Android Permission
1. 文件(夹)读写权限
init.rc 中建立test1 test2 test3 文件夹
mkdir /data/misc/test1 0770 root root
mkdir /data/misc/test2 0770 wifi wifi
mkdir /data/misc/test3 0770 system misc
其中
test1 目录的owner是root, group 也是root
test2 目录的owner是wifi , group 也是wifi
test3 目录的owner是system , group 是misc （任何用户都属于group misc）
service xxxx /system/bin/xxxx
user root
disabled
oneshot
service yyyy /system/bin/yyyy
user system
disabled
oneshot
service zzzz /system/bin/zzzz
user wifi
disabled
oneshot
结果:
xxxx 服务可以访问 test1, test2, test3
yyyy 服务可以访问 test3
zzzz 服务可以访问 test2, test3
Android 中mkdir 的定义
int do_mkdir(int nargs, char **args) { mode_t mode = 0755; /* mkdir
2. Property 权限
Android Property 也是有权限的。
2.1 以前缀 ctl. 开头的控制属性， 设置前，Android 代码会调用函数check_control_perms()检查调用者的 user id 和 group id
struct { const char *service; unsigned int uid; unsigned int gid; } control_perms[] = { { "dumpstate",AID_SHELL, AID_LOG }, {NULL, 0, 0 } }; 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; }
2.2 其它属性， 设置前，Android 代码会调用函数check_perms()检查调用者的 user id 和 group id
check_perms(msg.name, cr.uid, cr.gid)
struct { const char *prefix; unsigned int uid; unsigned int gid; } property_perms[] = { { "net.rmnet0.", AID_RADIO, 0 }, { "net.gprs.", AID_RADIO, 0 }, { "net.ppp", AID_RADIO, 0 }, { "ril.", AID_RADIO, 0 }, { "gsm.", AID_RADIO, 0 }, { "persist.radio", AID_RADIO, 0 }, { "net.dns", AID_RADIO, 0 }, { "net.", AID_SYSTEM, 0 }, { "dev.", AID_SYSTEM, 0 }, { "runtime.", AID_SYSTEM, 0 }, { "hw.", AID_SYSTEM, 0 }, { "sys.", AID_SYSTEM, 0 }, { "service.", AID_SYSTEM, 0 }, { "wlan.", AID_SYSTEM, 0 }, { "dhcp.", AID_SYSTEM, 0 }, { "dhcp.", AID_DHCP, 0 }, { ".", AID_SYSTEM, 0 }, { ".", AID_VPN, 0 }, { "debug.", AID_SHELL, 0 }, { "log.", AID_SHELL, 0 }, { "service.adb.root", AID_SHELL, 0 }, { "persist.sys.", AID_SYSTEM, 0 }, { "persist.service.", AID_SYSTEM, 0 }, { NULL, 0, 0 } }; static int check_perms(const char *name, unsigned int uid, int gid) { int i; if (uid == 0) return 1; if(!strncmp(name, "ro.", 3)) name +=3; for (i = 0; property_perms[i].prefix; i++) { int tmp; if (strncmp(property_perms[i].prefix, name, strlen(property_perms[i].prefix)) == 0) { if ((uid && property_perms[i].uid == uid) || (gid && property_perms[i].gid == gid)) { return 1; } } } return 0; }
从代码中可以看到， 任何不以property_perms[] 中定义的前缀开头的property 是
无法被除root以外的用户访问的，包括system用户。
3. 最后补充Android 的uid gid 定义
#define AID_ROOT 0 /* traditional unix root user */ #define AID_SYSTEM 1000 /* system server */ #define AID_RADIO 1001 /* telephony subsystem, RIL */ #define AID_BLUETOOTH 1002 /* bluetooth subsystem */ #define AID_GRAPHICS 1003 /* graphics devices */ #define AID_INPUT 1004 /* input devices */ #define AID_AUDIO 1005 /* audio devices */ #define AID_CAMERA 1006 /* camera devices */ #define AID_LOG 1007 /* log devices */ #define AID_COMPASS 1008 /* compass device */ #define AID_MOUNT 1009 /* mountd socket */ #define AID_WIFI 1010 /* wifi subsystem */ #define AID_ADB 1011 /* android debug bridge (adbd) */ #define AID_INSTALL 1012 /* group for installing packages */ #define AID_MEDIA 1013 /* mediaserver process */ #define AID_DHCP 1014 /* dhcp client */ #define AID_SDCARD_RW 1015 /* external storage write access */ #define AID_VPN 1016 /* system */ #define AID_KEYSTORE 1017 /* keystore subsystem */ #define AID_SHELL 2000 /* adb and debug shell user */ #define AID_CACHE 2001 /* cache access */ #define AID_DIAG 2002 /* access to diagnostic resources */ /* The 3000 series are intended for use as supplemental group id's only. * They indicate special Android capabilities that the kernel is aware of. */ #define AID_NET_BT_ADMIN 3001 /* bluetooth: create any socket */ #define AID_NET_BT 3002 /* bluetooth: create sco, rfcomm or l2cap sockets */ #define AID_INET 3003 /* can create AF_INET and AF_INET6 sockets */ #define AID_NET_RAW 3004 /* can create raw INET sockets */ #define AID_NET_ADMIN 3005 /* can configure interfaces and routing tables. */ #define AID_MISC 9998 /* access to misc storage */ #define AID_NOBODY 9999 #define AID_APP 10000 /* first app user */
可见root (AID_ROOT = 0) 的权限最高， app (AID_APP = 10000) 权限最低， misc (AID_MISC = 9998) 权限倒数第三低。
所以#1 中描述的目录test3的group 属性设置成了 misc, 则除了 app/nobody 这两个用户，
android系统中其它所有用户都有该目录的group权限！