在Android selinux中转义冒号字符

Question

I'm trying to create a custom selinux policy for my AOSP build wherein untrusted apps can write to /sys/class/leds/led:flash_torch/brightness thereby controlling the flashlight.

To do this, I edited the following files in external/sepolicy

domain.te

allow domain sys_flashlight:file rw_file_perms;

file.te

type sys_flashlight, fs_type;

untrusted_app.te

allow untrusted_app sys_flashlight:file rw_file_perms;

Now, the final piece of the puzzle is the file genfs_contexts . Ideally, I would want to change this file to contain something like:

genfscon proc /sys/class/leds/led:flash_torch/brightness u:object_r:sys_flashlight:s0

First, bear in mind that the above statement is wrong . genfscon proc is meant to only be used with procfs . Ignoring that, Since the file path contains the : character, the build process complains by stating:

external/sepolicy/genfs_contexts:11:ERROR 'syntax error' at token ':' on line 12972:
genfscon proc /sys/class/leds/led:flash_torch/brightness u:object_r:sysfs_flashlight:s0
genfscon proc /foreground u:object_r:proc_foreground:s0
checkpolicy:  error(s) encountered while parsing configuration
make: *** [out/target/product/hammerhead/obj/ETC/sepolicy_intermediates/sepolicy] Error 1
make: *** Waiting for unfinished jobs....

How can I escape the : character while writing the selinux policies?

edit : I've already tried quoting the path and using \\ to try and escape the : with no luck

Answer 1

Looking at the parser statements for checkpolicy:

policy_parse.y:139:%token GENFSCON
policy_parse.y:750:genfs_context_def    : GENFSCON filesystem path '-' identifier security_context_def
policy_parse.y:752:         | GENFSCON filesystem path '-' '-' {insert_id("-", 0);} security_context_def
policy_parse.y:754:                        | GENFSCON filesystem path 

We see GENFSCON's path token is what is expanding, which is defined as:

policy_scan.l:252:"/"({alnum}|[_\.\-/])*            { return(PATH); }

Thus : is not valid in the set.

This seems like a bug that the character set does not include these.