{
  "cveId": "CVE-2026-98642",
  "url": "https://patchblox.com/security/cve/CVE-2026-98642",
  "summary": "CVE-2026-98642 is fixed in 39 products on 1 platform, first by DEBIAN-CVE-2026-98642, released October 19, 2026. It is not reported as exploited. Patch Radar priority: Routine.",
  "title": "bpf: Fix UAF due to concurrent consumption of ttrace lists in alloc_bulk",
  "description": "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\u002B0x85/0x110 lib/llist.c:61 Read of size 8 at addr ffff8881572cd080 by task syz.4.470/5112  ...  llist_del_first\u002B0x85/0x110 lib/llist.c:61  alloc_bulk\u002B0x193/0x460 kernel/bpf/memalloc.c:229  bpf_mem_refill\u002B0x386/0x560 kernel/bpf/memalloc.c:436  Freed by task 14:  ...  __free_rcu kernel/bpf/memalloc.c:281 [inline]  __free_rcu_tasks_trace\u002B0x48/0xd0 kernel/bpf/memalloc.c:291  rcu_tasks_invoke_cbs\u002B0x1ec/0x3e0 kernel/rcu/tasks.h:571  rcu_tasks_one_gp\u002B0x13d/0x220 kernel/rcu/tasks.h:621  rcu_tasks_kthread\u002B0xf3/0x120 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(\u0026c-\u003Ewaiting_for_gp_ttrace)     entry = smp_load_acquire(\u0026head-\u003Efirst);     do {       if (entry == NULL)         return NULL;                                                free_all(llist_del_all(\u0026c-\u003Ewaiting_for_gp_ttrace))                                                  llist_for_each_safe(pos, t, llnode)                                                    free_one(pos);       next = READ_ONCE(entry-\u003Enext); \u003C-- trigger UAF     } while (!try_cmpxchg(\u0026head-\u003Efirst, \u0026entry, 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-\u003Ecall_rcu_ttrace_in_progress == 1, and concurrent cross-CPU frees repopulating c-\u003Efree_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(\u0026c-\u003Efree_by_rcu_ttrace)     entry = smp_load_acquire(\u0026head-\u003Efirst);     do {       if (entry == NULL)         return NULL;          // CPU1         bpf_mem_alloc_destroy()           WRITE_ONCE(c-\u003Edraining, true)           // wait for CPU0           irq_work_sync()                  // CPU2                 do_call_rcu_ttrace(tgt(CPU0))                   if (c-\u003Edraining) {                     llist_del_all(\u0026c-\u003Efree_by_rcu_ttrace)                     free_all()                   }  // CPU0 continue       next = READ_ONCE(entry-\u003Enext); \u003C-- trigger UAF     while (!try_cmpxchg(\u0026head-\u003Efirst, \u0026entry, next));  Fix this by introducing a raw spinlock to synchronize the concurrent consumption on waiting_for_gp_ttrace and free_by_rcu_ttrace.",
  "published": "2026-10-18T16:17:17Z",
  "severity": "Moderate",
  "cvss": 6.4,
  "epss": 0.00168,
  "epssPercentile": 0.06129,
  "priority": "Routine",
  "priorityTier": 4,
  "exploited": false,
  "vendorExploited": false,
  "disclosed": false,
  "vendorAdvisory": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-98642",
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      "fix": "ALAS2023-2026-3335",
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      "released": "2026-11-07T01:06:52Z"
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