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GHSA-C898-7QPG-FW83

Vulnerability from github – Published: 2026-03-25 12:30 – Updated: 2026-04-23 21:31

Details

In the Linux kernel, the following vulnerability has been resolved:

bpf: Fix race in cpumap on PREEMPT_RT

On PREEMPT_RT kernels, the per-CPU xdp_bulk_queue (bq) can be accessed concurrently by multiple preemptible tasks on the same CPU.

The original code assumes bq_enqueue() and __cpu_map_flush() run atomically with respect to each other on the same CPU, relying on local_bh_disable() to prevent preemption. However, on PREEMPT_RT, local_bh_disable() only calls migrate_disable() (when PREEMPT_RT_NEEDS_BH_LOCK is not set) and does not disable preemption, which allows CFS scheduling to preempt a task during bq_flush_to_queue(), enabling another task on the same CPU to enter bq_enqueue() and operate on the same per-CPU bq concurrently.

This leads to several races:

Double __list_del_clearprev(): after bq->count is reset in bq_flush_to_queue(), a preempting task can call bq_enqueue() -> bq_flush_to_queue() on the same bq when bq->count reaches CPU_MAP_BULK_SIZE. Both tasks then call __list_del_clearprev() on the same bq->flush_node, the second call dereferences the prev pointer that was already set to NULL by the first.
bq->count and bq->q[] races: concurrent bq_enqueue() can corrupt the packet queue while bq_flush_to_queue() is processing it.

The race between task A (__cpu_map_flush -> bq_flush_to_queue) and task B (bq_enqueue -> bq_flush_to_queue) on the same CPU:

Task A (xdp_do_flush) Task B (cpu_map_enqueue) ---------------------- ------------------------ bq_flush_to_queue(bq) spin_lock(&q->producer_lock) / flush bq->q[] to ptr_ring / bq->count = 0 spin_unlock(&q->producer_lock) bq_enqueue(rcpu, xdpf) <-- CFS preempts Task A --> bq->q[bq->count++] = xdpf / ... more enqueues until full ... / bq_flush_to_queue(bq) spin_lock(&q->producer_lock) / flush to ptr_ring / spin_unlock(&q->producer_lock) __list_del_clearprev(flush_node) / sets flush_node.prev = NULL / <-- Task A resumes --> __list_del_clearprev(flush_node) flush_node.prev->next = ... / prev is NULL -> kernel oops /

Fix this by adding a local_lock_t to xdp_bulk_queue and acquiring it in bq_enqueue() and __cpu_map_flush(). These paths already run under local_bh_disable(), so use local_lock_nested_bh() which on non-RT is a pure annotation with no overhead, and on PREEMPT_RT provides a per-CPU sleeping lock that serializes access to the bq.

To reproduce, insert an mdelay(100) between bq->count = 0 and __list_del_clearprev() in bq_flush_to_queue(), then run reproducer provided by syzkaller.

Severity

4.7 (Medium)


