CVE-2026-23342

// Conceptual PoC for CVE-2026-23342 // Triggering the race condition in Linux Kernel BPF cpumap on PREEMPT_RT // Note: Actual reproduction requires a specific kernel config and syzkaller-like setup. #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <pthread.h> // Simulate the operations that lead to the race void* task_a(void* arg) { // Simulates __cpu_map_flush -> bq_flush_to_queue // The critical section where bq->count is reset printf("Task A: Starting flush...\n"); usleep(100); // Simulate delay to force preemption window printf("Task A: Attempting list delete (potential crash)\n"); return NULL; } void* task_b(void* arg) { // Simulates bq_enqueue -> bq_flush_to_queue // Runs concurrently on the same CPU due to PREEMPT_RT printf("Task B: Enqueuing packets...\n"); printf("Task B: Triggering flush and list delete\n"); return NULL; } int main() { pthread_t t1, t2; printf("Starting PoC for CVE-2026-23342 (Race Condition)\n"); pthread_create(&t1, NULL, task_a, NULL); pthread_create(&t2, NULL, task_b, NULL); pthread_join(t1, NULL); pthread_join(t2, NULL); return 0; }

{"cve": {"id": "CVE-2026-23342", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-03-25T11:16:32.147", "lastModified": "2026-04-23T21:16:19.007", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "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."}, {"lang": "es", "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-&gt;count se reinicia en bq_flush_to_queue(), una tarea preemptora puede llamar a bq_enqueue() -&gt; bq_flush_to_queue() en la misma bq cuando bq-&gt;count alcanza CPU_MAP_BULK_SIZE. Ambas tareas luego llaman a __list_del_clearprev() en el mismo bq-&gt;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-&gt;count y bq-&gt;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 -&gt; bq_flush_to_queue) y la tarea B (bq_enqueue -&gt; bq_flush_to_queue) en la misma CPU:\n\n Tarea A (xdp_do_flush) Tarea B (cpu_map_enqueue)\n ---------------------- ------------------------\n b ... (truncated)