Bug 2468085 (CVE-2026-43292)

Summary: CVE-2026-43292 kernel: mm/vmalloc: prevent RCU stalls in kasan_release_vmalloc_node
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: ---
Doc Text:
A flaw was found in the Linux kernel. When the CONFIG_PAGE_OWNER option is enabled, the kernel's memory management (mm/vmalloc) component can experience Read-Copy-Update (RCU) stalls during virtual memory allocation cleanup. This occurs because freeing Kernel Address Sanitizer (KASAN) shadow pages triggers expensive stack unwinding operations that acquire RCU read locks. Processing a large number of pages without yielding the CPU can cause tasks to hold the CPU for extended periods, leading to RCU stalls and potential Out-Of-Memory (OOM) conditions, effectively resulting in a Denial of Service.
 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 2026-05-08 14:03:44 UTC 
In the Linux kernel, the following vulnerability has been resolved:

mm/vmalloc: prevent RCU stalls in kasan_release_vmalloc_node

When CONFIG_PAGE_OWNER is enabled, freeing KASAN shadow pages during
vmalloc cleanup triggers expensive stack unwinding that acquires RCU read
locks.  Processing a large purge_list without rescheduling can cause the
task to hold CPU for extended periods (10+ seconds), leading to RCU stalls
and potential OOM conditions.

The issue manifests in purge_vmap_node() -> kasan_release_vmalloc_node()
where iterating through hundreds or thousands of vmap_area entries and
freeing their associated shadow pages causes:

  rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
  rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P6229/1:b..l
  ...
  task:kworker/0:17 state:R running task stack:28840 pid:6229
  ...
  kasan_release_vmalloc_node+0x1ba/0xad0 mm/vmalloc.c:2299
  purge_vmap_node+0x1ba/0xad0 mm/vmalloc.c:2299

Each call to kasan_release_vmalloc() can free many pages, and with
page_owner tracking, each free triggers save_stack() which performs stack
unwinding under RCU read lock.  Without yielding, this creates an
unbounded RCU critical section.

Add periodic cond_resched() calls within the loop to allow:
- RCU grace periods to complete
- Other tasks to run
- Scheduler to preempt when needed

The fix uses need_resched() for immediate response under load, with a
batch count of 32 as a guaranteed upper bound to prevent worst-case stalls
even under light load.
Comment 1 Keith Grant 2026-05-08 18:15:09 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026050853-CVE-2026-43292-a97d@gregkh/T