linux-kernel - Re: [PATCH 08/32] smack: Implement filesystem context security hooks [ver #9]

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Message-ID: <27bf0500-470d-d68a-2757-25cfae05d5a0@schaufler-ca.com>
Date:   Tue, 10 Jul 2018 16:28:30 -0700
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     David Howells <dhowells@...hat.com>
Cc:     viro@...iv.linux.org.uk, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        torvalds@...ux-foundation.org
Subject: Re: [PATCH 08/32] smack: Implement filesystem context security hooks
 [ver #9]

On 7/10/2018 4:19 PM, David Howells wrote:
> Casey Schaufler <casey@...aufler-ca.com> wrote:
>
>>> Implement filesystem context security hooks for the smack LSM.
>>>
>>> Question: Should the ->fs_context_parse_source() hook be implemented to
>>> check the labels on any source devices specified?
>> Checking the label on a block device when doing a mount
>> is just going to end in tears. If you're remounting from
>> an already mounted filesystem it might make sense to check
>> that the new mount doesn't provide greater access than the
>> existing mount. If the original mount has smackfsdefault="_"
>> I could see prohibiting the additional mount having
>> smackfsdefault="*" on a filesystem that doesn't support
>> xattrs. But that requires that a (hopefully) privileged
>> process be involved, and we expect them to have a clue.
>> So no, I don't see it necessary.
> I think I may have meant the device file rather than the actual device
> content.

You may have! I see no reason to look at the label on /dev/sdb1
when mounting it. There's already sufficient privilege required
to protect that in my mind.

>
> David
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