Date: Mon, 8 Feb 2021 15:00:18 +0530 From: Rohit Keshri <rkeshri@...hat.com> To: oss-security@...ts.openwall.com, alex.gaynor@...il.com Subject: Re: CVE-2021-20226 kernel: use-after-free in io_uring feature Hello, The flaw CVE-2021-20226 is identified as a use-after-free problem with breach to data integrity, confidentiality and system availability, and this may even cause escalated privileges with good troubleshooting skills. I also wanted to add that the affected souce (as was reported for kernel v5.7.0) has been modified from v5.10 kernel version with patch 233295130e53 with following cleanup details. ~~~ $ git show 233295130e53 commit 233295130e53c8dfe6dbef3f52634c3f7e44cd6a Author: Pavel Begunkov <asml.silence@...il.com> Date: Sat Oct 10 18:34:06 2020 +0100 io_uring: clean up ->files grabbing Move work.files grabbing into io_prep_async_work() to all other work resources initialisation. We don't need to keep it separately now, as ->ring_fd/file are gone. It also allows to not grab it when a request is not going to io-wq. .. $ git tag --contains 233295130e53 v5.10 v5.10-rc1 v5.10-rc2 v5.10-rc3 v5.10-rc4 v5.10-rc5 v5.10-rc6 v5.10-rc7 v5.11-rc1 v5.11-rc2 v5.11-rc3 v5.11-rc4 v5.11-rc5 v5.11-rc6 v5.11-rc7 ~~~ Regards, .. Rohit Keshri / Red Hat Product Security Team PGP: OX01BC 858A 07B7 15C8 EF33 BFE2 2EEB 0CBC 84A4 4C2D secalert@...hat.com for urgent response On Mon, Feb 8, 2021 at 2:37 PM Alex Gaynor <alex.gaynor@...il.com> wrote: > Hey, > > Your message says that this is a DoS, however the ZDI page says it's a > priv-esc. Which is right? > > Alex > > On Fri, Feb 5, 2021 at 10:00 AM Rohit Keshri <rkeshri@...hat.com> 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/ > > > > > > Thanks and Regards > > .. > > Rohit Keshri / Red Hat Product Security Team > > PGP: OX01BC 858A 07B7 15C8 EF33 BFE2 2EEB 0CBC 84A4 4C2D > > > > secalert@...hat.com for urgent response > > > > -- > All that is necessary for evil to succeed is for good people to do nothing. > >
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