Hey there, let's work through this SELinux policy compilation error you're hitting. The issue is straightforward: SELinux doesn't recognize the xyz_block_device type because you haven't defined it yet, or mapped it to your actual block device. Here's how to fix it step by step:

Step 1: Define the SELinux Type #

First, you need to declare the xyz_block_device type in a relevant TE file. For system-level block devices, the standard spot is system/sepolicy/private/device.te. Add this line:

type xyz_block_device, dev_type;

The dev_type attribute tags this as a generic device type, which is required for block devices in SELinux.

Step 2: Map the Block Device Path to the Type #

Next, you have to tell SELinux which physical block device node corresponds to this new type. Edit system/sepolicy/public/file_contexts (or the vendor-specific file_contexts if your device lives in the vendor partition) and add a rule like this:

/dev/xyz    u:object_r:xyz_block_device:s0

Replace /dev/xyz with the real path of your block device (for example, /dev/block/xyz if it resides in the block subdirectory). This line links the device node's filesystem path to the xyz_block_device security context.

Step 3: Re-add Your Permission Rule #

Now head back to system/sepolicy/private/untrusted_app.te and re-include your original permission rule:

allow untrusted_app xyz_block_device:blk_file { read write };

SELinux will now recognize the xyz_block_device type, and your compilation should complete without errors.

Quick Tips #

• If your block device is part of the vendor partition (common for OEM-specific hardware), put the type definition and file context rule in your vendor's sepolicy directory (e.g., vendor/your_oem/sepolicy/) instead of the system directory—this follows Android's partition isolation best practices.
• Double-check that the device path in file_contexts exactly matches where your block device is created at runtime. A mismatch here will lead to SELinux denials even after compilation succeeds.

内容的提问来源于stack exchange，提问作者Palak