Android Permission

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转载最新推荐文章于 2026-05-27 00:15:21 发布 1.2k 阅读 AI 写同款· GEO 优化 ›

Android权限与Permission机制 Android 是一个权限分离的系统。利用 Linux 已有的权限管理机制，通过为每一个 Application 分配不同的 uid 和 gid ，从而使得不同的 Application 之间的私有数据和访问达到隔离的目的。阅读详情

http://blog.youkuaiyun.com/stevenliyong/archive/2010/03/03/5343085.aspx

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 <path> [mode] [owner] [group] */ if (nargs >= 3) { mode = strtoul(args[2], 0, 8); } if (mkdir(args[1], mode)) { return -errno; } if (nargs >= 4) { uid_t uid = decode_uid(args[3]); gid_t gid = -1; if (nargs == 5) { gid = decode_uid(args[4]); } if (chown(args[1], uid, gid)) { return -errno; } } return 0; }

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

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 },
    { "vpn.",             AID_SYSTEM,   0 },
    { "vpn.",             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 /* vpn 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！

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