Android: 啟動init.rc 中service的權限問題

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

來啟動init.rc中的service是一個很友善方法來調用某個可執行程式或某個腳本程式

service service_xx  /system/bin/xx

    disabled

    oneshot

但在非AID_ROOT、AID_SYSTEM 使用者的程序中調用ctl.start ctl.stop會碰到權限問題:

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;

}

隻有uid == AID_SYSTEM || uid == AID_ROOT

或符合 control_perms[] = {

    { "dumpstate",AID_SHELL, AID_LOG },

     {NULL, 0, 0 }

}; 的uid程序才有權限star/stop services

是以，如果我們碰到了權限問題，根據log提示，在/system/core/include/private/android_filesystem_config.h

中查到程序定義，添加到control_perms[]清單

比如，uid ==AID_WIFI的某個程式需要權限啟動service_xx

control_perms[] = {

    { "dumpstate",AID_SHELL, AID_LOG },

+  { "service_xx ",AID_WIFI, AID_WIFI},

     {NULL, 0, 0 }

};