bpf: Fix race in devmap on PREEMPT_RT_CVE-2026-23294

{
    "lastseen": "",
    "description": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix race in devmap on PREEMPT_RT\n\nOn PREEMPT_RT kernels, the per-CPU xdp_dev_bulk_queue (bq) can be\naccessed concurrently by multiple preemptible tasks on the same CPU.\n\nThe original code assumes bq_enqueue() and __dev_flush() run atomically\nwith 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_xmit_all(), 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-free / use-after-free on bq->q[]: bq_xmit_all() snapshots\n   cnt = bq->count, then iterates bq->q[0..cnt-1] to transmit frames.\n   If preempted after the snapshot, a second task can call bq_enqueue()\n   -> bq_xmit_all() on the same bq, transmitting (and freeing) the\n   same frames. When the first task resumes, it operates on stale\n   pointers in bq->q[], causing use-after-free.\n\n2. bq->count and bq->q[] corruption: concurrent bq_enqueue() modifying\n   bq->count and bq->q[] while bq_xmit_all() is reading them.\n\n3. dev_rx/xdp_prog teardown race: __dev_flush() clears bq->dev_rx and\n   bq->xdp_prog after bq_xmit_all(). If preempted between\n   bq_xmit_all() return and bq->dev_rx = NULL, a preempting\n   bq_enqueue() sees dev_rx still set (non-NULL), skips adding bq to\n   the flush_list, and enqueues a frame. When __dev_flush() resumes,\n   it clears dev_rx and removes bq from the flush_list, orphaning the\n   newly enqueued frame.\n\n4. __list_del_clearprev() on flush_node: similar to the cpumap race,\n   both tasks can call __list_del_clearprev() on the same flush_node,\n   the second dereferences the prev pointer already set to NULL.\n\nThe race between task A (__dev_flush -> bq_xmit_all) and task B\n(bq_enqueue -> bq_xmit_all) on the same CPU:\n\n  Task A (xdp_do_flush)          Task B (ndo_xdp_xmit redirect)\n  ----------------------         --------------------------------\n  __dev_flush(flush_list)\n    bq_xmit_all(bq)\n      cnt = bq->count  /* e.g. 16 */\n      /* start iterating bq->q[] */\n    <-- CFS preempts Task A -->\n                                   bq_enqueue(dev, xdpf)\n                                     bq->count == DEV_MAP_BULK_SIZE\n                                     bq_xmit_all(bq, 0)\n                                       cnt = bq->count  /* same 16! */\n                                       ndo_xdp_xmit(bq->q[])\n                                       /* frames freed by driver */\n                                       bq->count = 0\n    <-- Task A resumes -->\n      ndo_xdp_xmit(bq->q[])\n      /* use-after-free: frames already freed! */\n\nFix this by adding a local_lock_t to xdp_dev_bulk_queue and acquiring\nit in bq_enqueue() and __dev_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.",
    "published": "2026-03-25T10:26:51.946Z",
    "modified": "2026-04-02T14:44:14.096Z",
    "type": "cve",
    "title": "bpf: Fix race in devmap on PREEMPT_RT",
    "source": "Linux",
    "references": "https://git.kernel.org/stable/c/6c10b019785dc282c5f45d21e4a3f468b8fd6476\nhttps://git.kernel.org/stable/c/ab1a56c9d99189aa5c6e03940d06e40ba6a28240\nhttps://git.kernel.org/stable/c/1872e75375c40add4a35990de3be77b5741c252c",
    "id": "CVE-2026-23294",
    "bulletinFamily": "",
    "cwe": null,
    "cvelist": null,
    "sourceData": "Linux Linux 3253cb49cbad4772389d6ef55be75db1f97da910\nLinux Linux 3253cb49cbad4772389d6ef55be75db1f97da910\nLinux Linux 3253cb49cbad4772389d6ef55be75db1f97da910\nLinux Linux 6.18",
    "sourceHref": "",
    "cvss": {
        "score": 7,
        "severity": "HIGH",
        "vector": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H",
        "version": "3.1"
    },
    "cvss2": [],
    "cvss3": {
        "version": "",
        "vectorString": "",
        "baseScore": 0,
        "baseSeverity": "",
        "attackVector": "",
        "attackComplexity": "",
        "privilegesRequired": "",
        "userInteraction": "",
        "scope": "",
        "confidentialityImpact": "",
        "integrityImpact": "",
        "availabilityImpact": "",
        "cvssV3": {
            "version": "",
            "vectorString": "",
            "baseScore": 0,
            "baseSeverity": "",
            "attackVector": "",
            "attackComplexity": "",
            "privilegesRequired": "",
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            "scope": "",
            "confidentialityImpact": "",
            "integrityImpact": "",
            "availabilityImpact": ""
        }
    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "Linux",
    "version": "3253cb49cbad4772389d6ef55be75db1f97da910",
    "vendor": "Linux",
    "ai_description": "",
    "ai_severity": "",
    "ai_vendor": "",
    "ai_product": "",
    "ai_version": "",
    "ai_score": 0
}