{"api_version":"1","generated_at":"2026-08-22T09:26:13+00:00","cve":"CVE-2026-72108","urls":{"html":"https://cve.report/CVE-2026-72108","api":"https://cve.report/api/cve/CVE-2026-72108.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-72108","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-72108"},"summary":{"title":"dm thin metadata: fix metadata snapshot consistency on commit failure","description":"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's held_root directly in the block_manager's 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->held_root before btree deletion so\npartial failure leaks blocks rather than leaving a stale reference, and\nunlock the snapshot block before decrementing its refcount.","state":"PUBLISHED","assigner":"Linux","published_at":"2026-08-15 06:21:25","updated_at":"2026-08-17 06:18:09"},"problem_types":[],"metrics":[{"version":"3.1","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","type":"Secondary","score":"7.8","severity":"HIGH","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","data":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH","attackVector":"LOCAL","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH"}},{"version":"3.1","source":"CNA","type":"DECLARED","score":"7.8","severity":"HIGH","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","data":{"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"}}],"references":[{"url":"https://git.kernel.org/stable/c/7f76245960a332f39b08cc556e675d1765dc5bbb","name":"https://git.kernel.org/stable/c/7f76245960a332f39b08cc556e675d1765dc5bbb","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/abf2fae92cbe68945028987d498cc72f8f0e23a8","name":"https://git.kernel.org/stable/c/abf2fae92cbe68945028987d498cc72f8f0e23a8","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/3dc9ae1029320d77472c44965e572f176949cd63","name":"https://git.kernel.org/stable/c/3dc9ae1029320d77472c44965e572f176949cd63","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/9f1a0d27586ceab055e6b050e3731ce3c6b2c4f0","name":"https://git.kernel.org/stable/c/9f1a0d27586ceab055e6b050e3731ce3c6b2c4f0","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/4af993468193cf4cd32ba5748786e7801945f7d2","name":"https://git.kernel.org/stable/c/4af993468193cf4cd32ba5748786e7801945f7d2","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/b5f9a31c51cbb374a1713c3494f8660ab070f035","name":"https://git.kernel.org/stable/c/b5f9a31c51cbb374a1713c3494f8660ab070f035","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/5efb1a7734ed4035fa4fdc3716bdb84621f27cf6","name":"https://git.kernel.org/stable/c/5efb1a7734ed4035fa4fdc3716bdb84621f27cf6","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/5bcd4d3058ebaf46ad2e163829d87dd4870c7a45","name":"https://git.kernel.org/stable/c/5bcd4d3058ebaf46ad2e163829d87dd4870c7a45","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-72108","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-72108","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 991d9fa02da0dd1f843dc011376965e0c8c6c9b5 4af993468193cf4cd32ba5748786e7801945f7d2 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 991d9fa02da0dd1f843dc011376965e0c8c6c9b5 abf2fae92cbe68945028987d498cc72f8f0e23a8 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 991d9fa02da0dd1f843dc011376965e0c8c6c9b5 5efb1a7734ed4035fa4fdc3716bdb84621f27cf6 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 991d9fa02da0dd1f843dc011376965e0c8c6c9b5 3dc9ae1029320d77472c44965e572f176949cd63 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 991d9fa02da0dd1f843dc011376965e0c8c6c9b5 b5f9a31c51cbb374a1713c3494f8660ab070f035 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 991d9fa02da0dd1f843dc011376965e0c8c6c9b5 7f76245960a332f39b08cc556e675d1765dc5bbb git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 991d9fa02da0dd1f843dc011376965e0c8c6c9b5 9f1a0d27586ceab055e6b050e3731ce3c6b2c4f0 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 991d9fa02da0dd1f843dc011376965e0c8c6c9b5 5bcd4d3058ebaf46ad2e163829d87dd4870c7a45 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 3.2","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 3.2 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 5.10.261 5.10.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 5.15.212 5.15.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.1.178 6.1.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.6.145 6.6.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.12.97 6.12.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.18.40 6.18.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.1.5 7.1.