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

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Date: Tue, 12 Mar 2024 11:14:26 -0700
From: Fan Wu <wufan@...ux.microsoft.com>
To: 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>
Subject: Re: [RFC PATCH v14 15/19] fsverity: consume builtin signature via LSM
 hook



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.

-Fan