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Date: Fri, 5 Feb 2021 17:47:01 +0100
From: Salvatore Bonaccorso <carnil@...ian.org>
To: oss-security@...ts.openwall.com
Subject: Re: CVE-2021-20226 kernel: use-after-free in io_uring
feature
Hi,
On Fri, Feb 05, 2021 at 08:27:57PM +0530, Rohit Keshri wrote:
> Hello Team,
>
> A use-after-free flaw was found in the io_uring in Linux kernel, where a
> local attacker with a user privilege could cause a denial of service
> problem on the system
>
> The issue results from the lack of validating the existence of an object
> prior to performing operations on the object by not incrementing the file
> reference counter while in use.
>
> The highest threat from this vulnerability is to data integrity,
> confidentiality and system availability.
>
>
> 'CVE-2021-20226' was assigned by Red Hat.
>
> This issue was reported by Ryota Shiga of Flatt Security Team.
>
>
> Reference:
>
> https://www.zerodayinitiative.com/advisories/ZDI-21-001/
Can you point to the upstream fixes for this issue? The above
reference claims it to be fixed in 5.10.2 (but I guess this is just
the version where it was re-verified to be fixed). The timeline would
indicate that the issue would be fixed earlier (and there seem to be
no io_uring changes between 5.10.1 and 5.10.2).
It was reported on 2020-07-17 to the vendor, as the maximum embargo
time would be 7 days if this was via security@k.o does this means that
it was possibly fixed somehwere already around the 5.9-rc1 release?
The Red Hat report has a bit more details:
A use-after-free flaw was found in io_grab_files in fs/io_uring.c in
io_uring I/O access. This flaw could allow a local attacker with a
user privilege to crash the system at device IORING_OP_CLOSE operation
where a file reference counter was not incremented while in use. This
vulnerability could even lead to a kernel information leak problem.
https://bugzilla.redhat.com/show_bug.cgi?id=1873476
Is the fix included thus in the merge from
https://git.kernel.org/linus/cdc8fcb49905c0b67e355e027cb462ee168ffaa3
(v5.9-rc1)?
Many thanks in advance!
Regards,
Salvatore
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