CVE-2026-23342
Estado: AnalizadaMedia (4.7)—
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.
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This leads to several races:
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:
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.
Detalles técnicos trazas, registros y código del informe original
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.
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 */CVSS
- Versión: 3.1
- Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
- Puntuación base: 4.7
Probabilidad de explotación (EPSS)
- Probabilidad de explotación en los próximos 30 días: 0.09%
- Percentil entre todas las CVEs puntuadas: 0
- Fecha de la puntuación: 5/10/2026
EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).
Tecnologías afectadas (1)
CWE
- CWE-362
Referencias
JSON original (NVD)
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"vectorString": "CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H",
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"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->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."
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"value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\nbpf: Corrige condición de carrera en cpumap en PREEMPT_RT\n\nEn kernels PREEMPT_RT, la xdp_bulk_queue (bq) por CPU puede ser accedida concurrentemente por múltiples tareas preemptibles en la misma CPU.\n\nEl código original asume que bq_enqueue() y __cpu_map_flush() se ejecutan atómicamente una con respecto a la otra en la misma CPU, confiando en local_bh_disable() para prevenir la preemption. Sin embargo, en PREEMPT_RT, local_bh_disable() solo llama a migrate_disable() (cuando PREEMPT_RT_NEEDS_BH_LOCK no está configurado) y no deshabilita la preemption, lo que permite que la planificación CFS preempte una tarea durante bq_flush_to_queue(), permitiendo que otra tarea en la misma CPU entre en bq_enqueue() y opere en la misma bq por CPU concurrentemente.\n\nEsto conduce a varias condiciones de carrera:\n\n1. Doble __list_del_clearprev(): después de que bq->count se reinicia en bq_flush_to_queue(), una tarea preemptora puede llamar a bq_enqueue() -> bq_flush_to_queue() en la misma bq cuando bq->count alcanza CPU_MAP_BULK_SIZE. Ambas tareas luego llaman a __list_del_clearprev() en el mismo bq->flush_node, la segunda llamada desreferencia el puntero prev que ya había sido establecido a NULL por la primera.\n\n2. Condiciones de carrera de bq->count y bq->q[]: bq_enqueue() concurrente puede corromper la cola de paquetes mientras bq_flush_to_queue() la está procesando.\n\nLa condición de carrera entre la tarea A (__cpu_map_flush -> bq_flush_to_queue) y la tarea B (bq_enqueue -> bq_flush_to_queue) en la misma CPU:\n\n Tarea A (xdp_do_flush) Tarea B (cpu_map_enqueue)\n ---------------------- ------------------------\n bq_flush_to_queue(bq)\n spin_lock(&q->producer_lock)\n /* vaciar bq->q[] a ptr_ring */\n bq->count = 0\n spin_unlock(&q->producer_lock)\n bq_enqueue(rcpu, xdpf)\n <-- CFS preempte la Tarea A --> bq->q[bq->count++] = xdpf\n /* ... más encolamientos hasta llenarse ... */\n bq_flush_to_queue(bq)\n spin_lock(&q->producer_lock)\n /* vaciar a ptr_ring */\n spin_unlock(&q->producer_lock)\n __list_del_clearprev(flush_node)\n /* establece flush_node.prev = NULL */\n <-- La Tarea A se reanuda -->\n __list_del_clearprev(flush_node)\n flush_node.prev->next = ...\n /* prev es NULL -> kernel oops */\n\nSolucione esto añadiendo un local_lock_t a xdp_bulk_queue y adquiriéndolo en bq_enqueue() y __cpu_map_flush(). Estas rutas ya se ejecutan bajo local_bh_disable(), por lo que se usa local_lock_nested_bh() que en sistemas no-RT es una anotación pura sin sobrecarga, y en PREEMPT_RT proporciona un bloqueo de suspensión por CPU que serializa el acceso a la bq.\n\nPara reproducir, inserte un mdelay(100) entre bq->count = 0 y __list_del_clearprev() en bq_flush_to_queue(), luego ejecute el reproductor proporcionado por syzkaller."
}
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"lastModified": "2026-06-17T10:21:22.597",
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