linux-ext4 - Re: [PATCH 3/3] xfs: don't allow most setxattr to immutable files

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Date:   Fri, 29 Mar 2019 08:29:48 +1100
From:   Dave Chinner <david@...morbit.com>
To:     "Darrick J. Wong" <darrick.wong@...cle.com>
Cc:     linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-btrfs@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 3/3] xfs: don't allow most setxattr to immutable files

On Thu, Mar 28, 2019 at 10:50:54AM -0700, Darrick J. Wong 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>
> ---
>  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 2bd1c5ab5008..9cf0bc0ae2bd 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1067,6 +1067,14 @@ 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)

Looks fine - catches both FS_IOC_SETFLAGS and FS_IOC_FSSETXATTR
for XFS.

Do the other filesystems that implement FS_IOC_FSSETXATTR have
the same bug?

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com