

 

 

    private int execute(String cmd) {
        String res = transaction(cmd);
        try {
            return Integer.parseInt(res);
        } catch (NumberFormatException ex) {
            return -1;
        }
    }

再調用transaction

 

 

    private synchronized String transaction(String cmd) {
        if (!connect()) {
            Slog.e(TAG, "connection failed");
            return "-1";
        }

        if (!writeCommand(cmd)) {
            /*
             * If installd died and restarted in the background (unlikely but
             * possible) we'll fail on the next write (this one). Try to
             * reconnect and write the command one more time before giving up.
             */
            Slog.e(TAG, "write command failed? reconnect!");
            if (!connect() || !writeCommand(cmd)) {
                return "-1";
            }
        }
        if (LOCAL_DEBUG) {
            Slog.i(TAG, "send: '" + cmd + "'");
        }
        if (readReply()) {
            String s = new String(buf, 0, buflen);
            if (LOCAL_DEBUG) {
                Slog.i(TAG, "recv: '" + s + "'");
            }
            return s;
        } else {
            if (LOCAL_DEBUG) {
                Slog.i(TAG, "fail");
            }
            return "-1";
        }
    }

可以看到首先通過connect函數進行連接

 

 

    private boolean connect() {
        if (mSocket != null) {
            return true;
        }
        Slog.i(TAG, "connecting...");
        try {
            mSocket = new LocalSocket();

            LocalSocketAddress address = new LocalSocketAddress("installd",
                    LocalSocketAddress.Namespace.RESERVED);

            mSocket.connect(address);

            mIn = mSocket.getInputStream();
            mOut = mSocket.getOutputStream();
        } catch (IOException ex) {
            disconnect();
            return false;
        }
        return true;
    }

 

address指向的就是install服務，通過LocalSocket本地套接字。此外還有輸入輸出流

 

public final class Installer {
    private static final String TAG = "Installer";

    private static final boolean LOCAL_DEBUG = false;

    InputStream mIn;

    OutputStream mOut;

    LocalSocket mSocket;

    byte buf[] = new byte[1024];

    int buflen = 0;

connect連接成功後使用writeCommand函數將內容寫入通信流當中

 

 

    private boolean writeCommand(String _cmd) {
        byte[] cmd = _cmd.getBytes();
        int len = cmd.length;
        if ((len < 1) || (len > 1024))
            return false;
        buf[0] = (byte) (len & 0xff);
        buf[1] = (byte) ((len >> 8) & 0xff);
        try {
            mOut.write(buf, 0, 2);
            mOut.write(cmd, 0, len);
        } catch (IOException ex) {
            Slog.e(TAG, "write error");
            disconnect();
            return false;
        }
        return true;
    }

脈絡很清楚pm ——> PackageManagerServer ——> Installer.install ——>通過LocalSocket ——> Installd
相關文件位置

 

frameworks\native\cmds\installd\installd.c

frameworks\base\services\java\com\android\server\pm\PackageManagerService.java

frameworks\base\services\java\com\android\server\pm\Installer.java

下面著重關注一下installd

主函數

 

int main(const int argc, const char *argv[]) {
    char buf[BUFFER_MAX];
    struct sockaddr addr;
    socklen_t alen;
    int lsocket, s, count;

    ALOGI("installd firing up\n");

    if (initialize_globals() < 0) {	//初始化全局變量
        ALOGE("Could not initialize globals; exiting.\n");
        exit(1);
    }

    if (initialize_directories() < 0) {	//初始化安裝目錄
        ALOGE("Could not create directories; exiting.\n");
        exit(1);
    }

    drop_privileges();	//權限限制

    lsocket = android_get_control_socket(SOCKET_PATH);	//取得套接字句柄
    if (lsocket < 0) {
        ALOGE("Failed to get socket from environment: %s\n", strerror(errno));
        exit(1);
    }
    if (listen(lsocket, 5)) {	//監聽socket
        ALOGE("Listen on socket failed: %s\n", strerror(errno));
        exit(1);
    }
    fcntl(lsocket, F_SETFD, FD_CLOEXEC);	//修改socket的屬性

    for (;;) {	//循環等待客戶端的消息
        alen = sizeof(addr);
        s = accept(lsocket, &addr, &alen);
        if (s < 0) {
            ALOGE("Accept failed: %s\n", strerror(errno));
            continue;
        }
        fcntl(s, F_SETFD, FD_CLOEXEC);

