linux-ext4 - Re: [PATCH 4/4] xfs: don't allow most setxattr to immutable files

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Message-ID: <20190409031801.GD5147@magnolia>
Date:   Mon, 8 Apr 2019 20:18:01 -0700
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Amir Goldstein <amir73il@...il.com>
Cc:     Dave Chinner <david@...morbit.com>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Ext4 <linux-ext4@...r.kernel.org>,
        Linux Btrfs <linux-btrfs@...r.kernel.org>
Subject: Re: [PATCH 4/4] xfs: don't allow most setxattr to immutable files

On Mon, Apr 08, 2019 at 09:20:47AM +0300, Amir Goldstein wrote:
> On Sun, Apr 7, 2019 at 11:28 PM Darrick J. Wong <darrick.wong@...cle.com> wrote:
> >
> > From: Darrick J. Wong <darrick.wong@...cle.com>
> >
> > The chattr manpage has this to say about immutable files:
> >
> > "A file with the 'i' attribute cannot be modified: it cannot be deleted
> > or renamed, no link can be created to this file, most of the file's
> > metadata can not be modified, and the file can not be opened in write
> > mode."
> >
> > However, we don't actually check the immutable flag in the setattr code,
> > which means that we can update project ids and extent size hints on
> > supposedly immutable files.  Therefore, reject a setattr call on an
> > immutable file except for the case where we're trying to unset
> > IMMUTABLE.
> >
> > Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
> 
> Did you miss my comment on v1, or do you not think this use case
> is going to hurt any application that is not a rootkit?
> 
> chattr +i foo => OK
> chattr +i foo => -EPERM

Nah, I plain forgot to update the patch. :(

Will send v2 where you're allowed to +i multiple times so long as that's
the only thing you're changing.

--D

> Thanks,
> Amir.