访问 `proc` 文件系统以从系统应用程序读取 `/proc/[pid]/some-file` [英] Accessing `proc` file-system to read `/proc/[pid]/some-file` from a system app

问题描述

我有一个自定义 A10 存储库，我试图在其中创建一个能够读取 /proc/[pid]/some-file 文件的应用程序，例如stat 和 status，有点像 ps 的作用.

I have a custom A10 repo in which I'm trying to create an app that would be able to read /proc/[pid]/some-file files e.g. stat and status, kind of like ps does.

阅读此 answer 后，很明显应该添加一个 AID_READPROC已完成使用自定义权限.

Having read this answer it was clear that a AID_READPROC should be added which I have done using a custom permission.

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.poke.mon"
    android:sharedUserId="android.uid.system">
<!-- More stuff -->
         <uses-permission android:name="com.poke.READPROC_PERM" />
<!-- More stuff -->
  </application>
</manifest>

我通过编辑适当的 platform.xml、AndroidManifest.xml 和 sytem-current 添加了 com.poke.READPROC_PERM.txt 文件并在 privapp-permissions 文件中允许该权限

I have added com.poke.READPROC_PERM by editing the appropriate platform.xml, AndroidManifest.xml and sytem-current.txt files and allowing that permission in the privapp-permissions file

我已经通过 cat 验证了我的应用进程的 status 文件，并验证了 gid 3009 确实存在.

I have validated by cat-ing the status file for my app's process and verifying that gid 3009 is indeed present.

但是我仍然被 sepolicy 阻止(禁用强制执行，代码可以访问文件).

However I was still being blocked by sepolicy (with the enforcement disabled the code could access the files).

将 r_dir_file(priv_app, proc) 添加到 priv_app.te 导致错误.

Adding r_dir_file(priv_app, proc) to the priv_app.te resulted in errors.

编译器给出的原因是这个行在 coredomain.te 中:

The reason given by the compiler was this line in coredomain.te :

# Core domains are not permitted to use kernel interfaces which are not
# explicitly labeled.
# TODO(b/65643247): Apply these neverallow rules to all coredomain.
full_treble_only(`
  # /proc
  neverallow {
    coredomain
    -init
    -vold
  } proc:file no_rw_file_perms;

创建自定义域导致了我可能想要的类似错误

Creating a custom domain resulted in similar errors as I probably want to

typeattribute my_apps_domain coredomain;

为了避免大量的复杂性和重复(我需要与其他服务等进行通信).

To avoid a lot of complexity and duplication (I need to communicate with other services etc.).

有没有办法解决这个限制?(例如，查看 genfscon 它似乎不支持通配符映射，例如 /proc/\d+/some-file)

Is there a way to work around that limitation? (e.g. looking at genfscon it doesn't seem to support wildchar mapping e.g. /proc/\d+/some-file)

shell 能够很好地执行 ps 似乎也很奇怪，但它也是 第一行shell.te:

It also seems weird that shell is able to do ps just fine yet it's also coredomain defined by the first line of shell.te:

typeattribute shell coredomain;

那么也许我还缺少其他一些神奇的 sepolicy 门?

So maybe there's some other magical sepolicy door I'm missing?

推荐答案

1. 为您的应用定义自定义域:

1. Define an custom domain for your app：

user=_app isPrivApp=true seinfo=platform name=com.myapp.packagename domain=my_custom_domain type=app_data_file levelFrom=all

user=_app isPrivApp=true seinfo=platform name=com.myapp.packagename domain=my_custom_domain type=app_data_file levelFrom=all

ref:https://cs.android.com/android/platform/superproject/+/master:device/google/coral-sepolicy/private/seapp_contexts;drc=01b96a3a966f075abcba27cb415cece348a3278e>l=5

ref:https://cs.android.com/android/platform/superproject/+/master:device/google/coral-sepolicy/private/seapp_contexts;drc=01b96a3a966f075abcba27cb415cece348a3278e;l=5

1. 将自定义域标记为核心域:

1. Label the custom domain as coredomain:

typeattribute my_custom_domain coredomain;

typeattribute my_custom_domain coredomain;

然后您将使用 neverallow 限制.

Then you will work with the neverallow limit.

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