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Message-ID: <2024110936-CVE-2024-50250-eb8a@gregkh> Date: Sat, 9 Nov 2024 11:15:58 +0100 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-cve-announce@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org> Subject: CVE-2024-50250: fsdax: dax_unshare_iter needs to copy entire blocks Description =========== In the Linux kernel, the following vulnerability has been resolved: fsdax: dax_unshare_iter needs to copy entire blocks The code that copies data from srcmap to iomap in dax_unshare_iter is very very broken, which bfoster's recent fsx changes have exposed. If the pos and len passed to dax_file_unshare are not aligned to an fsblock boundary, the iter pos and length in the _iter function will reflect this unalignment. dax_iomap_direct_access always returns a pointer to the start of the kmapped fsdax page, even if its pos argument is in the middle of that page. This is catastrophic for data integrity when iter->pos is not aligned to a page, because daddr/saddr do not point to the same byte in the file as iter->pos. Hence we corrupt user data by copying it to the wrong place. If iter->pos + iomap_length() in the _iter function not aligned to a page, then we fail to copy a full block, and only partially populate the destination block. This is catastrophic for data confidentiality because we expose stale pmem contents. Fix both of these issues by aligning copy_pos/copy_len to a page boundary (remember, this is fsdax so 1 fsblock == 1 base page) so that we always copy full blocks. We're not done yet -- there's no call to invalidate_inode_pages2_range, so programs that have the file range mmap'd will continue accessing the old memory mapping after the file metadata updates have completed. Be careful with the return value -- if the unshare succeeds, we still need to return the number of bytes that the iomap iter thinks we're operating on. The Linux kernel CVE team has assigned CVE-2024-50250 to this issue. Affected and fixed versions =========================== Issue introduced in 6.1.113 with commit 1bec6782a25c and fixed in 6.1.116 with commit bdbc96c23197 Issue introduced in 6.2 with commit d984648e428b and fixed in 6.6.60 with commit 9bc18bb476e5 Issue introduced in 6.2 with commit d984648e428b and fixed in 6.11.7 with commit 8e9c0f500b42 Issue introduced in 6.2 with commit d984648e428b and fixed in 6.12-rc6 with commit 50793801fc7f Please see https://www.kernel.org for a full list of currently supported kernel versions by the kernel community. Unaffected versions might change over time as fixes are backported to older supported kernel versions. The official CVE entry at https://cve.org/CVERecord/?id=CVE-2024-50250 will be updated if fixes are backported, please check that for the most up to date information about this issue. Affected files ============== The file(s) affected by this issue are: fs/dax.c Mitigation ========== The Linux kernel CVE team recommends that you update to the latest stable kernel version for this, and many other bugfixes. Individual changes are never tested alone, but rather are part of a larger kernel release. Cherry-picking individual commits is not recommended or supported by the Linux kernel community at all. If however, updating to the latest release is impossible, the individual changes to resolve this issue can be found at these commits: https://git.kernel.org/stable/c/bdbc96c23197d773a7d1bf03e4f11de593b0ff28 https://git.kernel.org/stable/c/9bc18bb476e50e32e5d08f2734d63d63e0fa528c https://git.kernel.org/stable/c/8e9c0f500b42216ef930f5c0d1703989a451913d https://git.kernel.org/stable/c/50793801fc7f6d08def48754fb0f0706b0cfc394
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