{"cve":"CVE-2026-23342","nvd":{"published":"2026-03-25T11:16:32.147","modified":"2026-06-17T10:21:22.597","status":"Analyzed","description":"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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H","score":4.7},"cwes":["CWE-362"],"references":["https://git.kernel.org/stable/c/7466ae2aeed483de80c5d8dea0913cf74038b652","https://git.kernel.org/stable/c/869c63d5975d55e97f6b168e885452b3da20ea47","https://git.kernel.org/stable/c/e67299e1044349ad0088d52c6bc5764cc1816c06"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-19T22:28:18.033120106+00:00"},"epss":{"cve":"CVE-2026-23342","score":0.00091,"percentile":0.00459,"date":"2026-11-01"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}