CVE-2025-39886

In the Linux kernel, the following vulnerability has been resolved:

bpf: Tell memcg to use allow_spinning=false path in bpf_timer_init()

Currently, calling bpf_map_kmalloc_node() from __bpf_async_init() can

cause various locking issues; see the following stack trace (edited for

style) as one example:

...

[10.011566] do_raw_spin_lock.cold

[10.011570] try_to_wake_up (5) double-acquiring the same

[10.011575] kick_pool rq_lock, causing a hardlockup

[10.011579] __queue_work

[10.011582] queue_work_on

[10.011585] kernfs_notify

[10.011589] cgroup_file_notify

[10.011593] try_charge_memcg (4) memcg accounting raises an

[10.011597] obj_cgroup_charge_pages MEMCG_MAX event

[10.011599] obj_cgroup_charge_account

[10.011600] __memcg_slab_post_alloc_hook

[10.011603] __kmalloc_node_noprof

...

[10.011611] bpf_map_kmalloc_node

[10.011612] __bpf_async_init

[10.011615] bpf_timer_init (3) BPF calls bpf_timer_init()

[10.011617] bpf_prog_xxxxxxxxxxxxxxxx_fcg_runnable

[10.011619] bpf__sched_ext_ops_runnable

[10.011620] enqueue_task_scx (2) BPF runs with rq_lock held

[10.011622] enqueue_task

[10.011626] ttwu_do_activate

[10.011629] sched_ttwu_pending (1) grabs rq_lock

...

The above was reproduced on bpf-next (b338cf849ec8) by modifying

./tools/sched_ext/scx_flatcg.bpf.c to call bpf_timer_init() during

ops.runnable(), and hacking the memcg accounting code a bit to make

a bpf_timer_init() call more likely to raise an MEMCG_MAX event.

We have also run into other similar variants (both internally and on

bpf-next), including double-acquiring cgroup_file_kn_lock, the same

worker_pool::lock, etc.

As suggested by Shakeel, fix this by using __GFP_HIGH instead of

GFP_ATOMIC in __bpf_async_init(), so that e.g. if try_charge_memcg()

raises an MEMCG_MAX event, we call __memcg_memory_event() with

@allow_spinning=false and avoid calling cgroup_file_notify() there.

Depends on mm patch

"memcg: skip cgroup_file_notify if spinning is not allowed":

https://lore.kernel.org/bpf/[email protected]/

v0 approach s/bpf_map_kmalloc_node/bpf_mem_alloc/

https://lore.kernel.org/bpf/[email protected]/

v1 approach:

https://lore.kernel.org/bpf/[email protected]/