CVE-2026-72108 (GCVE-0-2026-72108)
Vulnerability from cvelistv5
Published
2026-08-15 05:52
Modified
2026-08-17 05:40
Severity ?
VLAI Severity ?
EPSS score ?
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.
Bad reference count for metadata block 7. Expected 2, but space map contains 1.
Bad reference count for metadata block 13. Expected 1, but space map contains 0.
Reproducer 2: __release_metadata_snap()
1. Create a 2 MiB metadata device and make the region after the 16th
block inaccessible, to trigger metadata commit failure in the
subsequent release_metadata_snap operation. The 16th block will be
the shadow destination for the index block.
dmsetup create tmeta --table "0 128 linear /dev/sdc 0
128 3968 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. Reserve then release the metadata snapshot, to trigger metadata
commit failure and transaction abort. The held_root gets removed
from the on-disk superblock, causing inconsistent metadata.
dmsetup message tpool 0 "reserve_metadata_snap"
dmsetup message tpool 0 "release_metadata_snap"
thin_check v1.2.2 result:
Bad reference count for metadata block 6. Expected 1, but space map contains 2.
Bad reference count for metadata block 7. Expected 1, but space map contains 2.
1 metadata blocks have leaked.
Fix by deferring the held_root update to commit time.
Additionally, move the existing-snapshot check in __reserve_metadata_snap
before the shadow operation to avoid unnecessary work. In
__release_metadata_snap, clear pmd->held_root before btree deletion so
partial failure leaks blocks rather than leaving a stale reference, and
unlock the snapshot block before decrementing its refcount.
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| Linux | Linux |
Version: 991d9fa02da0dd1f843dc011376965e0c8c6c9b5 Version: 991d9fa02da0dd1f843dc011376965e0c8c6c9b5 Version: 991d9fa02da0dd1f843dc011376965e0c8c6c9b5 Version: 991d9fa02da0dd1f843dc011376965e0c8c6c9b5 Version: 991d9fa02da0dd1f843dc011376965e0c8c6c9b5 Version: 991d9fa02da0dd1f843dc011376965e0c8c6c9b5 Version: 991d9fa02da0dd1f843dc011376965e0c8c6c9b5 Version: 991d9fa02da0dd1f843dc011376965e0c8c6c9b5 |
||
{
"containers": {
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"versionType": "original_commit_for_fix"
}
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}
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"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\ndm thin metadata: fix metadata snapshot consistency on commit failure\n\n__reserve_metadata_snap() and __release_metadata_snap() modify the\nsuperblock\u0027s held_root directly in the block_manager\u0027s buffer. If the\nsubsequent metadata commit fails, the held_root gets flushed to disk\nthrough the abort_transaction path, resulting in inconsistent metadata.\n\nReproducer 1: __reserve_metadata_snap()\n\n1. Create a 2 MiB metadata device and make the region after the 14th\n block inaccessible, to trigger metadata commit failure in the\n subsequent reserve_metadata_snap operation. The 14th block will be\n the shadow destination for the index block.\n\ndmsetup create tmeta --table \"0 112 linear /dev/sdc 0\n112 3984 error\"\n\n2. Create a 16 MiB thin-pool\n\ndmsetup create tdata --table \"0 32768 zero\"\ndd if=/dev/zero of=/dev/mapper/tmeta bs=4k count=1\ndmsetup create tpool --table \"0 32768 thin-pool /dev/mapper/tmeta \\\n/dev/mapper/tdata 128 0 1 skip_block_zeroing\"\n\n3. Take a metadata snapshot to trigger metadata commit failure and\n transaction abort. However, the held_root is written to disk,\n breaking metadata consistency.\n\ndmsetup message tpool 0 \"reserve_metadata_snap\"\n\nthin_check v1.2.2 result:\n\nBad reference count for metadata block 6. Expected 2, but space map contains 1.\nBad reference count for metadata block 7. Expected 2, but space map contains 1.\nBad reference count for metadata block 13. Expected 1, but space map contains 0.\n\nReproducer 2: __release_metadata_snap()\n\n1. Create a 2 MiB metadata device and make the region after the 16th\n block inaccessible, to trigger metadata commit failure in the\n subsequent release_metadata_snap operation. The 16th block will be\n the shadow destination for the index block.\n\ndmsetup create tmeta --table \"0 128 linear /dev/sdc 0\n128 3968 error\"\n\n2. Create a 16 MiB thin-pool\n\ndmsetup create tdata --table \"0 32768 zero\"\ndd if=/dev/zero of=/dev/mapper/tmeta bs=4k count=1\ndmsetup create tpool --table \"0 32768 thin-pool /dev/mapper/tmeta \\\n/dev/mapper/tdata 128 0 1 skip_block_zeroing\"\n\n3. Reserve then release the metadata snapshot, to trigger metadata\n commit failure and transaction abort. The held_root gets removed\n from the on-disk superblock, causing inconsistent metadata.\n\ndmsetup message tpool 0 \"reserve_metadata_snap\"\ndmsetup message tpool 0 \"release_metadata_snap\"\n\nthin_check v1.2.2 result:\n\nBad reference count for metadata block 6. Expected 1, but space map contains 2.\nBad reference count for metadata block 7. Expected 1, but space map contains 2.\n1 metadata blocks have leaked.\n\nFix by deferring the held_root update to commit time.\n\nAdditionally, move the existing-snapshot check in __reserve_metadata_snap\nbefore the shadow operation to avoid unnecessary work. In\n__release_metadata_snap, clear pmd-\u003eheld_root before btree deletion so\npartial failure leaks blocks rather than leaving a stale reference, and\nunlock the snapshot block before decrementing its refcount."
