CVE-2026-89647
Estado: RecibidaAlta (7.5)—
In the Linux kernel, the following vulnerability has been resolved:
ceph: do not repeat ceph_trim_dentries() if no progress possible
ceph_cap_reclaim_work() re-queues itself for as long as ceph_trim_dentries() returns -EAGAIN, which happens whenever a lease walk exhausts its `nr_to_scan` budget. This creates a busy loop that consumes CPU without making any progress when there is nothing to reclaim: with no cap pressure (`count==0`) and every scanned lease still valid, each pass runs the full scan budget down to zero and returns `-EAGAIN`, only to be queued again immediately.
The dir-lease walk made this worse. When `expire_dir_lease` is `false` (i.e. we have no intention of reclaiming dir leases), __dir_lease_check() returned `TOUCH` for every valid lease. `TOUCH` moves the dentry to the tail of the list and resets `di->time` via __dentry_dir_lease_touch(), so a walk over N valid leases pointlessly rewrote the list, refreshed the timestamps (preventing them from ever aging out) and always drained `nr_to_scan`, guaranteeing the `-EAGAIN` requeue.
Leer descripción completaMostrar menos
Fix this in three steps:
Under real cap pressure (`count>0`) the reclaim path is unchanged and still retries via `-EAGAIN`.
Without this patch, I saw 500 ceph_trim_dentries() calls per second on our web servers. This is very visible in `/proc/lock_stat` (5 minute capture):
With this patch:
&mdsc->dentry_list_lock: 1203 1215 0.16 408.88 33082.88 27.23 4320501 7357389 0.04 500.64 1961578.00 0.27 ----------------------- &mdsc->dentry_list_lock 1029 [<000000003c9aea8a>] __ceph_dentry_dir_lease_touch+0x7c/0xa8 &mdsc->dentry_list_lock 1 ---truncated---
Detalles técnicos trazas, registros y código del informe original
- Return `KEEP` instead of `TOUCH` when `expire_dir_lease` is
`false`. If we are not going to reclaim the lease, leave it in
place instead of churning the list and resetting its timestamp; the
walk then terminates naturally (or via `STOP` at the first fresh
lease).
- Only return `-EAGAIN` from the first (dentry-lease) walk when something
was actually freed. A full batch that frees nothing means retrying
the same list immediately is futile; fall through to the dir-lease
walk instead.
- After both walks, bail out with success (0) when nothing was freed
and there is no cap pressure (`count==0`). There is no reason to
keep retrying when we are not over the cap limit and made no
progress.
class name con-bounces contentions waittime-min waittime-max waittime-total waittime-avg acq-bounces acquisitions holdtime-min holdtime-max holdtime-total holdtime-avg
&mdsc->dentry_list_lock: 126180 128218 0.04 8063.44 15986965.20 124.69 1573354 5296812 0.04 8291.28 74164526.48 14.00
-----------------------
&mdsc->dentry_list_lock 111736 [<000000007b11e319>] __ceph_dentry_dir_lease_touch+0x7c/0xa8
&mdsc->dentry_list_lock 2631 [<0000000050597999>] __dentry_leases_walk+0x64/0x2c8
&mdsc->dentry_list_lock 3878 [<00000000c0022f62>] __ceph_dentry_lease_touch+0x5c/0xa8
&mdsc->dentry_list_lock 9973 [<000000002f27cb6f>] __dentry_lease_unlist+0x50/0xa0
-----------------------
&mdsc->dentry_list_lock 123621 [<0000000050597999>] __dentry_leases_walk+0x64/0x2c8
&mdsc->dentry_list_lock 1822 [<000000007b11e319>] __ceph_dentry_dir_lease_touch+0x7c/0xa8
&mdsc->dentry_list_lock 2720 [<000000002f27cb6f>] __dentry_lease_unlist+0x50/0xa0
&mdsc->dentry_list_lock 55 [<00000000c0022f62>] __ceph_dentry_lease_touch+0x5c/0xa8
class name con-bounces contentions waittime-min waittime-max waittime-total waittime-avg acq-bounces acquisitions holdtime-min holdtime-max holdtime-total holdtime-avgCVSS
- Versión: 3.1
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Puntuación base: 7.5
Probabilidad de explotación (EPSS)
- Probabilidad de explotación en los próximos 30 días: 0.62%
- Percentil entre todas las CVEs puntuadas: 48
- Fecha de la puntuación: 6/10/2026
EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).
