CVE-2026-98642 (GCVE-0-2026-98642)

Vulnerability from cvelistv5 – Published: 2026-10-18 15:20 – Updated: 2026-10-19 09:23
VLAI
Title
bpf: Fix UAF due to concurrent consumption of ttrace lists in alloc_bulk
Summary
In the Linux kernel, the following vulnerability has been resolved: bpf: Fix UAF due to concurrent consumption of ttrace lists in alloc_bulk Syzkaller repeatedly triggered UAF splats related to nodes in waiting_for_gp_ttrace within the bpf memalloc: BUG: KASAN: slab-use-after-free in llist_del_first+0x85/0x110 lib/llist.c:61 Read of size 8 at addr ffff8881572cd080 by task syz.4.470/5112 ... llist_del_first+0x85/0x110 lib/llist.c:61 alloc_bulk+0x193/0x460 kernel/bpf/memalloc.c:229 bpf_mem_refill+0x386/0x560 kernel/bpf/memalloc.c:436 Freed by task 14: ... __free_rcu kernel/bpf/memalloc.c:281 [inline] __free_rcu_tasks_trace+0x48/0xd0 kernel/bpf/memalloc.c:291 rcu_tasks_invoke_cbs+0x1ec/0x3e0 kernel/rcu/tasks.h:571 rcu_tasks_one_gp+0x13d/0x220 kernel/rcu/tasks.h:621 rcu_tasks_kthread+0xf3/0x120 kernel/rcu/tasks.h:651 The reason is that the UAF occurs after the RCU Tasks Trace GP expires: when the __free_rcu() callback runs, there is no synchronization protecting llist_del_all() against concurrent alloc_bulk() operating on waiting_for_gp_ttrace, leading to the race condition below: CPU0 CPU1 __free_rcu (RCU Tasks Trace callback) alloc_bulk llist_del_first(&c->waiting_for_gp_ttrace) entry = smp_load_acquire(&head->first); do { if (entry == NULL) return NULL; free_all(llist_del_all(&c->waiting_for_gp_ttrace)) llist_for_each_safe(pos, t, llnode) free_one(pos); next = READ_ONCE(entry->next); <-- trigger UAF } while (!try_cmpxchg(&head->first, &entry, next)); In addition, there is also a theoretical race condition on the free_by_rcu_ttrace list. This race requires two preconditions: an in-flight Tasks Trace GP keeping c->call_rcu_ttrace_in_progress == 1, and concurrent cross-CPU frees repopulating c->free_by_rcu_ttrace with new nodes. Under these conditions, the following scenario triggers UAF: // CPU0 // irq work is still busy (on PREEMPT_RT) alloc_bulk() llist_del_first(&c->free_by_rcu_ttrace) entry = smp_load_acquire(&head->first); do { if (entry == NULL) return NULL; // CPU1 bpf_mem_alloc_destroy() WRITE_ONCE(c->draining, true) // wait for CPU0 irq_work_sync() // CPU2 do_call_rcu_ttrace(tgt(CPU0)) if (c->draining) { llist_del_all(&c->free_by_rcu_ttrace) free_all() } // CPU0 continue next = READ_ONCE(entry->next); <-- trigger UAF while (!try_cmpxchg(&head->first, &entry, next)); Fix this by introducing a raw spinlock to synchronize the concurrent consumption on waiting_for_gp_ttrace and free_by_rcu_ttrace.
Severity
No CVSS data available.
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 7018 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 04fabf00b4d3aff5d010ecb617001814e409e24a , < a0e150a118025a05c8662c536ba2a865da86419c (git)
Affected: 04fabf00b4d3aff5d010ecb617001814e409e24a , < 1d6581b544a88cf4348c2fb60dcb50ad63f012da (git)
Affected: 04fabf00b4d3aff5d010ecb617001814e409e24a , < f101602415fb39a58941bec444df65634d5a6844 (git)
Affected: 04fabf00b4d3aff5d010ecb617001814e409e24a , < 1c21452d02eec2f008e2c5535820f85adbd7587a (git)
guessed Create a notification for this product.
