{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-89647", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-09-11T19:38:34.741Z", "datePublished": "2026-09-11T19:45:38.593Z", "dateUpdated": "2026-10-21T12:48:11.164Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-10-21T12:48:11.164Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nceph: do not repeat ceph_trim_dentries() if no progress possible\n\nceph_cap_reclaim_work() re-queues itself for as long as\nceph_trim_dentries() returns -EAGAIN, which happens whenever a lease\nwalk exhausts its `nr_to_scan` budget. This creates a busy loop that\nconsumes CPU without making any progress when there is nothing to\nreclaim: with no cap pressure (`count==0`) and every scanned lease\nstill valid, each pass runs the full scan budget down to zero and\nreturns `-EAGAIN`, only to be queued again immediately.\n\nThe dir-lease walk made this worse. When `expire_dir_lease` is\n`false` (i.e. we have no intention of reclaiming dir leases),\n__dir_lease_check() returned `TOUCH` for every valid lease. `TOUCH`\nmoves the dentry to the tail of the list and resets `di->time` via\n__dentry_dir_lease_touch(), so a walk over N valid leases pointlessly\nrewrote the list, refreshed the timestamps (preventing them from ever\naging out) and always drained `nr_to_scan`, guaranteeing the `-EAGAIN`\nrequeue.\n\nFix this in three steps:\n\n - Return `KEEP` instead of `TOUCH` when `expire_dir_lease` is\n `false`. If we are not going to reclaim the lease, leave it in\n place instead of churning the list and resetting its timestamp; the\n walk then terminates naturally (or via `STOP` at the first fresh\n lease).\n\n - Only return `-EAGAIN` from the first (dentry-lease) walk when something\n was actually freed. A full batch that frees nothing means retrying\n the same list immediately is futile; fall through to the dir-lease\n walk instead.\n\n - After both walks, bail out with success (0) when nothing was freed\n and there is no cap pressure (`count==0`). There is no reason to\n keep retrying when we are not over the cap limit and made no\n progress.\n\nUnder real cap pressure (`count>0`) the reclaim path is unchanged and\nstill retries via `-EAGAIN`.\n\nWithout this patch, I saw 500 ceph_trim_dentries() calls per second on\nour web servers. This is very visible in `/proc/lock_stat` (5 minute\ncapture):\n\n class name con-bounces contentions waittime-min waittime-max waittime-total waittime-avg acq-bounces acquisitions holdtime-min holdtime-max holdtime-total holdtime-avg\n\n &mdsc->dentry_list_lock: 126180 128218 0.04 8063.44 15986965.20 124.69 1573354 5296812 0.04 8291.28 74164526.48 14.00\n -----------------------\n &mdsc->dentry_list_lock 111736 [<000000007b11e319>] __ceph_dentry_dir_lease_touch+0x7c/0xa8\n &mdsc->dentry_list_lock 2631 [<0000000050597999>] __dentry_leases_walk+0x64/0x2c8\n &mdsc->dentry_list_lock 3878 [<00000000c0022f62>] __ceph_dentry_lease_touch+0x5c/0xa8\n &mdsc->dentry_list_lock 9973 [<000000002f27cb6f>] __dentry_lease_unlist+0x50/0xa0\n -----------------------\n &mdsc->dentry_list_lock 123621 [<0000000050597999>] __dentry_leases_walk+0x64/0x2c8\n &mdsc->dentry_list_lock 1822 [<000000007b11e319>] __ceph_dentry_dir_lease_touch+0x7c/0xa8\n &mdsc->dentry_list_lock 2720 [<000000002f27cb6f>] __dentry_lease_unlist+0x50/0xa0\n &mdsc->dentry_list_lock 55 [<00000000c0022f62>] __ceph_dentry_lease_touch+0x5c/0xa8\n\nWith this patch:\n\n class name con-bounces contentions waittime-min waittime-max waittime-total waittime-avg acq-bounces acquisitions holdtime-min holdtime-max holdtime-total holdtime-avg\n\n &mdsc->dentry_list_lock: 1203 1215 0.16 408.88 33082.88 27.23 4320501 7357389 0.04 500.64 1961578.00 0.27\n -----------------------\n &mdsc->dentry_list_lock 1029 [<000000003c9aea8a>] __ceph_dentry_dir_lease_touch+0x7c/0xa8\n &mdsc->dentry_list_lock 1\n---truncated---" } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "baseScore": 7.5, "baseSeverity": "HIGH" }, "scenarios": [ { "lang": "en", "value": "AV:N - fs/ceph registers ceph_export_ops, so remote nfsd/ksmbd readdir and lookup on an exported CephFS mount populate dentry and dir-lease lists and drive ceph_trim_dentries() via the cap-reclaim workqueue; a compromised MDS on the existing client TCP session can also keep those leases valid.