Date: Mon, 8 Aug 2022 09:18:27 +0200 From: David Hildenbrand <david@...hat.com> To: oss-security@...ts.openwall.com Subject: CVE-2022-2590: Linux kernel: Modifying shmem/tmpfs files without write permissions 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). -- Thanks, David / dhildenb
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