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Date: Fri, 2 Feb 2024 18:19:18 -0500
From: Demi Marie Obenour <demi@...isiblethingslab.com>
To: oss-security@...ts.openwall.com
Subject: Re: Kernel vulnerabilities CVE-2021-33630 &
CVE-2021-33631
On Fri, Feb 02, 2024 at 01:24:58PM -0800, Roxana Bradescu wrote:
>
>
> > On Jan 30, 2024, at 4:56 PM, Demi Marie Obenour <demi@...isiblethingslab.com> wrote:
> >
> > On Tue, Jan 30, 2024 at 03:01:24PM -0800, Greg KH wrote:
> >> On Tue, Jan 30, 2024 at 10:45:00PM +0100, Solar Designer wrote:
> >>> Thank you Greg for looking into these issues. It's great that most
> >>> longterm kernel trees appear already fixed.
> >>
> >> I've taken the one remaining missing fix into the next round of kernel
> >> releases, so all should be good now.
> >>
> >>> For CVE-2021-33631 (the ext4 BUG), both the distro vendor's and NVD's
> >>> CVSS input vectors specify AV:L/AC:L/PR:L/UI:N, which means the
> >>> vulnerability can be triggered by a local system user at will and
> >>> without additional privileges. I'd say that deliberately getting the
> >>> kernel to work on a corrupted filesystem requires at least one of:
> >>> physical access (AV:P) or privileges on the system (PR:H) or user
> >>> interaction (UI:R). However, there's no way to encode this in one CVSS
> >>> vector. Also, in the physical access case, at least the availability
> >>> impact typically does not apply (would be A:N).
> >>
> >> The "interesting" thing here is that the project in question (the
> >> kernel) does not consider "mounting a corrupted filesystem" as a real
> >> attack vector at all. There's been long discussions about it, the most
> >> recent being last year on the kernel summit discuss mailing list, and at
> >> the kernel summit itself.
> >
> > The kernel itself does not, but there are downstreams of the kernel that
> > do for at least a subset of filesystems. These include Android and
> > Chromium OS.
>
> ChromeOS Security here, and this is correct.
Good to know, thanks!
> >> project itself do not. The disconnect is one that drives people who use
> >> sysbot tools to create fancy corrupted filesystem images with the goal
> >> of getting a CVE for their CV, crazy on a weekly basis when the issues
> >> they report get constantly ignored.
> >
> > If someone finds a vulnerability in F2FS or ext4 that can be used to
> > compromise the kernel by crafting a malicious filesystem, they should
> > report it to the Android or Chromium OS security teams, respectively.
> > It’s a verified boot bypass and I expect that it would be in scope for
> > the respective bounty programs. If Android mounts FAT and exFAT in the
> > kernel, then vulnerabilities in these filesystems should be reported to
> > the Android security team.
> >
> > Google requires that F2FS and ext4 are secure against malicious
> > filesystem images, so they should be the ones responsible for fixing any
> > vulnerabilities that require a malicious filesystem image to trigger.
> > Fortunately, they have the resources to do that, so this should not be a
> > problem for them.
>
> Vulnerabilities can be reported to ChromeOS and Android via https://bughunters.google.com
> If any questions, can reach out to chromeos-security@...omium.org
Thank you! I don’t have any to report right now, but I will report any
I do come across.
> > Could this be documented somehow, so that people know to send reports
> > against f2fs and ext4 to those who will actually fix them?
>
> We will document something on the ChromeOS side. Thanks for flagging this!
You’re welcome! Would it be possible for ChromeOS Security to take
responsibility for triaging (and, if the problem is security related,
fixing) ext4 syzbot reports? My understanding is that this would
address the main complaint of the ext4 maintainers, which is work
required to deal with bug reports that are not from end users. The
same applies with f2fs and Android Security.
--
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab
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