Date: Mon, 8 Aug 2022 12:00:42 +0200 From: Solar Designer <solar@...nwall.com> To: David Hildenbrand <david@...hat.com> Cc: oss-security@...ts.openwall.com Subject: Re: CVE-2022-2590: Linux kernel: Modifying shmem/tmpfs files without write permissions On Mon, Aug 08, 2022 at 09:18:27AM +0200, David Hildenbrand wrote: > 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. Thanks, David! Apparently, your proposed fix for Linux >= v5.19 is this, as you posted to linux-kernel and linux-mm: [PATCH v1] mm/gup: fix FOLL_FORCE COW security issue and remove FOLL_COW https://lists.openwall.net/linux-kernel/2022/08/08/418 https://firstname.lastname@example.org/ (two links to the same message) > I have a working reproducer that I will post as reply to this mail in > one week (August 15). Alexander
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