        ALOGI("new connection\n");
        for (;;) {	//循環讀取內容
            unsigned short count;
	    //客戶端數據的格式為  | 數據長度 | 數據內容 |
	    //讀取頭四個字節獲得長度
            if (readx(s, &count, sizeof(count))) {
                ALOGE("failed to read size\n");
                break;
            }
	    //判斷長度的合法性
            if ((count < 1) || (count >= BUFFER_MAX)) {
                ALOGE("invalid size %d\n", count);
                break;
            }
	    //讀取全部內容
            if (readx(s, buf, count)) {
                ALOGE("failed to read command\n");
                break;
            }
	    //執行
            buf[count] = 0;
            if (execute(s, buf)) break;
        }
        ALOGI("closing connection\n");
        close(s);
    }

    return 0;
}

全局變量的初始化函數initialize_globals

int initialize_globals() {
    // Get the android data directory.
    if (get_path_from_env(&android_data_dir, "ANDROID_DATA") < 0) {
        return -1;
    }

    // Get the android app directory.
    if (copy_and_append(&android_app_dir, &android_data_dir, APP_SUBDIR) < 0) {
        return -1;
    }

    // Get the android protected app directory.
    if (copy_and_append(&android_app_private_dir, &android_data_dir, PRIVATE_APP_SUBDIR) < 0) {
        return -1;
    }

    // Get the android app native library directory.
    if (copy_and_append(&android_app_lib_dir, &android_data_dir, APP_LIB_SUBDIR) < 0) {
        return -1;
    }

    // Get the sd-card ASEC mount point.
    if (get_path_from_env(&android_asec_dir, "ASEC_MOUNTPOINT") < 0) {
        return -1;
    }

    // Get the android media directory.
    if (copy_and_append(&android_media_dir, &android_data_dir, MEDIA_SUBDIR) < 0) {
        return -1;
    }

    // Take note of the system and vendor directories.
    android_system_dirs.count = 2;

    android_system_dirs.dirs = calloc(android_system_dirs.count, sizeof(dir_rec_t));
    if (android_system_dirs.dirs == NULL) {
        ALOGE("Couldn't allocate array for dirs; aborting\n");
        return -1;
    }

    // system
    if (get_path_from_env(&android_system_dirs.dirs[0], "ANDROID_ROOT") < 0) {
        free_globals();
        return -1;
    }

    // append "app/" to dirs[0]
    char *system_app_path = build_string2(android_system_dirs.dirs[0].path, APP_SUBDIR);
    android_system_dirs.dirs[0].path = system_app_path;
    android_system_dirs.dirs[0].len = strlen(system_app_path);

    // vendor
    // TODO replace this with an environment variable (doesn't exist yet)
    android_system_dirs.dirs[1].path = "/vendor/app/";
    android_system_dirs.dirs[1].len = strlen(android_system_dirs.dirs[1].path);

    return 0;
}

全局變量位於同目錄下的installd.h文件，部分變量如下所示

 

 

typedef struct {
    char* path;
    size_t len;
} dir_rec_t;

typedef struct {
    size_t count;
    dir_rec_t* dirs;
} dir_rec_array_t;

extern dir_rec_t android_app_dir;
extern dir_rec_t android_app_private_dir;
extern dir_rec_t android_app_lib_dir;
extern dir_rec_t android_data_dir;
extern dir_rec_t android_asec_dir;
extern dir_rec_t android_media_dir;
extern dir_rec_array_t android_system_dirs;

此外這當中的一些函數比如copy_and_append，也位於同目錄下的utils.c

 

 

int copy_and_append(dir_rec_t* dst, const dir_rec_t* src, const char* suffix) {
    dst->len = src->len + strlen(suffix);
    const size_t dstSize = dst->len + 1;
    dst->path = (char*) malloc(dstSize);

    if (dst->path == NULL
            || snprintf(dst->path, dstSize, "%s%s", src->path, suffix)
                    != (ssize_t) dst->len) {
        ALOGE("Could not allocate memory to hold appended path; aborting\n");
        return -1;
    }

    return 0;
}

之後是初始化安裝目錄initialize_directories

 

 

int initialize_directories() {
    int res = -1;

    // Read current filesystem layout version to handle upgrade paths
    char version_path[PATH_MAX];
    snprintf(version_path, PATH_MAX, "%s.layout_version", android_data_dir.path);

    int oldVersion;
    if (fs_read_atomic_int(version_path, &oldVersion) == -1) {
        oldVersion = 0;
    }
    int version = oldVersion;