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.2 * original_commit_for_fix","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":{"cve_year":"2026","cve_id":"72108","cve":"CVE-2026-72108","epss":"0.001640000","percentile":"0.060870000","score_date":"2026-08-17","updated_at":"2026-08-18 00:11:47"},"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"cna":{"affected":[{"defaultStatus":"unaffected","product":"Linux","programFiles":["drivers/md/dm-thin-metadata.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"lessThan":"4af993468193cf4cd32ba5748786e7801945f7d2","status":"affected","version":"991d9fa02da0dd1f843dc011376965e0c8c6c9b5","versionType":"git"},{"lessThan":"abf2fae92cbe68945028987d498cc72f8f0e23a8","status":"affected","version":"991d9fa02da0dd1f843dc011376965e0c8c6c9b5","versionType":"git"},{"lessThan":"5efb1a7734ed4035fa4fdc3716bdb84621f27cf6","status":"affected","version":"991d9fa02da0dd1f843dc011376965e0c8c6c9b5","versionType":"git"},{"lessThan":"3dc9ae1029320d77472c44965e572f176949cd63","status":"affected","version":"991d9fa02da0dd1f843dc011376965e0c8c6c9b5","versionType":"git"},{"lessThan":"b5f9a31c51cbb374a1713c3494f8660ab070f035","status":"affected","version":"991d9fa02da0dd1f843dc011376965e0c8c6c9b5","versionType":"git"},{"lessThan":"7f76245960a332f39b08cc556e675d1765dc5bbb","status":"affected","version":"991d9fa02da0dd1f843dc011376965e0c8c6c9b5","versionType":"git"},{"lessThan":"9f1a0d27586ceab055e6b050e3731ce3c6b2c4f0","status":"affected","version":"991d9fa02da0dd1f843dc011376965e0c8c6c9b5","versionType":"git"},{"lessThan":"5bcd4d3058ebaf46ad2e163829d87dd4870c7a45","status":"affected","version":"991d9fa02da0dd1f843dc011376965e0c8c6c9b5","versionType":"git"}]},{"defaultStatus":"affected","product":"Linux","programFiles":["drivers/md/dm-thin-metadata.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"status":"affected","version":"3.2"},{"lessThan":"3.2","status":"unaffected","version":"0","versionType":"semver"},{"lessThanOrEqual":"5.10.*","status":"unaffected","version":"5.10.261","versionType":"semver"},{"lessThanOrEqual":"5.15.*","status":"unaffected","version":"5.15.212","versionType":"semver"},{"lessThanOrEqual":"6.1.*","status":"unaffected","version":"6.1.178","versionType":"semver"},{"lessThanOrEqual":"6.6.*","status":"unaffected","version":"6.6.145","versionType":"semver"},{"lessThanOrEqual":"6.12.*","status":"unaffected","version":"6.12.97","versionType":"semver"},{"lessThanOrEqual":"6.18.*","status":"unaffected","version":"6.18.40","versionType":"semver"},{"lessThanOrEqual":"7.1.*","status":"unaffected","version":"7.1.5","versionType":"semver"},{"lessThanOrEqual":"*","status":"unaffected","version":"7.2","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"5.10.261","versionStartIncluding":"3.2","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"5.15.212","versionStartIncluding":"3.2","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.1.178","versionStartIncluding":"3.2","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.6.145","versionStartIncluding":"3.2","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.12.97","versionStartIncluding":"3.2","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.18.40","versionStartIncluding":"3.2","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.1.5","versionStartIncluding":"3.2","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.2","versionStartIncluding":"3.2","vulnerable":true}],"negate":false,"operator":"OR"}]}],"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's held_root directly in the block_manager's 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->held_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' data on shared LVM thin pools—storage-layer disclosure beyond the attacker's intended mapping.\nI:H - The same metadata inconsistency can double-allocate physical blocks or redirect writes to incorrect sectors, corrupting or overwriting other tenants' 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"},"nvd":{"publishedDate":"2026-08-15 06:21:25","lastModifiedDate":"2026-08-17 06:18:09","problem_types":[],"metrics":{"cvssMetricV31":[{"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","type":"Secondary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH","attackVector":"LOCAL","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH"},"exploitabilityScore":1.8,"impactScore":5.9}]},"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"72108","Ordinal":"1","Title":"dm thin metadata: fix metadata snapshot consistency on commit fa","CVE":"CVE-2026-72108","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"72108","Ordinal":"1","NoteData":"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's held_root directly in the block_manager's 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->held_root before btree deletion so\npartial failure leaks blocks rather than leaving a stale reference, and\nunlock the snapshot block before decrementing its refcount.","Type":"Description","Title":"dm thin metadata: fix metadata snapshot consistency on commit fa"}]}}}