From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-93240][LOW] memcg: make the v1 soft limit knob inert Date: Thu, 24 Sep 2026 13:46:30 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-93240 X-AL-KERNEL-Priority: LOW X-AL-KERNEL-Severity: LOW X-AL-KERNEL-Base-Severity: LOW X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 0 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 72fb67f6e0e5d78e4f34cf9929d1afdb0fd54203 List-Id: CVE: CVE-2026-93240 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: memcg: make the v1 soft limit knob inert Commit: 72fb67f6e0e5d78e4f34cf9929d1afdb0fd54203 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=72fb67f6e0e5d78e4f34cf9929d1afdb0fd54203 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93240 Analysis date: Thu, 24 Sep 2026 13:46:30 -0400 ActionableScore: 0 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-93240 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93240 The original announcement does not normally provide a security severity estimate, CVSS assessment, or enough information to determine whether the reported kernel bug represents a practically relevant security issue. This report was generated by AL-KERNEL, an AI-assisted Linux kernel vulnerability analysis system developed by Alexander Larkin. It combines an autonomous classifier with LLM-assisted technical analysis and a separate ActionableScore mechanism. The purpose of this report is to prioritize Linux kernel CVEs before manual review, identify cases that require prompt investigation, and support automatic closure of issues that are unlikely to have meaningful security impact. Published priority for this report: LOW Manual review required: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-93240 LOW https://www.kernelcve.org/list/?q=CVE-2026-93240 CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:N';CWE-670;CWE-754;BEST CVSS score: '0';DESCR 'The deprecated cgroup v1 memory.soft_limit_in_bytes interface can enable soft limit reclaim, which is the only path that invokes shrink_lruvec for a specific memcg from kswapd and reaches a warning in set_mm_walk. The reported behavior is a kernel warning caused by an unsupported execution context. The patch context does not demonstrate a crash, memory corruption, information disclosure, privilege escalation, or realistic resource exhaustion primitive. For the CVSS the PR:L reflects that a local process needs access to the cgroup interface, but C:N I:N A:N applies because no security impact is demonstrated. The issue is not network reachable.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) YES LEAK LINUS SYZBOT MEMORY DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=0 PrimitiveClass=NONE RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 0 * Conservative score: 0 * Raw paranoid score: 0 * Paranoid score: 0 * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +0: The patch establishes a deprecated cgroup v1 soft-limit reclaim path that can reach a WARN in set_mm_walk when invoked from kswapd. * +0: WARN-only behavior is not evidence of a kernel crash, memory corruption, information disclosure, integrity violation, privilege escalation, or persistent resource exhaustion. * +0: No UAF, refcount misuse, double release, stale object, out-of-bounds access, ownership violation, or authorization bypass is shown. * +0: No remote reachability is established. The interface is a local cgroup v1 control file. * +0: No reliable availability impact is established. The supplied evidence identifies a warning, not a panic, Oops, deadlock, or host-wide stall. * No negative privilege penalty was applied. Access control for a particular cgroup hierarchy may be delegated, but the complete applicable privilege boundary is not shown and is irrelevant because no security primitive is established. * No configuration or legacy-mode penalty was applied. Although cgroup v1 soft limits are deprecated, this does not reduce an already zero security-impact score. 3. Reachability analysis The affected interface is the local cgroup v1 memory.soft_limit_in_bytes file. A process must be able to write to the relevant cgroup control file, but the supplied patch does not establish whether this requires host-admin-equivalent authority, delegated cgroup management rights, or ownership of an attacker-controlled cgroup. Namespace-scoped reachability is unresolved. Cgroup delegation can exist, but the input does not establish that an ordinary unprivileged user can create the relevant cgroup, write the knob, induce the reclaim path, and obtain a security-relevant result. No network path, special hardware prerequisite, boot option, sysctl prerequisite, race condition, attacker-controlled payload, or persistent resource-consumption mechanism is established. 4. Primitive and severity interpretation The patch removes the operational effect of the deprecated cgroup v1 soft-limit interface. Previously, a valid write could set memcg soft-limit state and enable soft-limit reclaim behavior. That reclaim path could call shrink_lruvec from kswapd for a specific memcg and eventually reach set_mm_walk, which emits a warning for that execution context. The demonstrated issue is an invalid-state or unsupported-context warning. It is not an active-object lifetime violation, UAF, stale-reference use, double release, refcount mutation, controlled overwrite, semantic security-boundary bypass, or ownership/COW violation. PrimitiveClass is NONE because no meaningful corruption, lifetime, authorization, disclosure, or integrity primitive is established. RealUAF is NO. There is no demonstrated consequence beyond a warning, and no technically grounded paranoid escalation is available. ImportantCandidate is NO and AutoDowngradeAllowed is YES because automatic closure would not discard an unresolved security primitive. Likely operational severity is non-security maintenance or diagnostics. It may be relevant for warning reduction and removal of deprecated functionality, but it is not actionable as a kernel security vulnerability from the supplied evidence. 5. One-sentence report phrase The deprecated cgroup v1 memory.soft_limit_in_bytes interface could reach a WARN path when soft-limit reclaim invokes memory walking from kswapd, but the supplied patch establishes no crash, memory corruption, disclosure, privilege escalation, or security-boundary impact. 