    // /data/user
    char *user_data_dir = build_string2(android_data_dir.path, SECONDARY_USER_PREFIX);
    // /data/data
    char *legacy_data_dir = build_string2(android_data_dir.path, PRIMARY_USER_PREFIX);
    // /data/user/0
    char *primary_data_dir = build_string3(android_data_dir.path, SECONDARY_USER_PREFIX, "0");
    if (!user_data_dir || !legacy_data_dir || !primary_data_dir) {
        goto fail;
    }

    // Make the /data/user directory if necessary
    if (access(user_data_dir, R_OK) < 0) {
        if (mkdir(user_data_dir, 0711) < 0) {
            goto fail;
        }
        if (chown(user_data_dir, AID_SYSTEM, AID_SYSTEM) < 0) {
            goto fail;
        }
        if (chmod(user_data_dir, 0711) < 0) {
            goto fail;
        }
    }
    // Make the /data/user/0 symlink to /data/data if necessary
    if (access(primary_data_dir, R_OK) < 0) {
        if (symlink(legacy_data_dir, primary_data_dir)) {
            goto fail;
        }
    }

    if (version == 0) {
        // Introducing multi-user, so migrate /data/media contents into /data/media/0
        ALOGD("Upgrading /data/media for multi-user");

        // Ensure /data/media
        if (fs_prepare_dir(android_media_dir.path, 0770, AID_MEDIA_RW, AID_MEDIA_RW) == -1) {
            goto fail;
        }

        // /data/media.tmp
        char media_tmp_dir[PATH_MAX];
        snprintf(media_tmp_dir, PATH_MAX, "%smedia.tmp", android_data_dir.path);

        // Only copy when upgrade not already in progress
        if (access(media_tmp_dir, F_OK) == -1) {
            if (rename(android_media_dir.path, media_tmp_dir) == -1) {
                ALOGE("Failed to move legacy media path: %s", strerror(errno));
                goto fail;
            }
        }

        // Create /data/media again
        if (fs_prepare_dir(android_media_dir.path, 0770, AID_MEDIA_RW, AID_MEDIA_RW) == -1) {
            goto fail;
        }

        // /data/media/0
        char owner_media_dir[PATH_MAX];
        snprintf(owner_media_dir, PATH_MAX, "%s0", android_media_dir.path);

        // Move any owner data into place
        if (access(media_tmp_dir, F_OK) == 0) {
            if (rename(media_tmp_dir, owner_media_dir) == -1) {
                ALOGE("Failed to move owner media path: %s", strerror(errno));
                goto fail;
            }
        }

        // Ensure media directories for any existing users
        DIR *dir;
        struct dirent *dirent;
        char user_media_dir[PATH_MAX];

        dir = opendir(user_data_dir);
        if (dir != NULL) {
            while ((dirent = readdir(dir))) {
                if (dirent->d_type == DT_DIR) {
                    const char *name = dirent->d_name;

                    // skip "." and ".."
                    if (name[0] == '.') {
                        if (name[1] == 0) continue;
                        if ((name[1] == '.') && (name[2] == 0)) continue;
                    }

                    // /data/media/
                    snprintf(user_media_dir, PATH_MAX, "%s%s", android_media_dir.path, name);
                    if (fs_prepare_dir(user_media_dir, 0770, AID_MEDIA_RW, AID_MEDIA_RW) == -1) {
                        goto fail;
                    }
                }
            }
            closedir(dir);
        }

        version = 1;
    }

    // /data/media/obb
    char media_obb_dir[PATH_MAX];
    snprintf(media_obb_dir, PATH_MAX, "%sobb", android_media_dir.path);

    if (version == 1) {
        // Introducing /data/media/obb for sharing OBB across users; migrate
        // any existing OBB files from owner.
        ALOGD("Upgrading to shared /data/media/obb");

        // /data/media/0/Android/obb
        char owner_obb_path[PATH_MAX];
        snprintf(owner_obb_path, PATH_MAX, "%s0/Android/obb", android_media_dir.path);

