linux-kernel - Re: [RFC PATCH v14 15/19] fsverity: consume builtin signature via LSM hook

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Message-ID: <568fae5e-a6d4-4832-a1a1-ac3f4f93d650@schaufler-ca.com>
Date: Tue, 12 Mar 2024 11:51:20 -0700
From: Casey Schaufler <casey@...aufler-ca.com>
To: Fan Wu <wufan@...ux.microsoft.com>, Eric Biggers <ebiggers@...nel.org>
Cc: corbet@....net, zohar@...ux.ibm.com, jmorris@...ei.org, serge@...lyn.com,
 tytso@....edu, axboe@...nel.dk, agk@...hat.com, snitzer@...nel.org,
 eparis@...hat.com, paul@...l-moore.com, linux-doc@...r.kernel.org,
 linux-integrity@...r.kernel.org, linux-security-module@...r.kernel.org,
 linux-fscrypt@...r.kernel.org, linux-block@...r.kernel.org,
 dm-devel@...ts.linux.dev, audit@...r.kernel.org,
 linux-kernel@...r.kernel.org, Deven Bowers
 <deven.desai@...ux.microsoft.com>, Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [RFC PATCH v14 15/19] fsverity: consume builtin signature via LSM
 hook

On 3/12/2024 11:14 AM, Fan Wu wrote:
>
>
> On 3/11/2024 8:07 PM, Eric Biggers wrote:
>> On Mon, Mar 11, 2024 at 07:57:12PM -0700, Eric Biggers wrote:
>>>
>>> As I've said before, this commit message needs some work.  It
>>> currently doesn't
>>> say anything about what the patch actually does.
>>>
>>> BTW, please make sure you're Cc'ing the fsverity mailing list
>>> (fsverity@...ts.linux.dev), not fscrypt
>>> (linux-fscrypt@...r.kernel.org).
>>
>> Also, I thought this patch was using a new LSM hook, but I now see
>> that you're
>> actually abusing the existing security_inode_setsecurity() LSM hook. 
>> Currently
>> that hook is called when an xattr is set.  I don't see any precedent for
>> overloading it for other purposes.  This seems problematic, as it
>> means that a
>> request to set an xattr with the name you chose
>> ("fsverity.builtin-sig") will be
>> interpreted by LSMs as the fsverity builtin signature.  A dedicated
>> LSM hook may
>> be necessary to avoid issues with overloading the existing xattr hook
>> like this.
>>
>> - Eric
>
> Thanks for the suggestion. I found that using
> security_inode_setsecurity() causes issues with SMACK's
> inode_setsecurity() hook. I will crate a dedicated new hook like
> security_inode_setsig() in the next version.

What is the issue you encountered with the Smack hook?

>
> -Fan
>