CVE-2026-23342 (GCVE-0-2026-23342)
Vulnerability from cvelistv5 – Published: 2026-03-25 10:27 – Updated: 2026-04-13 06:05
VLAI?
Title
bpf: Fix race in cpumap on PREEMPT_RT
Summary
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.
This leads to several races:
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.
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:
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 */
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.
Severity ?
No CVSS data available.
Assigner
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| Linux | Linux |
Affected:
3253cb49cbad4772389d6ef55be75db1f97da910 , < 7466ae2aeed483de80c5d8dea0913cf74038b652
(git)
Affected: 3253cb49cbad4772389d6ef55be75db1f97da910 , < e67299e1044349ad0088d52c6bc5764cc1816c06 (git) Affected: 3253cb49cbad4772389d6ef55be75db1f97da910 , < 869c63d5975d55e97f6b168e885452b3da20ea47 (git) |
||
{
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"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-\u003ecount is reset in\n bq_flush_to_queue(), a preempting task can call bq_enqueue() -\u003e\n bq_flush_to_queue() on the same bq when bq-\u003ecount reaches\n CPU_MAP_BULK_SIZE. Both tasks then call __list_del_clearprev()\n on the same bq-\u003eflush_node, the second call dereferences the\n prev pointer that was already set to NULL by the first.\n\n2. bq-\u003ecount and bq-\u003eq[] 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 -\u003e bq_flush_to_queue) and\ntask B (bq_enqueue -\u003e 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(\u0026q-\u003eproducer_lock)\n /* flush bq-\u003eq[] to ptr_ring */\n bq-\u003ecount = 0\n spin_unlock(\u0026q-\u003eproducer_lock)\n bq_enqueue(rcpu, xdpf)\n \u003c-- CFS preempts Task A --\u003e bq-\u003eq[bq-\u003ecount++] = xdpf\n /* ... more enqueues until full ... */\n bq_flush_to_queue(bq)\n spin_lock(\u0026q-\u003eproducer_lock)\n /* flush to ptr_ring */\n spin_unlock(\u0026q-\u003eproducer_lock)\n __list_del_clearprev(flush_node)\n /* sets flush_node.prev = NULL */\n \u003c-- Task A resumes --\u003e\n __list_del_clearprev(flush_node)\n flush_node.prev-\u003enext = ...\n /* prev is NULL -\u003e 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-\u003ecount = 0 and\n__list_del_clearprev() in bq_flush_to_queue(), then run reproducer\nprovided by syzkaller."
}
],
"providerMetadata": {
"dateUpdated": "2026-04-13T06:05:24.834Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"references": [
{
"url": "https://git.kernel.org/stable/c/7466ae2aeed483de80c5d8dea0913cf74038b652"
},
{
"url": "https://git.kernel.org/stable/c/e67299e1044349ad0088d52c6bc5764cc1816c06"
},
{
"url": "https://git.kernel.org/stable/c/869c63d5975d55e97f6b168e885452b3da20ea47"
}
],
"title": "bpf: Fix race in cpumap on PREEMPT_RT",
"x_generator": {
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}
}
},
"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2026-23342",
"datePublished": "2026-03-25T10:27:30.285Z",
"dateReserved": "2026-01-13T15:37:45.999Z",
"dateUpdated": "2026-04-13T06:05:24.834Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
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"vulnerability-lookup:meta": {
"epss": {
"cve": "CVE-2026-23342",
"date": "2026-04-24",
"epss": "0.00012",
"percentile": "0.017"
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"nvd": "{\"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-\u003ecount is reset in\\n bq_flush_to_queue(), a preempting task can call bq_enqueue() -\u003e\\n bq_flush_to_queue() on the same bq when bq-\u003ecount reaches\\n CPU_MAP_BULK_SIZE. Both tasks then call __list_del_clearprev()\\n on the same bq-\u003eflush_node, the second call dereferences the\\n prev pointer that was already set to NULL by the first.\\n\\n2. bq-\u003ecount and bq-\u003eq[] 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 -\u003e bq_flush_to_queue) and\\ntask B (bq_enqueue -\u003e 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(\u0026q-\u003eproducer_lock)\\n /* flush bq-\u003eq[] to ptr_ring */\\n bq-\u003ecount = 0\\n spin_unlock(\u0026q-\u003eproducer_lock)\\n bq_enqueue(rcpu, xdpf)\\n \u003c-- CFS preempts Task A --\u003e bq-\u003eq[bq-\u003ecount++] = xdpf\\n /* ... more enqueues until full ... */\\n bq_flush_to_queue(bq)\\n spin_lock(\u0026q-\u003eproducer_lock)\\n /* flush to ptr_ring */\\n spin_unlock(\u0026q-\u003eproducer_lock)\\n __list_del_clearprev(flush_node)\\n /* sets flush_node.prev = NULL */\\n \u003c-- Task A resumes --\u003e\\n __list_del_clearprev(flush_node)\\n flush_node.prev-\u003enext = ...\\n /* prev is NULL -\u003e 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-\u003ecount = 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 condici\u00f3n de carrera en cpumap en PREEMPT_RT\\n\\nEn kernels PREEMPT_RT, la xdp_bulk_queue (bq) por CPU puede ser accedida concurrentemente por m\u00faltiples tareas preemptibles en la misma CPU.