                  
                    CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H

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{
  "affected": [],
  "aliases": [
    "CVE-2026-23342"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-362"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-03-25T11:16:32Z",
    "severity": "MODERATE"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix race in cpumap on PREEMPT_RT\n\nOn PREEMPT_RT kernels, the per-CPU xdp_bulk_queue (bq) can be accessed\nconcurrently by multiple preemptible tasks on the same CPU.\n\nThe original code assumes bq_enqueue() and __cpu_map_flush() run\natomically with respect to each other on the same CPU, relying on\nlocal_bh_disable() to prevent preemption. However, on PREEMPT_RT,\nlocal_bh_disable() only calls migrate_disable() (when\nPREEMPT_RT_NEEDS_BH_LOCK is not set) and does not disable\npreemption, which allows CFS scheduling to preempt a task during\nbq_flush_to_queue(), enabling another task on the same CPU to enter\nbq_enqueue() and operate on the same per-CPU bq concurrently.\n\nThis leads to several races:\n\n1. Double __list_del_clearprev(): after bq-\u003ecount is reset in\n   bq_flush_to_queue(), a preempting task can call bq_enqueue() -\u003e\n   bq_flush_to_queue() on the same bq when bq-\u003ecount reaches\n   CPU_MAP_BULK_SIZE. Both tasks then call __list_del_clearprev()\n   on the same bq-\u003eflush_node, the second call dereferences the\n   prev pointer that was already set to NULL by the first.\n\n2. bq-\u003ecount and bq-\u003eq[] races: concurrent bq_enqueue() can corrupt\n   the packet queue while bq_flush_to_queue() is processing it.\n\nThe race between task A (__cpu_map_flush -\u003e bq_flush_to_queue) and\ntask B (bq_enqueue -\u003e bq_flush_to_queue) on the same CPU:\n\n  Task A (xdp_do_flush)          Task B (cpu_map_enqueue)\n  ----------------------         ------------------------\n  bq_flush_to_queue(bq)\n    spin_lock(\u0026q-\u003eproducer_lock)\n    /* flush bq-\u003eq[] to ptr_ring */\n    bq-\u003ecount = 0\n    spin_unlock(\u0026q-\u003eproducer_lock)\n                                   bq_enqueue(rcpu, xdpf)\n    \u003c-- CFS preempts Task A --\u003e      bq-\u003eq[bq-\u003ecount++] = xdpf\n                                     /* ... more enqueues until full ... */\n                                     bq_flush_to_queue(bq)\n                                       spin_lock(\u0026q-\u003eproducer_lock)\n                                       /* flush to ptr_ring */\n                                       spin_unlock(\u0026q-\u003eproducer_lock)\n                                       __list_del_clearprev(flush_node)\n                                         /* sets flush_node.prev = NULL */\n    \u003c-- Task A resumes --\u003e\n    __list_del_clearprev(flush_node)\n      flush_node.prev-\u003enext = ...\n      /* prev is NULL -\u003e kernel oops */\n\nFix this by adding a local_lock_t to xdp_bulk_queue and acquiring it\nin bq_enqueue() and __cpu_map_flush(). These paths already run under\nlocal_bh_disable(), so use local_lock_nested_bh() which on non-RT is\na pure annotation with no overhead, and on PREEMPT_RT provides a\nper-CPU sleeping lock that serializes access to the bq.\n\nTo reproduce, insert an mdelay(100) between bq-\u003ecount = 0 and\n__list_del_clearprev() in bq_flush_to_queue(), then run reproducer\nprovided by syzkaller.",
  "id": "GHSA-c898-7qpg-fw83",
  "modified": "2026-04-23T21:31:18Z",
  "published": "2026-03-25T12:30:23Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-23342"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/7466ae2aeed483de80c5d8dea0913cf74038b652"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/869c63d5975d55e97f6b168e885452b3da20ea47"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/e67299e1044349ad0088d52c6bc5764cc1816c06"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}

CVE-2026-23342 (GCVE-0-2026-23342)

Vulnerability from cvelistv5 – Published: 2026-03-25 10:27 – Updated: 2026-05-11 22:04