        // Only move if target doesn't already exist
        if (access(media_obb_dir, F_OK) != 0 && access(owner_obb_path, F_OK) == 0) {
            if (rename(owner_obb_path, media_obb_dir) == -1) {
                ALOGE("Failed to move OBB from owner: %s", strerror(errno));
                goto fail;
            }
        }

        version = 2;
    }

    if (ensure_media_user_dirs(0) == -1) {
        ALOGE("Failed to setup media for user 0");
        goto fail;
    }
    if (fs_prepare_dir(media_obb_dir, 0770, AID_MEDIA_RW, AID_MEDIA_RW) == -1) {
        goto fail;
    }

    // Persist layout version if changed
    if (version != oldVersion) {
        if (fs_write_atomic_int(version_path, version) == -1) {
            ALOGE("Failed to save version to %s: %s", version_path, strerror(errno));
            goto fail;
        }
    }

    // Success!
    res = 0;

fail:
    free(user_data_dir);
    free(legacy_data_dir);
    free(primary_data_dir);
    return res;
}

然後drop_privileges，用於設置權限

 

 

static void drop_privileges() {
    if (prctl(PR_SET_KEEPCAPS, 1) < 0) {
        ALOGE("prctl(PR_SET_KEEPCAPS) failed: %s\n", strerror(errno));
        exit(1);
    }

    if (setgid(AID_INSTALL) < 0) {
        ALOGE("setgid() can't drop privileges; exiting.\n");
        exit(1);
    }

    if (setuid(AID_INSTALL) < 0) {
        ALOGE("setuid() can't drop privileges; exiting.\n");
        exit(1);
    }

    struct __user_cap_header_struct capheader;
    struct __user_cap_data_struct capdata[2];
    memset(&capheader, 0, sizeof(capheader));
    memset(&capdata, 0, sizeof(capdata));
    capheader.version = _LINUX_CAPABILITY_VERSION_3;
    capheader.pid = 0;

    capdata[CAP_TO_INDEX(CAP_DAC_OVERRIDE)].permitted |= CAP_TO_MASK(CAP_DAC_OVERRIDE);
    capdata[CAP_TO_INDEX(CAP_CHOWN)].permitted        |= CAP_TO_MASK(CAP_CHOWN);
    capdata[CAP_TO_INDEX(CAP_SETUID)].permitted       |= CAP_TO_MASK(CAP_SETUID);
    capdata[CAP_TO_INDEX(CAP_SETGID)].permitted       |= CAP_TO_MASK(CAP_SETGID);

    capdata[0].effective = capdata[0].permitted;
    capdata[1].effective = capdata[1].permitted;
    capdata[0].inheritable = 0;
    capdata[1].inheritable = 0;

    if (capset(&capheader, &capdata[0]) < 0) {
        ALOGE("capset failed: %s\n", strerror(errno));
        exit(1);
    }
}

這當中包含了gid和uid的設定

 

執行函數execute

 

static int execute(int s, char cmd[BUFFER_MAX])
{
    char reply[REPLY_MAX];
    char *arg[TOKEN_MAX+1];
    unsigned i;
    unsigned n = 0;
    unsigned short count;
    int ret = -1;

//    ALOGI("execute('%s')\n", cmd);

        /* default reply is "" */
    reply[0] = 0;

        /* n is number of args (not counting arg[0]) */
    arg[0] = cmd;
    while (*cmd) {
        if (isspace(*cmd)) {
            *cmd++ = 0;
            n++;
            arg[n] = cmd;
            if (n == TOKEN_MAX) {
                ALOGE("too many arguments\n");
                goto done;
            }
        }
        cmd++;
    }
    //與cmds中保存的命令進行匹配，並且要檢查參數個數是否符合要求
    for (i = 0; i < sizeof(cmds) / sizeof(cmds[0]); i++) {
        if (!strcmp(cmds[i].name,arg[0])) {
            if (n != cmds[i].numargs) {
                ALOGE("%s requires %d arguments (%d given)\n",
                     cmds[i].name, cmds[i].numargs, n);
            } else {
                ret = cmds[i].func(arg + 1, reply);
            }
            goto done;
        }
    }
    ALOGE("unsupported command '%s'\n", arg[0]);

done:
    if (reply[0]) {
        n = snprintf(cmd, BUFFER_MAX, "%d %s", ret, reply);
    } else {
        n = snprintf(cmd, BUFFER_MAX, "%d", ret);
    }
    if (n > BUFFER_MAX) n = BUFFER_MAX;
    count = n;

//    ALOGI("reply: '%s'\n", cmd);
    if (writex(s, &count, sizeof(count))) return -1;
    if (writex(s, cmd, count)) return -1;
    return 0;
}

