CVE-2026-23342: Software Security Vulnerability Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-c898-7qpg-fw83",
  "modified" : "2026-04-23T21:31:18Z",
  "published" : "2026-03-25T12:30:23Z",
  "aliases" : [ "CVE-2026-23342" ],
  "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->count is reset in\n   bq_flush_to_queue(), a preempting task can call bq_enqueue() ->\n   bq_flush_to_queue() on the same bq when bq->count reaches\n   CPU_MAP_BULK_SIZE. Both tasks then call __list_del_clearprev()\n   on the same bq->flush_node, the second call dereferences the\n   prev pointer that was already set to NULL by the first.\n\n2. bq->count and bq->q[] 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 -> bq_flush_to_queue) and\ntask B (bq_enqueue -> 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(&q->producer_lock)\n    /* flush bq->q[] to ptr_ring */\n    bq->count = 0\n    spin_unlock(&q->producer_lock)\n                                   bq_enqueue(rcpu, xdpf)\n    <-- CFS preempts Task A -->      bq->q[bq->count++] = xdpf\n                                     /* ... more enqueues until full ... */\n                                     bq_flush_to_queue(bq)\n                                       spin_lock(&q->producer_lock)\n                                       /* flush to ptr_ring */\n                                       spin_unlock(&q->producer_lock)\n                                       __list_del_clearprev(flush_node)\n                                         /* sets flush_node.prev = NULL */\n    <-- Task A resumes -->\n    __list_del_clearprev(flush_node)\n      flush_node.prev->next = ...\n      /* prev is NULL -> 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->count = 0 and\n__list_del_clearprev() in bq_flush_to_queue(), then run reproducer\nprovided by syzkaller.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ ],
  "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"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-362" ],
    "severity" : "MODERATE",
    "github_reviewed" : false,
    "github_reviewed_at" : null,
    "nvd_published_at" : "2026-03-25T11:16:32Z"
  }
}