Android: 启动init.rc 中service的权限问题

通过property_set("ctl.start", service_xx);

来启动init.rc中的service是一个很方便方法来调用某个可执行程序或某个脚本程序

service service_xx/system/bin/xx

disabled
oneshot

但在非AID_ROOT、AID_SYSTEM 用户的进程中调用ctl.start ctl.stop会碰到权限问题:

system/core/init/property_service.c

/*
 * White list of UID that are allowed to start/stop services.
 * Currently there are no user apps that require.
 */
struct {
    const char *service;
    unsigned int uid;
    unsigned int gid;
} control_perms[] = {
    { "dumpstate",AID_SHELL, AID_LOG },
     {NULL, 0, 0 }
};

/*
 * Checks permissions for starting/stoping system services.
 * AID_SYSTEM and AID_ROOT are always allowed.
 *
 * Returns 1 if uid allowed, 0 otherwise.
 */
static int check_control_perms(const char *name, int uid, int gid) {
    int i;
    if (uid == AID_SYSTEM || uid == AID_ROOT)
        return 1;

    /* Search the ACL */
    for (i = 0; control_perms[i].service; i++) {
        if (strcmp(control_perms[i].service, name) == 0) {
            if ((uid && control_perms[i].uid == uid) ||
                (gid && control_perms[i].gid == gid)) {
                return 1;
            }
        }
    }
    return 0;
}

只有uid == AID_SYSTEM || uid == AID_ROOT

或符合 control_perms[] = {
{ "dumpstate",AID_SHELL, AID_LOG },
{NULL, 0, 0 }
}; 的uid进程才有权限star/stop services

因此，如果我们碰到了权限问题，根据log提示，在/system/core/include/private/android_filesystem_config.h

中查到进程定义，添加到control_perms[]列表

比如，uid ==AID_WIFI的某个程序需要权限启动service_xx

control_perms[] = {
{ "dumpstate",AID_SHELL, AID_LOG },

+ { "service_xx",AID_WIFI, AID_WIFI},
{NULL, 0, 0 }
};