6. Manual review recommendation NO MANUAL CHECK NEEDED The patch and supplied context establish a WARN-only deprecated-feature cleanup without a concrete security primitive or plausible unsupported high-impact consequence. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: memcg: make the v1 soft limit knob inert Commit: 72fb67f6e0e5d78e4f34cf9929d1afdb0fd54203 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=72fb67f6e0e5d78e4f34cf9929d1afdb0fd54203 Commit description: 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. Link: https://lore.kernel.org/20260811203203.3456029-2-shakeel.butt@linux.dev Signed-off-by: Shakeel Butt Reported-by: syzbot+12ee2725d5fde63a9c96@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/6a7a6929.b50370da.49fe0.005e.GAE@google.com/ Acked-by: Michal Hocko Cc: Axel Rasmussen Cc: Barry Song Cc: David Hildenbrand Cc: Johannes Weiner Cc: Kairui Song Cc: Lorenzo Stoakes Cc: Muchun Song Cc: Roman Gushchin Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman Changed files: mm/memcontrol-v1.c Diff excerpt: Not included in this email. See the upstream URL for the full patch. Full patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=72fb67f6e0e5d78e4f34cf9929d1afdb0fd54203 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-93240 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93240 The original CVE announcement normally does not include a security-level estimate. In particular, it may not contain a CVSS assessment, an impact level, or enough information to determine whether the reported bug is a practically relevant security issue. One purpose of this parallel CVE list is to provide that missing technical and prioritization information. The original goal of the AL-KERNEL project was to prioritize Linux kernel CVE analysis automatically before manual review. The system can also help identify non-security issues that may be suitable for automatic closure. This report was generated by AL-KERNEL, an AI-assisted Linux kernel vulnerability analysis system developed by Alexander Larkin. The first analysis stage combines an autonomous classifier with additional LLM-based analysis. The autonomous classifier runs locally on a CPU and is based on a backpropagation neural network. Together, these mechanisms produce a technical vulnerability description, identify likely weakness types, estimate CVSS severity, and provide input for ActionableScore. Two CVSS estimates are retained because incomplete kernel vulnerability information often permits more than one defensible interpretation: Conservative CVSS vector: Not available The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:N The Best / paranoid CVSS score: 0 The conservative vector represents a lower-impact interpretation. The Best/paranoid vector intentionally represents a plausible upper-bound interpretation and should not automatically be treated as demonstrated real-world impact. CVSS may also need to be adjusted for a particular Linux deployment, because actual reachability, privileges, enabled kernel configuration, hardware, namespaces, exposed device nodes, and other environmental conditions can differ significantly between systems. A separate ActionableScore mechanism evaluates practical remediation urgency. Its analysis may include reachability, attack prerequisites, subsystem exposure, memory-corruption characteristics, denial-of-service reliability, and possible confidentiality, integrity, or privilege-escalation impact. Conservative ActionableScore: unknown Paranoid ActionableScore: 0 The final base severity is taken directly from the second tab-separated field of the AL-KERNEL classification result. ActionableScore does not replace or independently override that final AL-KERNEL decision, and if ActionableScore adjusted impact level of ALKERNEL, then you would see self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7. For an AL-KERNEL result of MODERATE, this report uses the following additional presentation split: ActionableScore below 5 -> MODERATE REGULAR ActionableScore 5 or more -> MODERATE 7.0 The distinction between MODERATE REGULAR and MODERATE 7.0 makes it possible to identify Moderate issues that should receive manual analysis and fixes before lower-priority MODERATE REGULAR issues. In many cases, MODERATE REGULAR fixes may wait for a later rebase or routine update. There is one override in which MODERATE REGULAR becomes MODERATE 7.0 even when the ActionableScore is below 5. When the AL-KERNEL result contains the KPANIC flag, a MODERATE result is always presented as MODERATE 7.0. The KPANIC flag selected with few regexps without usage of AI at all, so it helps to detect cases when Kernel Crash happens and similar (to filter False-Negative results from the LLM usage). KPANIC indicates that a reliable kernel crash, kernel panic, or similarly serious kernel availability impact was identified by the classification workflow. AL-KERNEL base severity for this report: LOW KPANIC detected for this report: NO Published priority for this report (same as in Subject): LOW These results are intended to support engineering triage. They are machine-generated estimates, and cases marked for manual review should be validated by a human security engineer before final disposition. For more info read docs linked from here: https://kernelcve.org/ (and you can submit you own patch there to generate such a report for non-existant CVE-id yet). Note that in many cases this AI tool selects higher severity, than real is (means you can expect Importants instead of Moderate 7.0 or Moderates 7.0 instead of regular Moderates). If you see such cases, please use reply email interface to add additional manual analyses info to this particular CVE. And please, please, let me know when you see Lows instead of Importants or Important instead of Low (because particular for such cases I need to tune this AI tool to make it better for this one and next similar). My contact email for such notifications is alexanjelausa@gmail.com (and both send reply to CVE record itself too and see "reply" button below for howto reply).