From: Eric Biggers <ebiggers@kernel.org>
To: Dave Chinner <david@fromorbit.com>
Cc: "Darrick J. Wong" <djwong@kernel.org>,
Bagas Sanjaya <bagasdotme@gmail.com>,
Pengfei Xu <pengfei.xu@intel.com>,
linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
heng.su@intel.com, dchinner@redhat.com, lkp@intel.com,
Linux Regressions <regressions@lists.linux.dev>
Subject: Re: [Syzkaller & bisect] There is BUG: unable to handle kernel NULL pointer dereference in xfs_extent_free_diff_items in v6.4-rc3
Date: Tue, 23 May 2023 23:46:12 +0000 [thread overview]
Message-ID: <20230523234612.GG888341@google.com> (raw)
In-Reply-To: <ZG07WoKnBzaN4T1L@dread.disaster.area>
On Wed, May 24, 2023 at 08:16:58AM +1000, Dave Chinner wrote:
> config XFS_SUPPORT_V4
> bool "Support deprecated V4 (crc=0) format"
> depends on XFS_FS
> default y
> help
> The V4 filesystem format lacks certain features that are supported
> by the V5 format, such as metadata checksumming, strengthened
> metadata verification, and the ability to store timestamps past the
> year 2038. Because of this, the V4 format is deprecated. All users
> should upgrade by backing up their files, reformatting, and restoring
> from the backup.
>
> Administrators and users can detect a V4 filesystem by running
> xfs_info against a filesystem mountpoint and checking for a string
> beginning with "crc=". If the string "crc=0" is found, the
> filesystem is a V4 filesystem. If no such string is found, please
> upgrade xfsprogs to the latest version and try again.
>
> This option will become default N in September 2025. Support for the
> V4 format will be removed entirely in September 2030. Distributors
> can say N here to withdraw support earlier.
>
> To continue supporting the old V4 format (crc=0), say Y.
> To close off an attack surface, say N.
>
> This was added almost 3 years ago in mid-2020. We're more than half
> way through the deprecation period and then we're going to turn off
> v4 support by default. At this point, nobody should be using v4
> filesystems in new production systems, and those that are should be
> preparing for upstream and distro support to be withdraw in the next
> couple of years...
Great to see that this exists now and there is a specific deprecation plan!
> > Then you could just tell the people fuzzing XFS filesystem images
> > that they need to use that option. That would save everyone a lot of time.
> > (To be clear, I'm not arguing for the XFS policy on v4 filesystems being right
> > or wrong; that's really not something I'd like to get into again... I'm just
> > saying that if that's indeed your policy, this is what you should do.)
>
> It should be obvious by now that we've already done this. 3 years
> ago, in fact. And yet we are still having the same problems. Maybe
> this helps you understand the level of frustration we have with all
> the people running fuzzing bots out there....
I don't see evidence that this actually happened, though perhaps we are not
looking in the same places. https://lore.kernel.org/all/?q=XFS_SUPPORT_V4
brings up little except the original patch thread, nor did
https://github.com/search?q=XFS_SUPPORT_V4&type=issues find anything.
Anyway, I took 3 minutes to file an issue in the syzkaller repo
(https://github.com/google/syzkaller/issues/3918), so at least this should get
resolved for syzbot soon.
- Eric
prev parent reply other threads:[~2023-05-23 23:46 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-22 2:07 [Syzkaller & bisect] There is BUG: unable to handle kernel NULL pointer dereference in xfs_extent_free_diff_items in v6.4-rc3 Pengfei Xu
2023-05-22 6:39 ` Bagas Sanjaya
2023-05-22 16:05 ` Darrick J. Wong
2023-05-22 17:05 ` Linux regression tracking (Thorsten Leemhuis)
2023-05-23 6:08 ` Bagas Sanjaya
2023-05-23 6:44 ` Pengfei Xu
2023-05-23 0:00 ` Eric Biggers
2023-05-23 7:31 ` Dave Chinner
2023-05-23 9:14 ` Pengfei Xu
2023-05-23 21:52 ` Dave Chinner
2023-05-24 2:20 ` Pengfei Xu
2023-05-23 16:50 ` Eric Biggers
2023-05-23 22:16 ` Dave Chinner
2023-05-23 23:46 ` Eric Biggers [this message]
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