{"id":"CVE-2026-23294","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-23294","generatedAt":"2026-10-28T09:26:42.761Z","title":"In the Linux kernel, the following vulnerability has been resolved: bpf: Fix race in devmap on PREEMPT_RT On PREEMPT_RT kernels, the per-CPU xdp_dev_bulk_queue (bq) can be accessed concurrently by multiple preemptible tasks on the same CPU.","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":"2026-03-25T11:16:25.000Z","lastModified":"2026-06-17T10:21:16.000Z","status":"Analyzed","sourceIdentifier":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","cvss":{"version":"3.1","score":7,"severity":"HIGH","vector":"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H"},"cwe":["CWE-362"],"affected":["linux/linux kernel"],"epss":{"score":0.00094,"percentile":0.00564,"date":"2026-10-27","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"high","text":"High impact if exploited, but EPSS currently rates exploitation as unlikely (0.09%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit."},"changes":[],"references":[{"url":"https://git.kernel.org/stable/c/1872e75375c40add4a35990de3be77b5741c252c","tags":["Patch"],"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/6c10b019785dc282c5f45d21e4a3f468b8fd6476","tags":["Patch"],"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/ab1a56c9d99189aa5c6e03940d06e40ba6a28240","tags":["Patch"],"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-23294","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}