{"id":"CVE-2026-98642","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:\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…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 04fabf00b4d3aff5d010ecb617001814e409e24a < a0e150a118025a05c8662c536ba2a865da86419c","Linux >= 04fabf00b4d3aff5d010ecb617001814e409e24a < 1d6581b544a88cf4348c2fb60dcb50ad63f012da","Linux >= 04fabf00b4d3aff5d010ecb617001814e409e24a < f101602415fb39a58941bec444df65634d5a6844","Linux >= 04fabf00b4d3aff5d010ecb617001814e409e24a < 1c21452d02eec2f008e2c5535820f85adbd7587a","Linux 6.6"],"published":"2026-10-18","updated":"2026-10-18","sourceUpdated":"2026-10-18T15:20:13.740Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-98642","references":[{"url":"https://git.kernel.org/stable/c/a0e150a118025a05c8662c536ba2a865da86419c"},{"url":"https://git.kernel.org/stable/c/1d6581b544a88cf4348c2fb60dcb50ad63f012da"},{"url":"https://git.kernel.org/stable/c/f101602415fb39a58941bec444df65634d5a6844"},{"url":"https://git.kernel.org/stable/c/1c21452d02eec2f008e2c5535820f85adbd7587a"}],"tags":["cve.org"],"ingestedAt":"2026-10-18T15:45:12.229Z","slug":"CVE-2026-98642","body":"## Overview\n\nIn 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(&c->waiting_for_gp_ttrace)\n    entry = smp_load_acquire(&head->first);\n    do {\n      if (entry == NULL)\n        return NULL;\n                                               free_all(llist_del_all(&c->waiting_for_gp_ttrace))\n                                                 llist_for_each_safe(pos, t, llnode)\n                                                   free_one(pos);\n      next = READ_ONCE(entry->next); <-- trigger UAF\n    } while (!try_cmpxchg(&head->first, &entry, 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->call_rcu_ttrace_in_progress == 1,\nand concurrent cross-CPU frees repopulating c->free_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(&c->free_by_rcu_ttrace)\n    entry = smp_load_acquire(&head->first);\n    do {\n      if (entry == NULL)\n        return NULL;\n\n        // CPU1\n        bpf_mem_alloc_destroy()\n          WRITE_ONCE(c->draining, true)\n          // wait for CPU0\n          irq_work_sync()\n\n                // CPU2\n                do_call_rcu_ttrace(tgt(CPU0))\n                  if (c->draining) {\n                    llist_del_all(&c->free_by_rcu_ttrace)\n                    free_all()\n                  }\n\n// CPU0 continue\n      next = READ_ONCE(entry->next); <-- trigger UAF\n    while (!try_cmpxchg(&head->first, &entry, next));\n\nFix this by introducing a raw spinlock to synchronize the concurrent\nconsumption on waiting_for_gp_ttrace and free_by_rcu_ttrace.\n\n## Affected\n\n- `Linux >= 04fabf00b4d3aff5d010ecb617001814e409e24a < a0e150a118025a05c8662c536ba2a865da86419c`\n- `Linux >= 04fabf00b4d3aff5d010ecb617001814e409e24a < 1d6581b544a88cf4348c2fb60dcb50ad63f012da`\n- `Linux >= 04fabf00b4d3aff5d010ecb617001814e409e24a < f101602415fb39a58941bec444df65634d5a6844`\n- `Linux >= 04fabf00b4d3aff5d010ecb617001814e409e24a < 1c21452d02eec2f008e2c5535820f85adbd7587a`\n- `Linux 6.6`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}