Title

bpf: Fix race in cpumap on PREEMPT_RT

Summary

In the Linux kernel, the following vulnerability has been resolved: bpf: Fix race in cpumap on PREEMPT_RT On PREEMPT_RT kernels, the per-CPU xdp_bulk_queue (bq) can be accessed concurrently by multiple preemptible tasks on the same CPU. The original code assumes bq_enqueue() and __cpu_map_flush() run atomically with respect to each other on the same CPU, relying on local_bh_disable() to prevent preemption. However, on PREEMPT_RT, local_bh_disable() only calls migrate_disable() (when PREEMPT_RT_NEEDS_BH_LOCK is not set) and does not disable preemption, which allows CFS scheduling to preempt a task during bq_flush_to_queue(), enabling another task on the same CPU to enter bq_enqueue() and operate on the same per-CPU bq concurrently. This leads to several races: 1. Double __list_del_clearprev(): after bq->count is reset in bq_flush_to_queue(), a preempting task can call bq_enqueue() -> bq_flush_to_queue() on the same bq when bq->count reaches CPU_MAP_BULK_SIZE. Both tasks then call __list_del_clearprev() on the same bq->flush_node, the second call dereferences the prev pointer that was already set to NULL by the first. 2. bq->count and bq->q[] races: concurrent bq_enqueue() can corrupt the packet queue while bq_flush_to_queue() is processing it. The race between task A (__cpu_map_flush -> bq_flush_to_queue) and task B (bq_enqueue -> bq_flush_to_queue) on the same CPU: Task A (xdp_do_flush) Task B (cpu_map_enqueue) ---------------------- ------------------------ bq_flush_to_queue(bq) spin_lock(&q->producer_lock) /* flush bq->q[] to ptr_ring */ bq->count = 0 spin_unlock(&q->producer_lock) bq_enqueue(rcpu, xdpf) <-- CFS preempts Task A --> bq->q[bq->count++] = xdpf /* ... more enqueues until full ... */ bq_flush_to_queue(bq) spin_lock(&q->producer_lock) /* flush to ptr_ring */ spin_unlock(&q->producer_lock) __list_del_clearprev(flush_node) /* sets flush_node.prev = NULL */ <-- Task A resumes --> __list_del_clearprev(flush_node) flush_node.prev->next = ... /* prev is NULL -> kernel oops */ Fix this by adding a local_lock_t to xdp_bulk_queue and acquiring it in bq_enqueue() and __cpu_map_flush(). These paths already run under local_bh_disable(), so use local_lock_nested_bh() which on non-RT is a pure annotation with no overhead, and on PREEMPT_RT provides a per-CPU sleeping lock that serializes access to the bq. To reproduce, insert an mdelay(100) between bq->count = 0 and __list_del_clearprev() in bq_flush_to_queue(), then run reproducer provided by syzkaller.

Severity

No CVSS data available.

Assigner

Linux mitre root

References

3 references

URL	Tags
https://git.kernel.org/stable/c/7466ae2aeed483de8…
https://git.kernel.org/stable/c/e67299e1044349ad0…
https://git.kernel.org/stable/c/869c63d5975d55e97…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: 3253cb49cbad4772389d6ef55be75db1f97da910 , < 7466ae2aeed483de80c5d8dea0913cf74038b652 (git) Affected: 3253cb49cbad4772389d6ef55be75db1f97da910 , < e67299e1044349ad0088d52c6bc5764cc1816c06 (git) Affected: 3253cb49cbad4772389d6ef55be75db1f97da910 , < 869c63d5975d55e97f6b168e885452b3da20ea47 (git)
Linux	Linux	Affected: 6.18 Unaffected: 0 , < 6.18 (semver) Unaffected: 6.18.17 , ≤ 6.18.* (semver) Unaffected: 6.19.7 , ≤ 6.19.* (semver) Unaffected: 7.0 , ≤ * (original_commit_for_fix)