\nAC:L - Default caps_max leaves count==0, so expire_dir_lease is false and valid dir leases are TOUCHed until nr_to_scan hits zero; ceph_cap_reclaim_work() then immediately requeues on -EAGAIN. An attacker who walks or creates many dentries, or a peer that grants many still-valid leases, triggers this deterministically with no race.\nPR:N - In the network-export scenario the attacker needs no local account or capability on the victim host; guest or anonymous NFS/SMB exports of CephFS, and a remote MDS peer on an already-connected kernel client, are reasonable high-severity deployments matching other Ceph client CVEs.\nUI:N - After CephFS is mounted and optionally exported, delayed_work periodically queues reclaim and the attacker’s own readdir/lookup or MDS lease traffic is enough; no separate victim mount, open, or confirmation is required at exploit time.\nS:U - The busy loop, CPU burn, and dentry_list_lock contention stay inside the host kernel CephFS client and do not cross a VM, IOMMU, or sandbox boundary to another security authority.\nC:N - The defect only rescans and TOUCHes still-valid dentry leases; it does not perform an out-of-bounds read, use-after-free, or any other kernel-memory disclosure.\nI:N - The walk only reshuffles lease-list order and refreshes dentry timestamps; there is no memory corruption, arbitrary write, or control-flow hijack primitive.\nA:H - ceph_cap_reclaim_work() immediately requeues itself on -EAGAIN, forming an unbounded busy loop on the max_active=1 ceph-cap workqueue (observed ~500 iterations/s) that starves cap-release work, burns CPU, and contends dentry_list_lock enough to stall Ceph directory operations." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/ceph/dir.c" ], "versions": [ { "version": "37c4efc1ddf98ba8b234d116d863a9464445901e", "lessThan": "dd2e9824e5e7dba406005ff779a107f773175a76", "status": "affected", "versionType": "git" }, { "version": "37c4efc1ddf98ba8b234d116d863a9464445901e", "lessThan": "5a541eb401acb89d791da41189d7a79220164b93", "status": "affected", "versionType": "git" }, { "version": "37c4efc1ddf98ba8b234d116d863a9464445901e", "lessThan": "37d6edb2f03b29399a3a337fae78674de51e1695", "status": "affected", "versionType": "git" }, { "version": "37c4efc1ddf98ba8b234d116d863a9464445901e", "lessThan": "3d122b2feb1dd76bb5041bdea5e1e1b007d8d415", "status": "affected", "versionType": "git" }, { "version": "37c4efc1ddf98ba8b234d116d863a9464445901e", "lessThan": "e7d7aa7b730178278109c41fa1b17b06873065d5", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/ceph/dir.c" ], "versions": [ { "version": "5.1", "status": "affected" }, { "version": "0", "lessThan": "5.1", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.160", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.109", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.50", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.2.4", "lessThanOrEqual": "7.2.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.3", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.1", "versionEndExcluding": "6.6.160" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.1", "versionEndExcluding": "6.12.109" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.1", "versionEndExcluding": "6.18.50" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.1", "versionEndExcluding": "7.2.4" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.1", "versionEndExcluding": "7.3" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/dd2e9824e5e7dba406005ff779a107f773175a76" }, { "url": "https://git.kernel.org/stable/c/5a541eb401acb89d791da41189d7a79220164b93" }, { "url": "https://git.kernel.org/stable/c/37d6edb2f03b29399a3a337fae78674de51e1695" }, { "url": "https://git.kernel.org/stable/c/3d122b2feb1dd76bb5041bdea5e1e1b007d8d415" }, { "url": "https://git.kernel.org/stable/c/e7d7aa7b730178278109c41fa1b17b06873065d5" } ], "title": "ceph: do not repeat ceph_trim_dentries() if no progress possible", "x_generator": { "engine": "bippy-1.2.0" } }, "adp": [ { "metrics": [ { "other": { "type": "ssvc", "content": { "id": "CVE-2026-89647", "role": "CISA Coordinator", "options": [ { "Exploitation": "none" }, { "Automatable": "yes" }, { "Technical Impact": "partial" } ], "version": "2.0.3", "timestamp": "2026-10-16T19:25:05.998836Z" } } } ], "title": "CISA ADP Vulnrichment", "providerMetadata": { "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-10-16T19:26:46.221Z" } } ] } }