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Date: Fri, 7 Jul 2023 23:46:18 +0200
From: Solar Designer <solar@...nwall.com>
To: oss-security@...ts.openwall.com
Cc: Ruihan Li <lrh2000@....edu.cn>
Subject: Re: StackRot (CVE-2023-3269): Linux kernel privilege escalation vulnerability
On Wed, Jul 05, 2023 at 08:12:01PM +0800, Ruihan Li wrote:
> I reported this vulnerability to the Linux kernel security team on June 15th.
> Following that, the process of addressing this bug was led by Linus Torvalds.
> Given its complexity, it took nearly two weeks to develop a set of patches that
> received consensus.
>
> On June 28th, during the merge window for Linux kernel 5.5, the fix was merged
> into Linus' tree. Linus provided a [comprehensive merge message][fix] to
> elucidate the patch series from a technical perspective.
>
> [fix]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9471f1f2f50282b9e8f59198ec6bb738b4ccc009
>
> These patches were subsequently backported to stable kernels ([6.1.37][6.1],
> [6.3.11][6.3], and [6.4.1][6.4]), effectively resolving the "Stack Rot" bug on
> July 1st.
>
> [6.1]: https://lore.kernel.org/stable/2023070133-create-stainless-9a8c@gregkh/T/
> [6.3]: https://lore.kernel.org/stable/2023070146-endearing-bounding-d21a@gregkh/T/
> [6.4]: https://lore.kernel.org/stable/2023070140-eldercare-landlord-133c@gregkh/T/
Thank you very much Ruihan Li! This is impressive work both by you and
by the kernel maintainers.
For the oss-security community, I need to acknowledge and explain that
we made a rare exception from the linux-distros policy on 14 days
maximum embargo time, and why we did that. We also made use of the
exception pre-granted for "Linux kernel issues concurrently or very
recently handled by the Linux kernel security team", where a "silent"
fix is possible without us treating that as embargo end.
Ruihan Li brought the issue to linux-distros at the same time with
contacting the Linux kernel security team on June 15th. This meant the
latest date for public disclosure would be June 29th. As it happened,
this issue was genuinely taking almost the full 14 days to fix,
including patch review, testing on multiple platforms, and adjustments
to the initial fixes. The fix seemed ready on June 28th, and making the
information fully public on the 29th was within consideration. However,
we decided to allocate an extra 6 days beyond the usual maximum of 14,
until July 5th. The intent was for the "silent" fix (committed by Linus
on June 28th) to propagate to stable kernels, to prepared distro updates
(not to be released with the fix documented until July 5th), and for it
to stabilize in case more issues are found and addressed in this period
(which wasn't unlikely given the complexity).
Many of the distros present on linux-distros only used kernels older
than 6.1, so were not affected. This meant two things: on one hand, few
distros would benefit from the delay, but on the other also few would
possibly be hurt by the delay. For many, this just did not matter.
I didn't keep track, but apparently there were first compile-time and
then runtime issues with the fix on sparc32, parisc, ia64, as addressed
in this thread:
https://lore.kernel.org/all/CA+G9fYsM2s3q1k=+wHszvNbkKbHGe1pskkffWvaGXjYrp6qR=g@mail.gmail.com/#t
Linus also promptly found (and informed linux-distros on June 29th) that
a runtime warning message temporarily introduced along with the fix (but
with a separate commit) was getting triggered too commonly. This is
finally fixed in:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=6cd06ab12d1afdab3847e7981f301bd0404aaa5c
I'm not currently aware of any other issues found and addressed during
the extra 6 days, so I'm not sure whether this delay was of sufficient
benefit. However, we didn't know in advance - it could well have been.
> ## Exploit
>
> **The complete exploit code and a comprehensive write-up will be made publicly
> available no later than the end of July.**
The complete exploit code wasn't posted to linux-distros, so it is not
subject to the policy on maximum of 7 days between vulnerability
disclosure on oss-security and posting of the exploit to oss-security.
Some details on triggering the bug were on linux-distros. Normally,
they would be subject to the policy and so brought to oss-security no
later than July 12th, which Ruihan Li did not object to doing, but
expressed a preference to post the complete exploit by the end of July
instead. I agreed to make this exception.
Thanks,
Alexander
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