From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-99244][LOW] pid_namespace: prevent TIF_NOTIFY_SIGNAL from interrupting the reaper Date: Tue, 03 Nov 2026 22:59:09 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-99244 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: 1 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 2c20ace1698d03a23467351be1d281e89b36ade3 List-Id: CVE: CVE-2026-99244 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: pid_namespace: prevent TIF_NOTIFY_SIGNAL from interrupting the reaper Commit: 2c20ace1698d03a23467351be1d281e89b36ade3 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2c20ace1698d03a23467351be1d281e89b36ade3 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99244 Analysis date: Tue, 03 Nov 2026 22:59:09 -0400 ActionableScore: 1 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: Concurrent notification signaling can keep a PID-namespace reaper busy-looping, consuming CPU and delaying namespace teardown without a shown corruption or authorization primitive. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99244 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99244 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-2026-99244 LOW https://www.kernelcve.org/list/?q=CVE-2026-99244 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT LOW AEGIS_AS=0 LEGACY=LOW RESULT=SAME (final reconciliation agrees; DECISION: both LOW) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-835;**CWE-400;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'The PID namespace reaper can enter a CPU busy loop because TIF_NOTIFY_SIGNAL may be raised again after it is cleared and signal_pending then prevents kernel_wait4 or an interruptible schedule from sleeping. A demonstrated trigger is concurrent live patch signaling through klp_send_signals while the namespace reaper is waiting for process cleanup. For the CVSS the PR:L value reflects that a local user or container workload may control PID namespace lifetime when namespace creation is delegated, while reliable reproduction also depends on a concurrent kernel notification source such as a privileged live patch operation. The demonstrated impact is delayed namespace teardown and CPU consumption. There is no evidence of UAF, OOB access, information disclosure, or a write primitive. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 4.7 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 0 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was LOW. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) MAYBE SIMPLEFIX LEAK LINUS - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=1 PrimitiveClass=NONE RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES RequiresHostUID0=UNKNOWN AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 1 * Conservative score: 1 * Raw paranoid score: 1 * Paranoid score: 1 * No floor or cap applied. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +1 availability/resource-consumption effect: repeatedly raised `TIF_NOTIFY_SIGNAL` prevents `kernel_wait4()` and interruptible scheduling from sleeping, causing reaper busy-wait and delayed PID-namespace teardown. * No crash point: the patch supports CPU consumption and teardown delay, not a kernel panic or host-wide fatal fault. * No corruption point: no UAF, OOB access, invalid lifetime operation, or write primitive is present. * No authorization point: `no_notify_signal` changes signal-pending/scheduling behavior, not a DENY-to-ALLOW security decision. * B5-R does not apply: there is no heap OOB write, retry-accumulated offset, or later consumption of corrupted structured state. * B3-PENDING does not apply: no shared-backing write exists. * No extra availability point: persistent host-wide exhaustion or lasting unavailability is not shown. 3. Reachability analysis The demonstrated sequence is compound: a PID-namespace reaper must be in teardown while another source, exemplified by privileged livepatch signaling through `klp_send_signals()`, repeatedly sets `TIF_NOTIFY_SIGNAL`. A delegated container workload may influence namespace lifetime, but the evidence does not show that the same below-host-admin actor controls the notification source or complete trigger. Therefore host-admin and namespace-scoped reachability remain unknown. No special hardware is required; timing coordination is relevant, but no separate race penalty is applied. 4. Primitive and severity reading The exact defect is a scheduling-state busy loop: clearing `TIF_NOTIFY_SIGNAL` once is ineffective because it may be raised again. The guard makes `signal_pending()` ignore that flag while the namespace reaper waits. This is `PrimitiveClass=NONE`: the shown consequence is bounded to CPU consumption and delayed cleanup, with no memory corruption, protected-state modification, auth bypass, or demonstrated host-wide crash. Important-candidate preservation rules do not apply, and automatic downgrade is allowed. 5. One-sentence report phrase Concurrent notification signaling can keep a PID-namespace reaper busy-looping, consuming CPU and delaying namespace teardown without a shown corruption or authorization primitive. 6. Manual review advice NO MANUAL CHECK NEEDED The patch and supplied evidence support an ordinary availability bug without an unresolved Important-class primitive. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: pid_namespace: prevent TIF_NOTIFY_SIGNAL from interrupting the reaper Commit: 2c20ace1698d03a23467351be1d281e89b36ade3 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2c20ace1698d03a23467351be1d281e89b36ade3 Commit description: Since commit 7fea700 ("zap_pid_ns_processes: clear TIF_NOTIFY_SIGNAL along with TIF_SIGPENDING") zap_pid_ns_processes() clears TIF_NOTIFY_SIGNAL before every kernel_wait4() call. Otherwise kernel_wait4() doesn't sleep and returns -ERESTARTSYS if signal_pending() is true and the reaper busy-waits. But clearing TIF_NOTIFY_SIGNAL doesn't fix it. It can get raised again. For example, klp_send_signals() sets it raw against any task that hasn't transitioned yet. And it keeps sending it until the livepatch finishes. The sleep loop waiting for pid_allocated to drop has the same problem and it doesn't even clear anything. So a schedule() in TASK_INTERRUPTIBLE returns immediately. Use a no_notify_signal guard. signal_pending() will ignore TIF_NOTIFY_SIGNAL and the pid namespace reaper sleeps until a child exits or free_pid() wakes it. Link: https://patch.msgid.link/20260824-work-tif_notify_signal-v2-5-6609e42b3157@kernel.org Fixes: 7fea700 ("zap_pid_ns_processes: clear TIF_NOTIFY_SIGNAL along with TIF_SIGPENDING") Reviewed-by: Oleg Nesterov Cc: stable@vger.kernel.org Suggested-by: Oleg Nesterov Signed-off-by: Christian Brauner (Amutable) Signed-off-by: Greg Kroah-Hartman Changed files: kernel/pid_namespace.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=2c20ace1698d03a23467351be1d281e89b36ade3 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99244 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99244 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: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 4.7 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: 1 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).