Date: Mon, 15 Aug 2022 08:59:02 +0200 From: David Hildenbrand <david@...hat.com> To: oss-security@...ts.openwall.com Cc: "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>, Greg KH <gregkh@...uxfoundation.org>, Nadav Amit <namit@...are.com> Subject: Re: CVE-2022-2590: Linux kernel: Modifying shmem/tmpfs files without write permissions On 08.08.22 09:18, David Hildenbrand wrote: > Hi, > > I found a security issue (CVE-2022-2590) in the Linux kernel similar to > Dirty COW (CVE-2016-5195), however, restricted to shared memory (shmem / > tmpfs). I notified distributions one week ago and the embargo ended today. > > An unprivileged user can modify file content of a shmem (tmpfs) file, > even if that user does not have write permissions to the file. The file > could be an executable. > > The introducing upstream commit ID is: > 9ae0f87d009c ("mm/shmem: unconditionally set pte dirty in > mfill_atomic_install_pte") > > Linux >= v5.16 is affected on x86-64 and aarch64 if the kernel is > compiled with CONFIG_USERFAULTFD=y. For Linux < v5.19 it's sufficient to > revert the problematic commit, which is possible with minor contextual > conflicts. For Linux >= v5.19 I'll send a proposal fix today. > > I have a working reproducer that I will post as reply to this mail in > one week (August 15). > Hi, attached is the reproducer. When run without arguments, it will test with a memfd that is sealed for writes. upstream, 5.18-stable and 5.19-stable are still to be fixed. The fix is on its way upstream and us already in -next, so I suppose it should all be fixed fairly soonish. -- Thanks, David / dhildenb View attachment "reproducer.c" of type "text/x-csrc" (7506 bytes)
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