🎯 Técnicas ATT&CK
Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.
- Explotación
T1190Exploit Public-Facing Applicationinitial access60 % - Impacto principal
T1499Endpoint Denial of Serviceimpact55 %
Inferido por reglas deterministas a partir del vector CVSS y la CWE. Solo orientativo.
🛡️ Mitigaciones ATT&CK que cubren estas técnicas
Tecnologías afectadas (1)
⚠ Inferidas por IA a partir de la descripción — NVD aún no ha analizado esta CVE; no son CPE verificados.
Referencias
JSON original (NVD)
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{
"id": "CVE-2026-89647",
"cveTags": [],
"metrics": {
"cvssMetricV31": [
{
"type": "Secondary",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"cvssData": {
"scope": "UNCHANGED",
"version": "3.1",
"baseScore": 7.5,
"attackVector": "NETWORK",
"baseSeverity": "HIGH",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
"integrityImpact": "NONE",
"userInteraction": "NONE",
"attackComplexity": "LOW",
"availabilityImpact": "HIGH",
"privilegesRequired": "NONE",
"confidentialityImpact": "NONE"
},
"impactScore": 3.6,
"exploitabilityScore": 3.9
}
]
},
"affected": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"affectedData": [
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "37c4efc1ddf98ba8b234d116d863a9464445901e",
"lessThan": "5a541eb401acb89d791da41189d7a79220164b93",
"versionType": "git"
},
{
"status": "affected",
"version": "37c4efc1ddf98ba8b234d116d863a9464445901e",
"lessThan": "37d6edb2f03b29399a3a337fae78674de51e1695",
"versionType": "git"
},
{
"status": "affected",
"version": "37c4efc1ddf98ba8b234d116d863a9464445901e",
"lessThan": "3d122b2feb1dd76bb5041bdea5e1e1b007d8d415",
"versionType": "git"
},
{
"status": "affected",
"version": "37c4efc1ddf98ba8b234d116d863a9464445901e",
"lessThan": "e7d7aa7b730178278109c41fa1b17b06873065d5",
"versionType": "git"
}
],
"programFiles": [
"fs/ceph/dir.c"
],
"defaultStatus": "unaffected"
},
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "5.1"
},
{
"status": "unaffected",
"version": "0",
"lessThan": "5.1",
"versionType": "semver"
},
{
"status": "unaffected",
"version": "6.12.109",
"versionType": "semver",
"lessThanOrEqual": "6.12.*"
},
{
"status": "unaffected",
"version": "6.18.50",
"versionType": "semver",
"lessThanOrEqual": "6.18.*"
},
{
"status": "unaffected",
"version": "7.2.4",
"versionType": "semver",
"lessThanOrEqual": "7.2.*"
},
{
"status": "unaffected",
"version": "7.3-rc1",
"versionType": "original_commit_for_fix",
"lessThanOrEqual": "*"
}
],
"programFiles": [
"fs/ceph/dir.c"
],
"defaultStatus": "affected"
}
]
}
],
"published": "2026-09-11T20:19:50.607",
"references": [
{
"url": "https://git.kernel.org/stable/c/37d6edb2f03b29399a3a337fae78674de51e1695",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/3d122b2feb1dd76bb5041bdea5e1e1b007d8d415",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/5a541eb401acb89d791da41189d7a79220164b93",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/e7d7aa7b730178278109c41fa1b17b06873065d5",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}
],
"vulnStatus": "Received",
"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---"
}
],
"lastModified": "2026-09-13T07:17:29.837",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}