CVE-2025-68807 (GCVE-0-2025-68807)

Vulnerability from cvelistv5 – Published: 2026-01-13 15:29 – Updated: 2026-02-09 08:33
VLAI?
Title
block: fix race between wbt_enable_default and IO submission
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.
Severity ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 78c271344b6f64ce24c845e54903e09928cf2061 , < f55201fb3becff6a903fd29f4d1147cc7e91eb0c (git)
Affected: 78c271344b6f64ce24c845e54903e09928cf2061 , < 9869d3a6fed381f3b98404e26e1afc75d680cbf9 (git)
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    Linux Linux Affected: 6.16
Unaffected: 0 , < 6.16 (semver)
Unaffected: 6.18.3 , ≤ 6.18.* (semver)
Unaffected: 6.19 , ≤ * (original_commit_for_fix)
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{
  "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": [
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              "status": "affected",
              "version": "78c271344b6f64ce24c845e54903e09928cf2061",
              "versionType": "git"
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              "status": "affected",
              "version": "78c271344b6f64ce24c845e54903e09928cf2061",
              "versionType": "git"
            }
          ]
        },
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          "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"
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              "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
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                  "versionEndExcluding": "6.19",
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                  "vulnerable": true
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              "negate": false,
              "operator": "OR"
            }
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      ],
      "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",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2025-68807",
      "date": "2026-04-18",
      "epss": "0.00027",
      "percentile": "0.07684"
    },
    "nvd": "{\"cve\":{\"id\":\"CVE-2025-68807\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2026-01-13T16:16:02.857\",\"lastModified\":\"2026-01-14T16:26:00.933\",\"vulnStatus\":\"Awaiting Analysis\",\"cveTags\":[],\"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.\"}],\"metrics\":{},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/9869d3a6fed381f3b98404e26e1afc75d680cbf9\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/f55201fb3becff6a903fd29f4d1147cc7e91eb0c\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}"
  }
}


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