dm-thin: fix metadata refcount underflow

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Summary

CVECVE-2026-46107
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-28 10:16:26 UTC
Updated2026-05-28 13:44:01 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: dm-thin: fix metadata refcount underflow There's a bug in dm-thin in the function rebalance_children. If the internal btree node has one entry, the code tries to copy all btree entries from the node's child to the node itself and then decrement the child's reference count. If the child node is shared (it has reference count > 1), we won't free it, so there would be two pointers to each of the grandchildren nodes. But the reference counts of the grandchildren is not increased, thus the reference count doesn't match the number of pointers that point to the grandchildren. This results in "device mapper: space map common: unable to decrement block" errors. Fix this bug by incrementing reference counts on the grandchildren if the btree node is shared.

Risk And Classification

EPSS: 0.000180000 probability, percentile 0.051520000 (date 2026-05-28)

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 3241b1d3e0aaafbfcd320f4d71ade629728cc4f4 12161e03d33afce781f68fa11cc6060538862fad git Not specified
CNA Linux Linux affected 3241b1d3e0aaafbfcd320f4d71ade629728cc4f4 323d252a4a378834e4fe68298ca61cfc5dd3a460 git Not specified
CNA Linux Linux affected 3241b1d3e0aaafbfcd320f4d71ade629728cc4f4 85311a585a26640760cd0f3349ab9f2905691044 git Not specified
CNA Linux Linux affected 3241b1d3e0aaafbfcd320f4d71ade629728cc4f4 5ec0debbcfd43596e32c1239e993de06a704e04c git Not specified
CNA Linux Linux affected 3241b1d3e0aaafbfcd320f4d71ade629728cc4f4 09a65adc7d8bbfce06392cb6d375468e2728ead5 git Not specified
CNA Linux Linux affected 3.2 Not specified
CNA Linux Linux unaffected 3.2 semver Not specified
CNA Linux Linux unaffected 6.6.140 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.88 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.30 6.18.* semver Not specified
CNA Linux Linux unaffected 7.0.7 7.0.* semver Not specified
CNA Linux Linux unaffected 7.1-rc2 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/5ec0debbcfd43596e32c1239e993de06a704e04c 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/85311a585a26640760cd0f3349ab9f2905691044 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/12161e03d33afce781f68fa11cc6060538862fad 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/323d252a4a378834e4fe68298ca61cfc5dd3a460 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/09a65adc7d8bbfce06392cb6d375468e2728ead5 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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