Android Permission

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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;
}
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

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;
}
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 },
    { "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;
}
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 */
#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！

本文来自CSDN博客，转载请标明出处：http://blog.csdn.net/stevenliyong/archive/2010/03/03/5343085.aspxs