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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "kernel/bpf/cpumap.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "7466ae2aeed483de80c5d8dea0913cf74038b652",
              "status": "affected",
              "version": "3253cb49cbad4772389d6ef55be75db1f97da910",
              "versionType": "git"
            },
            {
              "lessThan": "e67299e1044349ad0088d52c6bc5764cc1816c06",
              "status": "affected",
              "version": "3253cb49cbad4772389d6ef55be75db1f97da910",
              "versionType": "git"
            },
            {
              "lessThan": "869c63d5975d55e97f6b168e885452b3da20ea47",
              "status": "affected",
              "version": "3253cb49cbad4772389d6ef55be75db1f97da910",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "kernel/bpf/cpumap.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.18"
            },
            {
              "lessThan": "6.18",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.17",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.19.*",
              "status": "unaffected",
              "version": "6.19.7",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.0",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.17",
                  "versionStartIncluding": "6.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.19.7",
                  "versionStartIncluding": "6.18",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.0",
                  "versionStartIncluding": "6.18",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix race in cpumap on PREEMPT_RT\n\nOn PREEMPT_RT kernels, the per-CPU xdp_bulk_queue (bq) can be accessed\nconcurrently by multiple preemptible tasks on the same CPU.\n\nThe original code assumes bq_enqueue() and __cpu_map_flush() run\natomically with respect to each other on the same CPU, relying on\nlocal_bh_disable() to prevent preemption. However, on PREEMPT_RT,\nlocal_bh_disable() only calls migrate_disable() (when\nPREEMPT_RT_NEEDS_BH_LOCK is not set) and does not disable\npreemption, which allows CFS scheduling to preempt a task during\nbq_flush_to_queue(), enabling another task on the same CPU to enter\nbq_enqueue() and operate on the same per-CPU bq concurrently.\n\nThis leads to several races:\n\n1. Double __list_del_clearprev(): after bq-\u003ecount is reset in\n   bq_flush_to_queue(), a preempting task can call bq_enqueue() -\u003e\n   bq_flush_to_queue() on the same bq when bq-\u003ecount reaches\n   CPU_MAP_BULK_SIZE. Both tasks then call __list_del_clearprev()\n   on the same bq-\u003eflush_node, the second call dereferences the\n   prev pointer that was already set to NULL by the first.\n\n2. bq-\u003ecount and bq-\u003eq[] races: concurrent bq_enqueue() can corrupt\n   the packet queue while bq_flush_to_queue() is processing it.\n\nThe race between task A (__cpu_map_flush -\u003e bq_flush_to_queue) and\ntask B (bq_enqueue -\u003e bq_flush_to_queue) on the same CPU:\n\n  Task A (xdp_do_flush)          Task B (cpu_map_enqueue)\n  ----------------------         ------------------------\n  bq_flush_to_queue(bq)\n    spin_lock(\u0026q-\u003eproducer_lock)\n    /* flush bq-\u003eq[] to ptr_ring */\n    bq-\u003ecount = 0\n    spin_unlock(\u0026q-\u003eproducer_lock)\n                                   bq_enqueue(rcpu, xdpf)\n    \u003c-- CFS preempts Task A --\u003e      bq-\u003eq[bq-\u003ecount++] = xdpf\n                                     /* ... more enqueues until full ... */\n                                     bq_flush_to_queue(bq)\n                                       spin_lock(\u0026q-\u003eproducer_lock)\n                                       /* flush to ptr_ring */\n                                       spin_unlock(\u0026q-\u003eproducer_lock)\n                                       __list_del_clearprev(flush_node)\n                                         /* sets flush_node.prev = NULL */\n    \u003c-- Task A resumes --\u003e\n    __list_del_clearprev(flush_node)\n      flush_node.prev-\u003enext = ...\n      /* prev is NULL -\u003e kernel oops */\n\nFix this by adding a local_lock_t to xdp_bulk_queue and acquiring it\nin bq_enqueue() and __cpu_map_flush(). These paths already run under\nlocal_bh_disable(), so use local_lock_nested_bh() which on non-RT is\na pure annotation with no overhead, and on PREEMPT_RT provides a\nper-CPU sleeping lock that serializes access to the bq.\n\nTo reproduce, insert an mdelay(100) between bq-\u003ecount = 0 and\n__list_del_clearprev() in bq_flush_to_queue(), then run reproducer\nprovided by syzkaller."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-05-11T22:04:59.186Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
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          "url": "https://git.kernel.org/stable/c/7466ae2aeed483de80c5d8dea0913cf74038b652"
        },
        {
          "url": "https://git.kernel.org/stable/c/e67299e1044349ad0088d52c6bc5764cc1816c06"
        },
        {
          "url": "https://git.kernel.org/stable/c/869c63d5975d55e97f6b168e885452b3da20ea47"
        }
      ],
      "title": "bpf: Fix race in cpumap on PREEMPT_RT",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-23342",
    "datePublished": "2026-03-25T10:27:30.285Z",
    "dateReserved": "2026-01-13T15:37:45.999Z",
    "dateUpdated": "2026-05-11T22:04:59.186Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

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Nomenclature

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Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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GHSA-C898-7QPG-FW83

CVE-2026-23342 (GCVE-0-2026-23342)

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