Bug 2540245 (CVE-2026-93240)

Summary: CVE-2026-93240 kernel: memcg: make the v1 soft limit knob inert
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: low Docs Contact:
Priority: low    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, 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's memory control group (memcg) subsystem. A local user with permissions to configure memory limits can cause a Denial of Service (DoS) by triggering memory reclamation under legacy memory soft limits. When the kernel's background memory reclamation process manages memory under these settings, it invokes an improper function path that results in a kernel warning and potential system instability.
 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 2026-09-24 15:52:54 UTC 
In the Linux kernel, the following vulnerability has been resolved:

memcg: make the v1 soft limit knob inert

The v1 soft limit has been deprecated since v6.12 and nobody has reported
depending on it.  Start the removal by decoupling the interface from the
implementation: keep memory.soft_limit_in_bytes, but ignore writes to it
and always report the maximum value on read similar to what
memory.kmem.limit_in_bytes already does.

Writes are still parsed, so malformed input keeps returning -EINVAL.  The
knob now also behaves the same everywhere: it used to return -EOPNOTSUPP
on PREEMPT_RT, where soft limit reclaim has always been disabled.

This also fixes the syzbot report linked below.  Soft limit reclaim is the
only caller that runs shrink_lruvec() from kswapd against a specific
memcg, so it is the only way to reach lru_gen_shrink_lruvec() and in turn
set_mm_walk(), which warns when called from kswapd.
Comment 1 gkamathe 2026-09-28 07:47:54 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-93240.mbox