CVE-2025-68807 (GCVE-0-2025-68807)
Vulnerability from cvelistv5
Published
2026-01-13 15:29
Modified
2026-02-09 08:33
Severity ?
VLAI Severity ?
EPSS score ?
Summary
In the Linux kernel, the following vulnerability has been resolved:
block: fix race between wbt_enable_default and IO submission
When wbt_enable_default() is moved out of queue freezing in elevator_change(),
it can cause the wbt inflight counter to become negative (-1), leading to hung
tasks in the writeback path. Tasks get stuck in wbt_wait() because the counter
is in an inconsistent state.
The issue occurs because wbt_enable_default() could race with IO submission,
allowing the counter to be decremented before proper initialization. This manifests
as:
rq_wait[0]:
inflight: -1
has_waiters: True
rwb_enabled() checks the state, which can be updated exactly between wbt_wait()
(rq_qos_throttle()) and wbt_track()(rq_qos_track()), then the inflight counter
will become negative.
And results in hung task warnings like:
task:kworker/u24:39 state:D stack:0 pid:14767
Call Trace:
rq_qos_wait+0xb4/0x150
wbt_wait+0xa9/0x100
__rq_qos_throttle+0x24/0x40
blk_mq_submit_bio+0x672/0x7b0
...
Fix this by:
1. Splitting wbt_enable_default() into:
- __wbt_enable_default(): Returns true if wbt_init() should be called
- wbt_enable_default(): Wrapper for existing callers (no init)
- wbt_init_enable_default(): New function that checks and inits WBT
2. Using wbt_init_enable_default() in blk_register_queue() to ensure
proper initialization during queue registration
3. Move wbt_init() out of wbt_enable_default() which is only for enabling
disabled wbt from bfq and iocost, and wbt_init() isn't needed. Then the
original lock warning can be avoided.
4. Removing the ELEVATOR_FLAG_ENABLE_WBT_ON_EXIT flag and its handling
code since it's no longer needed
This ensures WBT is properly initialized before any IO can be submitted,
preventing the counter from going negative.
References
Impacted products
{
"containers": {
"cna": {
"affected": [
{
"defaultStatus": "unaffected",
"product": "Linux",
"programFiles": [
"block/bfq-iosched.c",
"block/blk-sysfs.c",
"block/blk-wbt.c",
"block/blk-wbt.h",
"block/elevator.c",
"block/elevator.h"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"lessThan": "f55201fb3becff6a903fd29f4d1147cc7e91eb0c",
"status": "affected",
"version": "78c271344b6f64ce24c845e54903e09928cf2061",
"versionType": "git"
},
{
"lessThan": "9869d3a6fed381f3b98404e26e1afc75d680cbf9",
"status": "affected",
"version": "78c271344b6f64ce24c845e54903e09928cf2061",
"versionType": "git"
}
]
},
{
"defaultStatus": "affected",
"product": "Linux",
"programFiles": [
"block/bfq-iosched.c",
"block/blk-sysfs.c",
"block/blk-wbt.c",
"block/blk-wbt.h",
"block/elevator.c",
"block/elevator.h"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"status": "affected",
"version": "6.16"
},
{
"lessThan": "6.16",
"status": "unaffected",
"version": "0",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.18.*",
"status": "unaffected",
"version": "6.18.3",
"versionType": "semver"
},
{
"lessThanOrEqual": "*",
"status": "unaffected",
"version": "6.19",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
{
"cpeMatch": [
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "6.18.3",
"versionStartIncluding": "6.16",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "6.19",
"versionStartIncluding": "6.16",
"vulnerable": true
}
],
"negate": false,
"operator": "OR"
}
]
}
],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nblock: fix race between wbt_enable_default and IO submission\n\nWhen wbt_enable_default() is moved out of queue freezing in elevator_change(),\nit can cause the wbt inflight counter to become negative (-1), leading to hung\ntasks in the writeback path. Tasks get stuck in wbt_wait() because the counter\nis in an inconsistent state.\n\nThe issue occurs because wbt_enable_default() could race with IO submission,\nallowing the counter to be decremented before proper initialization. This manifests\nas:\n\n rq_wait[0]:\n inflight: -1\n has_waiters: True\n\nrwb_enabled() checks the state, which can be updated exactly between wbt_wait()\n(rq_qos_throttle()) and wbt_track()(rq_qos_track()), then the inflight counter\nwill become negative.\n\nAnd results in hung task warnings like:\n task:kworker/u24:39 state:D stack:0 pid:14767\n Call Trace:\n rq_qos_wait+0xb4/0x150\n wbt_wait+0xa9/0x100\n __rq_qos_throttle+0x24/0x40\n blk_mq_submit_bio+0x672/0x7b0\n ...\n\nFix this by:\n\n1. Splitting wbt_enable_default() into:\n - __wbt_enable_default(): Returns true if wbt_init() should be called\n - wbt_enable_default(): Wrapper for existing callers (no init)\n - wbt_init_enable_default(): New function that checks and inits WBT\n\n2. Using wbt_init_enable_default() in blk_register_queue() to ensure\n proper initialization during queue registration\n\n3. Move wbt_init() out of wbt_enable_default() which is only for enabling\n disabled wbt from bfq and iocost, and wbt_init() isn\u0027t needed. Then the\n original lock warning can be avoided.\n\n4. Removing the ELEVATOR_FLAG_ENABLE_WBT_ON_EXIT flag and its handling\n code since it\u0027s no longer needed\n\nThis ensures WBT is properly initialized before any IO can be submitted,\npreventing the counter from going negative."
}
],
"providerMetadata": {
"dateUpdated": "2026-02-09T08:33:56.250Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"references": [
{
"url": "https://git.kernel.org/stable/c/f55201fb3becff6a903fd29f4d1147cc7e91eb0c"
},
{
"url": "https://git.kernel.org/stable/c/9869d3a6fed381f3b98404e26e1afc75d680cbf9"
}
],
"title": "block: fix race between wbt_enable_default and IO submission",
"x_generator": {
"engine": "bippy-1.2.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2025-68807",
"datePublished": "2026-01-13T15:29:14.483Z",
"dateReserved": "2025-12-24T10:30:51.045Z",
"dateUpdated": "2026-02-09T08:33:56.250Z",
"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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