Bug 2396941 (CVE-2025-39843)

Summary:	CVE-2025-39843 kernel: mm: slub: avoid wake up kswapd in set_track_prepare
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	Keywords:	Security
Target Milestone:	---
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A deadlock lock recursion vulnerability exists in the linux kernel such that when CONFIG_DEBUG_OBJECTS_TIMERS is set, may wake up kswapd in set_track_prepare, and try to hold the per_cpu(hrtimer_bases) lock.	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2025-09-19 16:03:08 UTC

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

mm: slub: avoid wake up kswapd in set_track_prepare

set_track_prepare() can incur lock recursion.
The issue is that it is called from hrtimer_start_range_ns
holding the per_cpu(hrtimer_bases)[n].lock, but when enabled
CONFIG_DEBUG_OBJECTS_TIMERS, may wake up kswapd in set_track_prepare,
and try to hold the per_cpu(hrtimer_bases)[n].lock.

Avoid deadlock caused by implicitly waking up kswapd by passing in
allocation flags, which do not contain __GFP_KSWAPD_RECLAIM in the
debug_objects_fill_pool() case. Inside stack depot they are processed by
gfp_nested_mask().
Since ___slab_alloc() has preemption disabled, we mask out
__GFP_DIRECT_RECLAIM from the flags there.

The oops looks something like:

BUG: spinlock recursion on CPU#3, swapper/3/0
 lock: 0xffffff8a4bf29c80, .magic: dead4ead, .owner: swapper/3/0, .owner_cpu: 3
Hardware name: Qualcomm Technologies, Inc. Popsicle based on SM8850 (DT)
Call trace:
spin_bug+0x0
_raw_spin_lock_irqsave+0x80
hrtimer_try_to_cancel+0x94
task_contending+0x10c
enqueue_dl_entity+0x2a4
dl_server_start+0x74
enqueue_task_fair+0x568
enqueue_task+0xac
do_activate_task+0x14c
ttwu_do_activate+0xcc
try_to_wake_up+0x6c8
default_wake_function+0x20
autoremove_wake_function+0x1c
__wake_up+0xac
wakeup_kswapd+0x19c
wake_all_kswapds+0x78
__alloc_pages_slowpath+0x1ac
__alloc_pages_noprof+0x298
stack_depot_save_flags+0x6b0
stack_depot_save+0x14
set_track_prepare+0x5c
___slab_alloc+0xccc
__kmalloc_cache_noprof+0x470
__set_page_owner+0x2bc
post_alloc_hook[jt]+0x1b8
prep_new_page+0x28
get_page_from_freelist+0x1edc
__alloc_pages_noprof+0x13c
alloc_slab_page+0x244
allocate_slab+0x7c
___slab_alloc+0x8e8
kmem_cache_alloc_noprof+0x450
debug_objects_fill_pool+0x22c
debug_object_activate+0x40
enqueue_hrtimer[jt]+0xdc
hrtimer_start_range_ns+0x5f8
...

Comment 1 Jon Moroney 2025-09-19 16:31:08 UTC

Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025091903-CVE-2025-39843-0702@gregkh/T