Linux Linux Affected: 6.6
Unaffected: 0 , < 6.6 (semver)
Unaffected: 6.12.112 , ≤ 6.12.* (semver)
Unaffected: 6.18.55 , ≤ 6.18.* (semver)
Unaffected: 7.2.9 , ≤ 7.2.* (semver)
Unaffected: 7.3 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
Show details on NVD website
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          "product": "Linux",
          "programFiles": [
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          "vendor": "Linux",
          "versions": [
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              "versionType": "semver"
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              "versionType": "semver"
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                {
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          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix UAF due to concurrent consumption of ttrace lists in alloc_bulk\n\nSyzkaller repeatedly triggered UAF splats related to nodes in\nwaiting_for_gp_ttrace within the bpf memalloc:\n\nBUG: KASAN: slab-use-after-free in llist_del_first+0x85/0x110 lib/llist.c:61\nRead of size 8 at addr ffff8881572cd080 by task syz.4.470/5112\n ...\n llist_del_first+0x85/0x110 lib/llist.c:61\n alloc_bulk+0x193/0x460 kernel/bpf/memalloc.c:229\n bpf_mem_refill+0x386/0x560 kernel/bpf/memalloc.c:436\n\nFreed by task 14:\n ...\n __free_rcu kernel/bpf/memalloc.c:281 [inline]\n __free_rcu_tasks_trace+0x48/0xd0 kernel/bpf/memalloc.c:291\n rcu_tasks_invoke_cbs+0x1ec/0x3e0 kernel/rcu/tasks.h:571\n rcu_tasks_one_gp+0x13d/0x220 kernel/rcu/tasks.h:621\n rcu_tasks_kthread+0xf3/0x120 kernel/rcu/tasks.h:651\n\nThe reason is that the UAF occurs after the RCU Tasks Trace GP expires:\nwhen the __free_rcu() callback runs, there is no synchronization\nprotecting llist_del_all() against concurrent alloc_bulk() operating on\nwaiting_for_gp_ttrace, leading to the race condition below:\n\nCPU0                                           CPU1\n                                               __free_rcu (RCU Tasks Trace callback)\nalloc_bulk\n  llist_del_first(\u0026c-\u003ewaiting_for_gp_ttrace)\n    entry = smp_load_acquire(\u0026head-\u003efirst);\n    do {\n      if (entry == NULL)\n        return NULL;\n                                               free_all(llist_del_all(\u0026c-\u003ewaiting_for_gp_ttrace))\n                                                 llist_for_each_safe(pos, t, llnode)\n                                                   free_one(pos);\n      next = READ_ONCE(entry-\u003enext); \u003c-- trigger UAF\n    } while (!try_cmpxchg(\u0026head-\u003efirst, \u0026entry, next));\n\nIn addition, there is also a theoretical race condition on the\nfree_by_rcu_ttrace list. This race requires two preconditions: an\nin-flight Tasks Trace GP keeping c-\u003ecall_rcu_ttrace_in_progress == 1,\nand concurrent cross-CPU frees repopulating c-\u003efree_by_rcu_ttrace with\nnew nodes. Under these conditions, the following scenario triggers UAF:\n\n// CPU0\n// irq work is still busy (on PREEMPT_RT)\nalloc_bulk()\n  llist_del_first(\u0026c-\u003efree_by_rcu_ttrace)\n    entry = smp_load_acquire(\u0026head-\u003efirst);\n    do {\n      if (entry == NULL)\n        return NULL;\n\n        // CPU1\n        bpf_mem_alloc_destroy()\n          WRITE_ONCE(c-\u003edraining, true)\n          // wait for CPU0\n          irq_work_sync()\n\n                // CPU2\n                do_call_rcu_ttrace(tgt(CPU0))\n                  if (c-\u003edraining) {\n                    llist_del_all(\u0026c-\u003efree_by_rcu_ttrace)\n                    free_all()\n                  }\n\n// CPU0 continue\n      next = READ_ONCE(entry-\u003enext); \u003c-- trigger UAF\n    while (!try_cmpxchg(\u0026head-\u003efirst, \u0026entry, next));\n\nFix this by introducing a raw spinlock to synchronize the concurrent\nconsumption on waiting_for_gp_ttrace and free_by_rcu_ttrace."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T09:23:11.995Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
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          "url": "https://git.kernel.org/stable/c/a0e150a118025a05c8662c536ba2a865da86419c"
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          "url": "https://git.kernel.org/stable/c/1d6581b544a88cf4348c2fb60dcb50ad63f012da"
        },
        {
          "url": "https://git.kernel.org/stable/c/f101602415fb39a58941bec444df65634d5a6844"
        },
        {
          "url": "https://git.kernel.org/stable/c/1c21452d02eec2f008e2c5535820f85adbd7587a"
        }
      ],
      "title": "bpf: Fix UAF due to concurrent consumption of ttrace lists in alloc_bulk",
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  "cveMetadata": {
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98642",
    "datePublished": "2026-10-18T15:20:13.740Z",
    "dateReserved": "2026-09-25T10:25:14.361Z",
    "dateUpdated": "2026-10-19T09:23:11.995Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-98642",
      "date": "2026-11-01",
      "epss": "0.00168",
      "percentile": "0.06071"
    },
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      "current_release_date": "2026-10-21T18:38:56.000Z",
      "cve": "CVE-2026-98642",
      "id": "msrc_CVE-2026-98642",
      "initial_release_date": "2026-10-20T01:07:08.000Z",
      "product_status:known_affected": "1",
      "product_status:under_investigation": "1",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "bpf: Fix UAF due to concurrent consumption of ttrace lists in alloc_bulk",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-98642.json",