}
],
"metrics": [
{
"cvssV3_1": {
"baseScore": 7.8,
"baseSeverity": "HIGH",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"scenarios": [
{
"lang": "en",
"value": "AV:L - The bug is reached only through local Device Mapper ioctls (dmsetup/LVM dm messages on /dev/mapper/control); reserve_metadata_snap and release_metadata_snap have no network, adjacent-wireless, or physical-device receive path.\nAC:L - An attacker with CAP_SYS_ADMIN who controls thin-pool creation can reliably force commit failure by mapping part of the metadata device to the dm error target (per the fix reproducer), deterministically hitting the flush-then-abort race.\nPR:L - DM ioctls require CAP_SYS_ADMIN, which is obtainable inside an unprivileged user namespace per kernel CNA guidance; thin-pool administration is commonly available to container/host admins with namespace capabilities, not only init-namespace root.\nUI:N - Exploitation requires only the attacker sending reserve_metadata_snap or release_metadata_snap via dmsetup/LVM; no separate victim user action such as opening a file or mounting a filesystem is needed.\nS:U - Corruption is confined to on-disk thin-pool metadata under the same host kernel and storage-admin security authority; it is not a KVM/Xen guest-to-host escape or cross-hypervisor boundary break.\nC:H - Persistently inconsistent btree/spacemap reference counts can mis-map logical blocks to wrong physical sectors, exposing stale or other thin volumes\u0027 data on shared LVM thin pools\u2014storage-layer disclosure beyond the attacker\u0027s intended mapping.\nI:H - The same metadata inconsistency can double-allocate physical blocks or redirect writes to incorrect sectors, corrupting or overwriting other tenants\u0027 data on multi-volume thin pools until thin_repair is performed.\nA:H - Commit failure leaves durable metadata corruption (thin_check refcount errors, leaked blocks), triggers needs_check, forces the pool into read-only/fail modes, and can render the pool unusable until offline repair."
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-08-17T05:40:21.561Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"references": [
{
"url": "https://git.kernel.org/stable/c/4af993468193cf4cd32ba5748786e7801945f7d2"
},
{
"url": "https://git.kernel.org/stable/c/abf2fae92cbe68945028987d498cc72f8f0e23a8"
},
{
"url": "https://git.kernel.org/stable/c/5efb1a7734ed4035fa4fdc3716bdb84621f27cf6"
},
{
"url": "https://git.kernel.org/stable/c/3dc9ae1029320d77472c44965e572f176949cd63"
},
{
"url": "https://git.kernel.org/stable/c/b5f9a31c51cbb374a1713c3494f8660ab070f035"
},
{
"url": "https://git.kernel.org/stable/c/7f76245960a332f39b08cc556e675d1765dc5bbb"
},
{
"url": "https://git.kernel.org/stable/c/9f1a0d27586ceab055e6b050e3731ce3c6b2c4f0"
},
{
"url": "https://git.kernel.org/stable/c/5bcd4d3058ebaf46ad2e163829d87dd4870c7a45"
}
],
"title": "dm thin metadata: fix metadata snapshot consistency on commit failure",
"x_generator": {
"engine": "bippy-1.2.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2026-72108",
"datePublished": "2026-08-15T05:52:50.321Z",
"dateReserved": "2026-08-09T03:40:39.906Z",
"dateUpdated": "2026-08-17T05:40:21.561Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.
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