Copyright © 2012 Red Hat, Inc. All rights reserved. Important 2026-05-27T00:00:00 kernel: ext4: don't zero the entire extent if EXT4_EXT_DATA_PARTIAL_VALID1 7.0 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H CWE-909

In the Linux kernel, the following vulnerability has been resolved: ext4: don't zero the entire extent if EXT4_EXT_DATA_PARTIAL_VALID1 When allocating initialized blocks from a large unwritten extent, or when splitting an unwritten extent during end I/O and converting it to initialized, there is currently a potential issue of stale data if the extent needs to be split in the middle. 0 A B N [UUUUUUUUUUUU] U: unwritten extent [--DDDDDDDD--] D: valid data |<- ->| ----> this range needs to be initialized ext4_split_extent() first try to split this extent at B with EXT4_EXT_DATA_ENTIRE_VALID1 and EXT4_EXT_MAY_ZEROOUT flag set, but ext4_split_extent_at() failed to split this extent due to temporary lack of space. It zeroout B to N and mark the entire extent from 0 to N as written. 0 A B N [WWWWWWWWWWWW] W: written extent [SSDDDDDDDDZZ] Z: zeroed, S: stale data ext4_split_extent() then try to split this extent at A with EXT4_EXT_DATA_VALID2 flag set. This time, it split successfully and left a stale written extent from 0 to A. 0 A B N [WW|WWWWWWWWWW] [SS|DDDDDDDDZZ] Fix this by pass EXT4_EXT_DATA_PARTIAL_VALID1 to ext4_split_extent_at() when splitting at B, don't convert the entire extent to written and left it as unwritten after zeroing out B to N. The remaining work is just like the standard two-part split. ext4_split_extent() will pass the EXT4_EXT_DATA_VALID2 flag when it calls ext4_split_extent_at() for the second time, allowing it to properly handle the split. If the split is successful, it will keep extent from 0 to A as unwritten.

A flaw was found in the Linux kernel's ext4 filesystem. This vulnerability occurs during the splitting of unwritten data blocks, where a portion of the data may be incorrectly marked as written while still containing stale, uninitialized information. A local attacker could potentially exploit this to access sensitive data that should have been zeroed out, leading to information disclosure.

https://www.cve.org/CVERecord?id=CVE-2026-45858 https://nvd.nist.gov/vuln/detail/CVE-2026-45858 https://lore.kernel.org/linux-cve-announce/2026052710-CVE-2026-45858-54e5@gregkh/T