Re: [PATCH 1/3] xfs: kill the XFS_IOC_{ALLOC,FREE}SP* ioctls

[Dave Chinner <david@fromorbit.com>]

On Tue, Jan 11, 2022 at 03:22:46PM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> According to the glibc compat header for Irix 4, these ioctls originated
> in April 1991 as a (somewhat clunky) way to preallocate space at the end
> of a file on an EFS filesystem.  XFS, which was released in Irix 5.3 in
> December 1993, picked up these ioctls to maintain compatibility and they
> were ported to Linux in the early 2000s.
> 
> Recently it was pointed out to me they still lurk in the kernel, even
> though the Linux fallocate syscall supplanted the functionality a long
> time ago.  fstests doesn't seem to include any real functional or stress
> tests for these ioctls, which means that the code quality is ... very
> questionable.  Most notably, it was a stale disk block exposure vector
> for 21 years and nobody noticed or complained.  As mature programmers
> say, "If you're not testing it, it's broken."
> 
> Given all that, let's withdraw these ioctls from the XFS userspace API.
> Normally we'd set a long deprecation process, but I estimate that there
> aren't any real users, so let's trigger a warning in dmesg and return
> -ENOTTY.
> 
> See: CVE-2021-4155
> 
> Augments: 983d8e60f508 ("xfs: map unwritten blocks in XFS_IOC_{ALLOC,FREE}SP just like fallocate")
> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> Reviewed-by: Eric Sandeen <sandeen@redhat.com>

Looks good now.

Reviewed-by: Dave Chinner <dchinner@redhat.com>
-- 
Dave Chinner
david@fromorbit.com