      "version": "2"
    },
    "nvd": {
      "cve": {
        "affected": [
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                "defaultStatus": "unaffected",
                "product": "Linux",
                "programFiles": [
                  "kernel/bpf/memalloc.c"
                ],
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                "vendor": "Linux",
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                "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                "vendor": "Linux",
                "versions": [
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                    "versionType": "semver"
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                    "versionType": "semver"
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                  {
                    "lessThanOrEqual": "6.18.*",
                    "status": "unaffected",
                    "version": "6.18.55",
                    "versionType": "semver"
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                    "versionType": "semver"
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          }
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        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix UAF due to concurrent consumption of ttrace lists in alloc_bulk\n\nSyzkaller repeatedly triggered UAF splats related to nodes in\nwaiting_for_gp_ttrace within the bpf memalloc:\n\nBUG: KASAN: slab-use-after-free in llist_del_first+0x85/0x110 lib/llist.c:61\nRead of size 8 at addr ffff8881572cd080 by task syz.4.470/5112\n ...\n llist_del_first+0x85/0x110 lib/llist.c:61\n alloc_bulk+0x193/0x460 kernel/bpf/memalloc.c:229\n bpf_mem_refill+0x386/0x560 kernel/bpf/memalloc.c:436\n\nFreed by task 14:\n ...\n __free_rcu kernel/bpf/memalloc.c:281 [inline]\n __free_rcu_tasks_trace+0x48/0xd0 kernel/bpf/memalloc.c:291\n rcu_tasks_invoke_cbs+0x1ec/0x3e0 kernel/rcu/tasks.h:571\n rcu_tasks_one_gp+0x13d/0x220 kernel/rcu/tasks.h:621\n rcu_tasks_kthread+0xf3/0x120 kernel/rcu/tasks.h:651\n\nThe reason is that the UAF occurs after the RCU Tasks Trace GP expires:\nwhen the __free_rcu() callback runs, there is no synchronization\nprotecting llist_del_all() against concurrent alloc_bulk() operating on\nwaiting_for_gp_ttrace, leading to the race condition below:\n\nCPU0                                           CPU1\n                                               __free_rcu (RCU Tasks Trace callback)\nalloc_bulk\n  llist_del_first(\u0026c-\u003ewaiting_for_gp_ttrace)\n    entry = smp_load_acquire(\u0026head-\u003efirst);\n    do {\n      if (entry == NULL)\n        return NULL;\n                                               free_all(llist_del_all(\u0026c-\u003ewaiting_for_gp_ttrace))\n                                                 llist_for_each_safe(pos, t, llnode)\n                                                   free_one(pos);\n      next = READ_ONCE(entry-\u003enext); \u003c-- trigger UAF\n    } while (!try_cmpxchg(\u0026head-\u003efirst, \u0026entry, next));\n\nIn addition, there is also a theoretical race condition on the\nfree_by_rcu_ttrace list. This race requires two preconditions: an\nin-flight Tasks Trace GP keeping c-\u003ecall_rcu_ttrace_in_progress == 1,\nand concurrent cross-CPU frees repopulating c-\u003efree_by_rcu_ttrace with\nnew nodes. Under these conditions, the following scenario triggers UAF:\n\n// CPU0\n// irq work is still busy (on PREEMPT_RT)\nalloc_bulk()\n  llist_del_first(\u0026c-\u003efree_by_rcu_ttrace)\n    entry = smp_load_acquire(\u0026head-\u003efirst);\n    do {\n      if (entry == NULL)\n        return NULL;\n\n        // CPU1\n        bpf_mem_alloc_destroy()\n          WRITE_ONCE(c-\u003edraining, true)\n          // wait for CPU0\n          irq_work_sync()\n\n                // CPU2\n                do_call_rcu_ttrace(tgt(CPU0))\n                  if (c-\u003edraining) {\n                    llist_del_all(\u0026c-\u003efree_by_rcu_ttrace)\n                    free_all()\n                  }\n\n// CPU0 continue\n      next = READ_ONCE(entry-\u003enext); \u003c-- trigger UAF\n    while (!try_cmpxchg(\u0026head-\u003efirst, \u0026entry, next));\n\nFix this by introducing a raw spinlock to synchronize the concurrent\nconsumption on waiting_for_gp_ttrace and free_by_rcu_ttrace."
          }
        ],
        "id": "CVE-2026-98642",
        "lastModified": "2026-10-19T10:19:28.443",
        "metrics": {},
        "published": "2026-10-18T16:17:17.367",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/1c21452d02eec2f008e2c5535820f85adbd7587a"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/1d6581b544a88cf4348c2fb60dcb50ad63f012da"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/a0e150a118025a05c8662c536ba2a865da86419c"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/f101602415fb39a58941bec444df65634d5a6844"
          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-10-21T19:41:51+00:00",
      "cve": "CVE-2026-98642",
      "id": "CVE-2026-98642",
      "initial_release_date": "2026-10-18T00:00:00+00:00",
      "product_status:known_affected": "185",
      "product_status:known_not_affected": "93",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: bpf: Fix UAF due to concurrent consumption of ttrace lists in alloc_bulk",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-98642.json",
      "version": "3"
    }
  }
}



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