CVE-2026-100073: ext4: fix transaction overflow during writeback
In the Linux kernel, the following vulnerability has been resolved:
ext4: fix transaction overflow during writeback
Commit 95ad8ee45cdb ("ext4: correct the reserved credits for extent conversion") was correct to note that we need to reserve enough credits for all extents possibly underlying a large folio. However it was too eager to reduce the number of reserved credits. Extent conversion may not only need to touch several leaf extent blocks, it may also need to split extents - for example a single large unwritten extent may need to be split into many small written ones in case of sparse folio dirtying. This can thus result not only in extent leaf modifications but also in a need to allocate new extent tree nodes. As a result the reserved transaction credits were not sufficient in some corner cases. Use ext4metatransblocks() for correct upper bound credit estimate.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Patch 95ad8ee45cdb
Event History
Frequently Asked Questions
Which filesystem workloads are most likely to encounter this issue?
The issue can occur during extent conversion for large folios, particularly when sparse dirtying requires a large unwritten extent to be split into multiple smaller written extents. These conversions can require both changes to multiple extent leaf blocks and allocation of new extent-tree nodes.
What is the immediate failure condition described for affected systems?
The transaction may reserve too few credits for the required extent conversion work. The insufficient reservation occurs in corner cases where extent splitting and new extent-tree node allocation are needed during writeback.