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

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Date:   Mon, 8 Apr 2019 09:20:47 +0300
From:   Amir Goldstein <amir73il@...il.com>
To:     "Darrick J. Wong" <darrick.wong@...cle.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 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

Thanks,
Amir.