Описание
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.
A flaw was found in the Linux kernel's Berkeley Packet Filter (BPF) memory allocator. A race condition occurs when bulk memory allocation and memory cleanup run concurrently without adequate synchronization. A local attacker could exploit this flaw to trigger a use-after-free condition, leading to a Denial of Service (DoS) via a system crash or potential privilege escalation.
Отчет
A race in the BPF memory allocator allows alloc_bulk to consume waiting_for_gp_ttrace while an RCU Tasks Trace callback removes and frees the same list. The confirmed result is a use-after-free read of entry next in llist_del_first, which can cause a kernel crash and may propagate stale list state if the freed node is reused before the read. A related race can affect free_by_rcu_ttrace during allocator draining when IRQ work and cross-CPU frees overlap. For the CVSS the PR:L value is used because a local user or process with access to the BPF interface may create the required allocation and free activity. Systems that disable unprivileged BPF may require CAP_BPF or equivalent capabilities and therefore have lower practical exposure. AC:H is used because successful triggering depends on a concurrent timing window involving RCU callbacks and list consumption. The issue is not directly network reachable. Impact is at least a local denial of service via kernel crash and in the paranoid case may include confidentiality and integrity impact due to reuse of a freed list node and possible allocator state corruption. Privilege escalation is plausible as a worst-case consequence of the memory corruption class but is not demonstrated by the available evidence.
Меры по смягчению последствий
Mitigation for this issue is either not available or the currently available options don't meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.
Затронутые пакеты
| Платформа | Пакет | Состояние | Рекомендация | Релиз |
|---|---|---|---|---|
| Red Hat Enterprise Linux 10 | kernel | Fix deferred | ||
| Red Hat Enterprise Linux 6 | kernel | Not affected | ||
| Red Hat Enterprise Linux 7 | kernel | Not affected | ||
| Red Hat Enterprise Linux 7 | kernel-rt | Not affected | ||
| Red Hat Enterprise Linux 8 | kernel | Not affected | ||
| Red Hat Enterprise Linux 8 | kernel-rt | Not affected | ||
| Red Hat Enterprise Linux 9 | kernel | Fix deferred | ||
| Red Hat Enterprise Linux 9 | kernel-rt | Not affected | ||
| Red Hat OpenShift Container Platform 4 | openshift/ose-rhel-coreos-8 | Not affected | ||
| Red Hat OpenShift Container Platform 4 | openshift/ose-rhel-coreos-9 | Fix deferred |
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Дополнительная информация
Статус:
4.7 Medium
CVSS3
Связанные уязвимости
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 ...
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_al
bpf: Fix UAF due to concurrent consumption of ttrace lists in alloc_bulk
In the Linux kernel, the following vulnerability has been resolved: b ...
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...
4.7 Medium
CVSS3