函數很簡單。。。

 

cmds的內容

 

struct cmdinfo cmds[] = {
    { "ping",                 0, do_ping },
    { "install",              4, do_install },
    { "dexopt",               3, do_dexopt },
    { "movedex",              2, do_move_dex },
    { "rmdex",                1, do_rm_dex },
    { "remove",               2, do_remove },
    { "rename",               2, do_rename },
    { "fixuid",               3, do_fixuid },
    { "freecache",            1, do_free_cache },
    { "rmcache",              2, do_rm_cache },
    { "getsize",              6, do_get_size },
    { "rmuserdata",           2, do_rm_user_data },
    { "movefiles",            0, do_movefiles },
    { "linklib",              3, do_linklib },
    { "mkuserdata",           3, do_mk_user_data },
    { "rmuser",               1, do_rm_user },
};

第一列是命令字符串，第二列是該命令的參數個數，第三列是函數指針。

 

cmdinfo結構

 

struct cmdinfo {
    const char *name;
    unsigned numargs;
    int (*func)(char **arg, char reply[REPLY_MAX]);
};

 

這些do開頭的函數只是對真正執行函數的一個簡單封裝，比如do_install

 

static int do_install(char **arg, char reply[REPLY_MAX])
{
    return install(arg[0], atoi(arg[1]), atoi(arg[2]), arg[3]); /* pkgname, uid, gid, seinfo */
}

而真正的執行函數都保存在同目錄下的commands.c文件中

 

 

int install(const char *pkgname, uid_t uid, gid_t gid, const char *seinfo)
{
    char pkgdir[PKG_PATH_MAX];
    char libsymlink[PKG_PATH_MAX];
    char applibdir[PKG_PATH_MAX];
    struct stat libStat;

    if ((uid < AID_SYSTEM) || (gid < AID_SYSTEM)) {
        ALOGE("invalid uid/gid: %d %d\n", uid, gid);
        return -1;
    }

    if (create_pkg_path(pkgdir, pkgname, PKG_DIR_POSTFIX, 0)) {
        ALOGE("cannot create package path\n");
        return -1;
    }

    if (create_pkg_path(libsymlink, pkgname, PKG_LIB_POSTFIX, 0)) {
        ALOGE("cannot create package lib symlink origin path\n");
        return -1;
    }

    if (create_pkg_path_in_dir(applibdir, &android_app_lib_dir, pkgname, PKG_DIR_POSTFIX)) {
        ALOGE("cannot create package lib symlink dest path\n");
        return -1;
    }

    if (mkdir(pkgdir, 0751) < 0) {
        ALOGE("cannot create dir '%s': %s\n", pkgdir, strerror(errno));
        return -1;
    }
    if (chmod(pkgdir, 0751) < 0) {
        ALOGE("cannot chmod dir '%s': %s\n", pkgdir, strerror(errno));
        unlink(pkgdir);
        return -1;
    }

    if (lstat(libsymlink, &libStat) < 0) {
        if (errno != ENOENT) {
            ALOGE("couldn't stat lib dir: %s\n", strerror(errno));
            return -1;
        }
    } else {
        if (S_ISDIR(libStat.st_mode)) {
            if (delete_dir_contents(libsymlink, 1, 0) < 0) {
                ALOGE("couldn't delete lib directory during install for: %s", libsymlink);
                return -1;
            }
        } else if (S_ISLNK(libStat.st_mode)) {
            if (unlink(libsymlink) < 0) {
                ALOGE("couldn't unlink lib directory during install for: %s", libsymlink);
                return -1;
            }
        }
    }

    if (symlink(applibdir, libsymlink) < 0) {
        ALOGE("couldn't symlink directory '%s' -> '%s': %s\n", libsymlink, applibdir,
                strerror(errno));
        unlink(pkgdir);
        return -1;
    }

    if (selinux_android_setfilecon2(pkgdir, pkgname, seinfo, uid) < 0) {
        ALOGE("cannot setfilecon dir '%s': %s\n", pkgdir, strerror(errno));
        unlink(libsymlink);
        unlink(pkgdir);
        return -errno;
    }

    if (chown(pkgdir, uid, gid) < 0) {
        ALOGE("cannot chown dir '%s': %s\n", pkgdir, strerror(errno));
        unlink(libsymlink);
        unlink(pkgdir);
        return -1;
    }

    return 0;
}