\\n\\nEl c\u00f3digo original asume que bq_enqueue() y __cpu_map_flush() se ejecutan at\u00f3micamente 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 est\u00e1 configurado) y no deshabilita la preemption, lo que permite que la planificaci\u00f3n 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(): despu\u00e9s de que bq-\u0026gt;count se reinicia en bq_flush_to_queue(), una tarea preemptora puede llamar a bq_enqueue() -\u0026gt; bq_flush_to_queue() en la misma bq cuando bq-\u0026gt;count alcanza CPU_MAP_BULK_SIZE. Ambas tareas luego llaman a __list_del_clearprev() en el mismo bq-\u0026gt;flush_node, la segunda llamada desreferencia el puntero prev que ya hab\u00eda sido establecido a NULL por la primera.\\n\\n2. Condiciones de carrera de bq-\u0026gt;count y bq-\u0026gt;q[]: bq_enqueue() concurrente puede corromper la cola de paquetes mientras bq_flush_to_queue() la est\u00e1 procesando.\\n\\nLa condici\u00f3n de carrera entre la tarea A (__cpu_map_flush -\u0026gt; bq_flush_to_queue) y la tarea B (bq_enqueue -\u0026gt; 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(\u0026amp;q-\u0026gt;producer_lock)\\n /* vaciar bq-\u0026gt;q[] a ptr_ring */\\n bq-\u0026gt;count = 0\\n spin_unlock(\u0026amp;q-\u0026gt;producer_lock)\\n bq_enqueue(rcpu, xdpf)\\n \u0026lt;-- CFS preempte la Tarea A --\u0026gt; bq-\u0026gt;q[bq-\u0026gt;count++] = xdpf\\n /* ... m\u00e1s encolamientos hasta llenarse ... */\\n bq_flush_to_queue(bq)\\n spin_lock(\u0026amp;q-\u0026gt;producer_lock)\\n /* vaciar a ptr_ring */\\n spin_unlock(\u0026amp;q-\u0026gt;producer_lock)\\n __list_del_clearprev(flush_node)\\n /* establece flush_node.prev = NULL */\\n \u0026lt;-- La Tarea A se reanuda --\u0026gt;\\n __list_del_clearprev(flush_node)\\n flush_node.prev-\u0026gt;next = ...\\n /* prev es NULL -\u0026gt; kernel oops */\\n\\nSolucione esto a\u00f1adiendo un local_lock_t a xdp_bulk_queue y adquiri\u00e9ndolo 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 anotaci\u00f3n pura sin sobrecarga, y en PREEMPT_RT proporciona un bloqueo de suspensi\u00f3n por CPU que serializa el acceso a la bq.\\n\\nPara reproducir, inserte un mdelay(100) entre bq-\u0026gt;count = 0 y __list_del_clearprev() en bq_flush_to_queue(), luego ejecute el reproductor proporcionado por syzkaller.\"}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"nvd@nist.gov\",\"type\":\"Primary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H\",\"baseScore\":4.7,\"baseSeverity\":\"MEDIUM\",\"attackVector\":\"LOCAL\",\"attackComplexity\":\"HIGH\",\"privilegesRequired\":\"LOW\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"NONE\",\"integrityImpact\":\"NONE\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":1.0,\"impactScore\":3.6}]},\"weaknesses\":[{\"source\":\"nvd@nist.gov\",\"type\":\"Primary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-362\"}]}],\"configurations\":[{\"nodes\":[{\"operator\":\"OR\",\"negate\":false,\"cpeMatch\":[{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"6.18.1\",\"versionEndExcluding\":\"6.18.17\",\"matchCriteriaId\":\"07E9D8CD-82F0-4CC6-8038-BF71758D583C\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"6.19\",\"versionEndExcluding\":\"6.19.7\",\"matchCriteriaId\":\"69245D10-0B71-485E-80C3-A64F077004D3\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:6.18:-:*:*:*:*:*:*\",\"matchCriteriaId\":\"DCE57113-2223-4308-A0F2-5E6ECFBB3C23\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:*\",\"matchCriteriaId\":\"F253B622-8837-4245-BCE5-A7BF8FC76A16\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:7.0:rc2:*:*:*:*:*:*\",\"matchCriteriaId\":\"4AE85AD8-4641-4E7C-A2F4-305E2CD9EE64\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:7.0:rc3:*:*:*:*:*:*\",\"matchCriteriaId\":\"F666C8D8-6538-46D4-B318-87610DE64C34\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:7.0:rc4:*:*:*:*:*:*\",\"matchCriteriaId\":\"02259FDA-961B-47BC-AE7F-93D7EC6E90C2\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:7.0:rc5:*:*:*:*:*:*\",\"matchCriteriaId\":\"58A9FEFF-C040-420D-8F0A-BFDAAA1DF258\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:7.0:rc6:*:*:*:*:*:*\",\"matchCriteriaId\":\"1D2315C0-D46F-4F85-9754-F9E5E11374A6\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:7.0:rc7:*:*:*:*:*:*\",\"matchCriteriaId\":\"512EE3A8-A590-4501-9A94-5D4B268D6138\"}]}]}],\"references\":[{\"url\":\"https://git.kernel.org/stable/c/7466ae2aeed483de80c5d8dea0913cf74038b652\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/869c63d5975d55e97f6b168e885452b3da20ea47\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/e67299e1044349ad0088d52c6bc5764cc1816c06\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]}]}}"
}
}
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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