CVE-2026-45985
Analyzed Analyzed - Analysis Complete
Buffer Overflow in Linux Kernel ext4 Filesystem

Publication date: 2026-05-27

Last updated on: 2026-06-16

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: ext4: don't set EXT4_GET_BLOCKS_CONVERT when splitting before submitting I/O When allocating blocks during within-EOF DIO and writeback with dioread_nolock enabled, EXT4_GET_BLOCKS_PRE_IO was set to split an existing large unwritten extent. However, EXT4_GET_BLOCKS_CONVERT was set when calling ext4_split_convert_extents(), which may potentially result in stale data issues. Assume we have an unwritten extent, and then DIO writes the second half. [UUUUUUUUUUUUUUUU] on-disk extent U: unwritten extent [UUUUUUUUUUUUUUUU] extent status tree |<- ->| ----> dio write this range First, ext4_iomap_alloc() call ext4_map_blocks() with EXT4_GET_BLOCKS_PRE_IO, EXT4_GET_BLOCKS_UNWRIT_EXT and EXT4_GET_BLOCKS_CREATE flags set. ext4_map_blocks() find this extent and call ext4_split_convert_extents() with EXT4_GET_BLOCKS_CONVERT and the above flags set. Then, ext4_split_convert_extents() calls ext4_split_extent() with EXT4_EXT_MAY_ZEROOUT, EXT4_EXT_MARK_UNWRIT2 and EXT4_EXT_DATA_VALID2 flags set, and it calls ext4_split_extent_at() to split the second half with EXT4_EXT_DATA_VALID2, EXT4_EXT_MARK_UNWRIT1, EXT4_EXT_MAY_ZEROOUT and EXT4_EXT_MARK_UNWRIT2 flags set. However, ext4_split_extent_at() failed to insert extent since a temporary lack -ENOSPC. It zeroes out the first half but convert the entire on-disk extent to written since the EXT4_EXT_DATA_VALID2 flag set, but left the second half as unwritten in the extent status tree. [0000000000SSSSSS] data S: stale data, 0: zeroed [WWWWWWWWWWWWWWWW] on-disk extent W: written extent [WWWWWWWWWWUUUUUU] extent status tree Finally, if the DIO failed to write data to the disk, the stale data in the second half will be exposed once the cached extent entry is gone. Fix this issue by not passing EXT4_GET_BLOCKS_CONVERT when splitting an unwritten extent before submitting I/O, and make ext4_split_convert_extents() to zero out the entire extent range to zero for this case, and also mark the extent in the extent status tree for consistency.
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Meta Information
Published
2026-05-27
Last Modified
2026-06-16
Generated
2026-06-16
AI Q&A
2026-05-27
EPSS Evaluated
2026-06-15
NVD
CVE-2026-45985
EUVD
EUVD-2026-32270
Affected Vendors & Products
Showing 6 associated CPEs
Vendor Product Version / Range
linux linux_kernel From 6.19 (inc) to 6.19.4 (exc)
linux linux_kernel From 6.13 (inc) to 6.18.17 (exc)
linux linux_kernel From 6.7 (inc) to 6.12.77 (exc)
linux linux_kernel From 5.11 (inc) to 5.15.203 (exc)
linux linux_kernel From 3.15 (inc) to 5.10.253 (exc)
linux linux_kernel From 5.16 (inc) to 6.6.130 (exc)
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CWE ID Description
CWE-UNKNOWN
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Executive Summary

This vulnerability exists in the Linux kernel's ext4 filesystem. It occurs when splitting an unwritten extent during block allocation in direct I/O (DIO) and writeback operations with dioread_nolock enabled. The issue arises because the EXT4_GET_BLOCKS_CONVERT flag is incorrectly set when calling ext4_split_convert_extents(), which can cause stale data to be exposed.

Specifically, when a large unwritten extent is split before submitting I/O, the code mistakenly converts the entire on-disk extent to a written state while leaving part of the extent as unwritten in the extent status tree. If the DIO write fails, this mismatch can lead to stale (old, invalid) data being exposed to users.

The fix involves not setting the EXT4_GET_BLOCKS_CONVERT flag during the split and ensuring the entire extent is zeroed out and marked consistently to prevent stale data exposure.

Impact Analysis

This vulnerability can lead to exposure of stale data on disk. If a direct I/O write operation fails after splitting an unwritten extent, the system may incorrectly mark parts of the data as written while the actual data is stale or invalid.

As a result, users or applications reading the affected files might receive outdated or incorrect data, which can cause data integrity issues, application errors, or potential data leakage if sensitive information is involved.

Mitigation Strategies

The vulnerability is resolved by a fix in the Linux kernel that prevents setting EXT4_GET_BLOCKS_CONVERT when splitting an unwritten extent before submitting I/O.

To mitigate this vulnerability, you should update your Linux kernel to a version that includes this fix.

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