How Android obtains access to a kernel node in SELinux "Go"

This article was reproduced from: http://blog.csdn.net/u012719256/article/details/52585956

Android 5.0, because of the seandroid/selinux security mechanism, even if you have root privileges, or a kernel node set to 777 of the permissions, still cannot be accessed at the JNI layer.

This article will use a user-defined kernel node /dev/wf_bt As an example, hands-on teaches the reader how to gain access to the node in the JNI layer. The first step: find the process that needs to access the kernel node, the author own this node by System_serverProcess to access the second step: Open File androidl/android/external/sepolicy/ file_contexts.beFollow the notation in this file to define the name you want for your node: [Python]View Plaincopy

1. /dev/tegra.* U:object_r:video_device:s0
2. /dev/tf_driver U:object_r:tee_device:s0
3. /dev/tty U:object_r:owntty_device:s0
4. /dev/tty[0-9]* u:object_r:tty_device:s0
5. # We Add here
6. /DEV/WF_BT U:object_r:wf_bt_device:s0

Wf_bt_device is custom, and the other left and right sides of the content are consistent with the example above. Step three: Open File androidl/android/external/sepolicy/ Device.teFollowing the writing in this document, the second step of the Wf_bt_device is declared as Dev_type: [Python]View Plaincopy

1. # Device Types
2. Type device, Dev_type, Fs_type;
3. Type Alarm_device, Dev_type, Mlstrustedobject;
4. Type Adb_device, Dev_type;
5. Type Ashmem_device, Dev_type, Mlstrustedobject;
6. Type Audio_device, Dev_type;
7. Type Binder_device, Dev_type, Mlstrustedobject;
8. Type Block_device, Dev_type;
9. # We Add here
10. type Wf_bt_device, Dev_type;

Fourth step: Under the androidl/android/external/sepolicy/directory many. te files end with a process name, for example, there are surfaceflinger for the surfaceflinger process, there are vold.te for the vold process, just from the first step, this node is accessed by the System_server process, so we found System_server. Te opens to allow this process to read and write access to the/DEV/WF_BT. [Python]View Plaincopy

1. # Read/write To/proc/net/xt_qtaguid/ctrl and And/dev/xt_qtaguid.
2. Allow System_server qtaguid_proc:file rw_file_perms;
3. Allow System_server qtaguid_device:chr_file rw_file_perms;
5. # Chr_file indicates the character device file, if it is a normal file, directory please use Dir
6. # rw_file_perms represents read and Write permissions
7. Allow system_server wf_bt_device:chr_file rw_file_perms; Allows the system_server process to have read and write access to the Wf_bt_device character device;

This means that the system_server process is allowed to have read and write access to the Wf_bt_device character device. After you change this, you can make installclean;make-j16 compile the image to verify that the permissions are successful. FD =open ("/dev/wf_bt", O_rdonly | O_noctty); ABSOLUTE SUCCESS!!!!!

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Allow system_server wf_bt_device:chr_file rw_file_perms;Allows the system_server process to have read and write access to this character device for Wf_bt_device.

How Android obtains access to a kernel node in SELinux "Go"