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Date: Thu, 7 Mar 2024 14:06:31 -0800
From: Eric Biggers <ebiggers@kernel.org>
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: Andrey Albershteyn <aalbersh@redhat.com>, fsverity@lists.linux.dev,
	linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	chandan.babu@oracle.com
Subject: Re: [PATCH v5 05/24] fs: add FS_XFLAG_VERITY for verity files
Message-ID: <20240307220631.GB1799@sol.localdomain>
References: <20240304191046.157464-2-aalbersh@redhat.com>
 <20240304191046.157464-7-aalbersh@redhat.com>
 <20240304223548.GB17145@sol.localdomain>
 <20240307213911.GQ1927156@frogsfrogsfrogs>
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In-Reply-To: <20240307213911.GQ1927156@frogsfrogsfrogs>

On Thu, Mar 07, 2024 at 01:39:11PM -0800, Darrick J. Wong wrote:
> On Mon, Mar 04, 2024 at 02:35:48PM -0800, Eric Biggers wrote:
> > On Mon, Mar 04, 2024 at 08:10:28PM +0100, Andrey Albershteyn wrote:
> > > @@ -641,6 +645,13 @@ static int fileattr_set_prepare(struct inode *inode,
> > >  	    !(S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode)))
> > >  		return -EINVAL;
> > >  
> > > +	/*
> > > +	 * Verity cannot be set through FS_IOC_FSSETXATTR/FS_IOC_SETFLAGS.
> > > +	 * See FS_IOC_ENABLE_VERITY
> > > +	 */
> > > +	if (fa->fsx_xflags & FS_XFLAG_VERITY)
> > > +		return -EINVAL;
> > 
> > This makes FS_IOC_SETFLAGS and FS_IOC_FSSETXATTR start failing on files that
> > already have verity enabled.
> > 
> > An error should only be returned when the new flags contain verity and the old
> > flags don't.
> 
> What if the old flags have it and the new ones don't?  Is that supposed
> to disable fsverity?  Is removal of the verity information not supported?
> 
> I'm guessing that removal isn't supposed to happen, in which case the
> above check ought to be:
> 
> 	if (!!IS_VERITY(inode) != !!(fa->fsx_xflags & FS_XFLAG_VERITY))
> 		return -EINVAL;
> 
> Right?

Yeah, good catch.  We need to prevent disabling the flag too.  How about:

	if ((fa->flags ^ old_ma->flags) & FS_VERITY_FL)
		return -EINVAL;

That would be consistent with how changes to other flags such as FS_APPEND_FL
and FS_IMMUTABLE_FL are detected earlier in the function.

- Eric