Medium [CVE-2026-72108] dm thin metadata: fix metadata snapshot consistency on commit failure
This medium-severity Red Hat Linux advisory covers CVE-2026-72108 affecting Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7.
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Summary
In the Linux kernel, the following vulnerability has been resolved: dm thin metadata: fix metadata snapshot consistency on commit failure __reserve_metadata_snap() and __release_metadata_snap() modify the superblock's held_root directly in the block_manager's buffer.
If the subsequent metadata commit fails, the held_root gets flushed to disk through the abort_transaction path, resulting in inconsistent metadata. Reproducer 1: __reserve_metadata_snap() 1.
Create a 2 MiB metadata device and make the region after the 14th block inaccessible, to trigger metadata commit failure in the subsequent reserve_metadata_snap operation. The 14th block will be the shadow destination for the index block. dmsetup create tmeta --table "0 112 linear /dev/sdc 0 112 3984 error" 2.
Create a 16 MiB thin-pool dmsetup create tdata --table "0 32768 zero" dd if=/dev/zero of=/dev/mapper/tmeta bs=4k count=1 dmsetup create tpool --table "0 32768 thin-pool /dev/mapper/tmeta \ /dev/mapper/tdata 128 0 1 skip_block_zeroing" 3. Take a metadata snapshot to trigger metadata commit failure and transaction abort.
However, the held_root is written to disk, breaking metadata consistency. dmsetup message tpool 0 "reserve_metadata_snap" thin_check v1.2.2 result: Bad reference count for metadata block 6. Expected 2, but space map contains 1.
Reproducer 2: __release_metadata_snap() 1. 1 metadata blocks have leaked.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · medium-confidence parse· fetched 25 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · medium-confidence parse· fetched 25 days ago·verify at source
Mitigation
The source record does not include mitigation steps. That is not a statement that no fix exists — read the vendor advisory below for the authoritative guidance.
Official advisory · medium-confidence parse· fetched 25 days ago·verify at source
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