Subject: Re: [PATCH 4/4] xfs: don't allow most setxattr to immutable files
To:     "Darrick J. Wong" <darrick.wong@oracle.com>
Cc:     david@fromorbit.com, linux-xfs@vger.kernel.org, linux-mm@kvack.org,
        linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org,
        linux-btrfs@vger.kernel.org
References: <155466882175.633834.15261194784129614735.stgit@magnolia>
 <155466884962.633834.14320700092446721044.stgit@magnolia>
From:   Allison Henderson <allison.henderson@oracle.com>
Message-ID: <4b6985a9-a386-90e9-63b4-b906d2cb216a@oracle.com>
Date:   Sun, 7 Apr 2019 22:57:05 -0700
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Looks ok:
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>

On 4/7/19 1:27 PM, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.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@oracle.com>
> ---
>   fs/xfs/xfs_ioctl.c |    8 ++++++++
>   1 file changed, 8 insertions(+)
> 
> 
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index 5a1b96dad901..1215713d7814 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1061,6 +1061,14 @@ xfs_ioctl_setattr_xflags(
>   	    !capable(CAP_LINUX_IMMUTABLE))
>   		return -EPERM;
>   
> +	/*
> +	 * If immutable is set and we are not clearing it, we're not allowed
> +	 * to change anything else in the inode.
> +	 */
> +	if ((ip->i_d.di_flags & XFS_DIFLAG_IMMUTABLE) &&
> +	    (fa->fsx_xflags & FS_XFLAG_IMMUTABLE))
> +		return -EPERM;
> +
>   	/* diflags2 only valid for v3 inodes. */
>   	di_flags2 = xfs_flags2diflags2(ip, fa->fsx_xflags);
>   	if (di_flags2 && ip->i_d.di_version < 3)
>