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Date: Fri, 5 Feb 2021 17:47:01 +0100
From: Salvatore Bonaccorso <>
Subject: Re: CVE-2021-20226 kernel: use-after-free in io_uring


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:

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.

Is the fix included thus in the merge from

Many thanks in advance!


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