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Date: Sun, 11 Jun 2017 20:04:59 -0400
From: Matt Brown <>
To: Mickaël Salaün <>,
 Alan Cox <>
Subject: Re: [PATCH v2 0/1] Add Trusted Path Execution as a stackable LSM

On 06/11/2017 07:30 AM, Mickaël Salaün wrote:
> On 08/06/2017 21:01, Matt Brown wrote:
>> On 6/8/17 2:37 PM, Alan Cox wrote:
>>>> | A trusted path is one that is inside a root owned directory that
>>>> | is not group or world writable.  /bin, /usr/bin, /usr/local/bin, are
>>>> | (under normal circumstances) considered trusted.  Any non-root
>>>> | users home directory is not trusted, nor is /tmp.
>>> Note that in the real world the trusted path would and should also
>>> require that any elements of the path above that point are also locked
>>> down if you are using path based models. Ie you need to ensure nobody has
>>> the ability to rename /usr or /usr/local before you trust /usr/local/bin.
>> So actually in this LSM it's not so much full paths that are trusted,
>> rather it checks that the directory containing the program is only
>> writable by root and that the program itself is only writable by root.
>> For example, consider the following:
>> /user/ with permissions drwxr-xr-x user user
>> /user/user-owned/ with permissions drwxr-xr-x user user
>> /user/user-owned/root-owned/ with permissions drwxr-xr-x root root
>> /user/user-owned/root-owned/exe with permissions -rwxr-xr-x root root
> Some tests would make this scenario clear. ;)
> You can take a look at how seccomp-bpf does with the test_harness.h
> helper. A new kselftest_harness.h will be available soon to not include
> a file from the seccomp-bpf directory (cf. linux-next).

I'll take a look at those. Thanks!


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