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 firstname.lastname@example.org 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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