{"id":"DEBIAN-CVE-2026-98642","details":"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-\u003ewaiting_for_gp_ttrace)     entry = smp_load_acquire(&head-\u003efirst);     do {       if (entry == NULL)         return NULL;                                                free_all(llist_del_all(&c-\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(&head-\u003efirst, &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-\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(&c-\u003efree_by_rcu_ttrace)     entry = smp_load_acquire(&head-\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(&c-\u003efree_by_rcu_ttrace)                     free_all()                   }  // CPU0 continue       next = READ_ONCE(entry-\u003enext); \u003c-- trigger UAF     while (!try_cmpxchg(&head-\u003efirst, &entry, next));  Fix this by introducing a raw spinlock to synchronize the concurrent consumption on waiting_for_gp_ttrace and free_by_rcu_ttrace.","modified":"2026-10-19T05:00:29.581010897Z","published":"2026-10-18T17:47:40.021712473Z","upstream":["CVE-2026-98642"],"references":[{"type":"ADVISORY","url":"https://security-tracker.debian.org/tracker/CVE-2026-98642"}],"affected":[{"package":{"name":"linux","ecosystem":"Debian:13","purl":"pkg:deb/debian/linux?arch=source&distro=trixie"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.12.113-1"}]}],"versions":["6.12.100-1","6.12.101-1","6.12.105-1","6.12.107-1","6.12.111-1","6.12.38-1","6.12.41-1","6.12.43-1","6.12.43-1~bpo12+1","6.12.48-1","6.12.57-1","6.12.57-1~bpo12+1","6.12.63-1","6.12.63-1~bpo12+1","6.12.69-1","6.12.69-1~bpo12+1","6.12.73-1","6.12.73-1~bpo12+1","6.12.74-1","6.12.74-2","6.12.74-2~bpo12+1","6.12.85-1","6.12.85-1~bpo12+1","6.12.86-1","6.12.86-1~bpo12+1","6.12.88-1","6.12.88-1~bpo12+1","6.12.90-1","6.12.90-1~bpo12+1","6.12.90-2","6.12.90-2~bpo12+1","6.12.94-1","6.12.94-1~bpo12+1","6.12.95-1","6.12.95-1~bpo12+1","6.12.96-1"],"ecosystem_specific":{"urgency":"not 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