From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98376][MODERATE 7.0] bpf: Use array_map_meta_equal for percpu array inner map replacement percpu_array_map_ops.map_meta_equal points to the generic bpf_map_meta_equal(), which does not compare max_entries. When a percpu array serves as an inner map, replacing it with one that has fewer max_entries bypasses the check. Since percpu_array_map_gen_lookup() inlines the original template's index_mask as a JIT immediate, a lookup on the replacement map can access pptrs[] out of bounds. Point percpu_array_map_ops.map_meta_equal to array_map_meta_equal(), which already enforces the max_entries equality check. Add a selftest to verify that replacing a percpu array inner map with a differently-sized one is rejected. Fixes: db69718 ("bpf: inline bpf_map_lookup_elem() for PERCPU_ARRAY maps") Signed-off-by: Guannan Wang Acked-by: Mykyta Yatsenko Link: https://lore.kernel.org/r/20260514074454.77491-1-wgnbuaa@gmail.com Signed-off-by: Alexei Starovoitov Date: Fri, 09 Oct 2026 22:25:04 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98376 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: 4 X-AL-KERNEL-Commit: 593980175389a05793f6060aa20e626330960395 List-Id: CVE: CVE-2026-98376 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: bpf: Use array_map_meta_equal for percpu array inner map replacement percpu_array_map_ops.map_meta_equal points to the generic bpf_map_meta_equal(), which does not compare max_entries. When a percpu array serves as an inner map, replacing it with one that has fewer max_entries bypasses the check. Since percpu_array_map_gen_lookup() inlines the original template's index_mask as a JIT immediate, a lookup on the replacement map can access pptrs[] out of bounds. Point percpu_array_map_ops.map_meta_equal to array_map_meta_equal(), which already enforces the max_entries equality check. Add a selftest to verify that replacing a percpu array inner map with a differently-sized one is rejected. Fixes: db69718 ("bpf: inline bpf_map_lookup_elem() for PERCPU_ARRAY maps") Signed-off-by: Guannan Wang Acked-by: Mykyta Yatsenko Link: https://lore.kernel.org/r/20260514074454.77491-1-wgnbuaa@gmail.com Signed-off-by: Alexei Starovoitov Commit: 593980175389a05793f6060aa20e626330960395 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=593980175389a05793f6060aa20e626330960395 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98376 Analysis date: Fri, 09 Oct 2026 22:25:04 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98376 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98376 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: MODERATE 7.0 Manual review required: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-98376 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98376 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE_KPANIC RESULT=SAME (legacy and Aegis reconciliation agree; DECISION: both MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-129;CWE-125;*CWE-787;*CWE-20;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'A BPF map compatibility check can allow a PERCPU_ARRAY inner map to be replaced with a smaller map because max_entries is not compared. The JIT compiled lookup continues to use the index_mask from the original template and can therefore access the replacement map pptrs array out of bounds. The immediate primitive is an out of bounds pointer load. Subsequent BPF access through the resulting per CPU value pointer creates a plausible path to an invalid kernel memory read or write, a kernel crash, information exposure, or local privilege escalation. For the CVSS the PR:L in the paranoid score reflects systems where unprivileged BPF is enabled or limited BPF capabilities are delegated to a local user or service account. The typical hardened configuration requires stronger BPF capabilities and is represented by PR:H in the base score. The issue is not network reachable and requires local BPF operations. Impact may include confidentiality, integrity, and availability compromise and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE OOB INIT BPF HARDWARE TEST KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=4 PrimitiveClass=CLASS_B RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO RequiresHostUID0=UNKNOWN AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw conservative score: 4. * Conservative score: 4. No floor or cap changed the score. * Raw paranoid score: 5. * Paranoid score: 5. The BPF privileged-control-plane cap does not change it. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown Conservative signals: * +1 Weak or indirect corruption candidate. The smaller replacement map is accepted while JIT code retains the original larger `index_mask`, causing an out-of-bounds load from `pptrs[]`. * +1 Weak exploitation concern. The value loaded outside `pptrs[]` is treated as the per-CPU map-value pointer, so later JIT-generated BPF operations can consume an invalid kernel pointer rather than merely detect the bad index. * +1 Reliable kernel crash or strong DoS. Dereferencing an invalid per-CPU value pointer can realistically fault the kernel. No additional Availability point is awarded for the same failure. * +1 Memory-layout invariant restoration. The patch restores consistency between the replacement map allocation size and the bounds embedded into previously generated JIT code. This is relevant beyond generic validation because the stale immediate remains operational after map replacement. Paranoid difference: * The weak exploitation concern is interpreted as +2 strong unresolved exploitation leverage instead of +1. A BPF lookup returns a verifier-trusted map-value pointer, and normal BPF value operations may read or write through that pointer. This supports mandatory review, but it does not establish an arbitrary target, controlled payload destination, or completed LPE. Not awarded: * No UAF, controlled reclaim, callback hijack, refcount takeover, or repeated lifetime mutation is established. * No arbitrary or directed kernel write is demonstrated. * No confidentiality or integrity bonus is awarded because no concrete disclosure, protected victim, or controlled corruption target is identified. * No local-unprivileged bonus is awarded because the complete BPF load, JIT, map replacement, and execution privilege boundary is unresolved. * No remote-reachability bonus applies. * No race or timing penalty applies because this is a deterministic metadata-compatibility failure. * B5-R is not established. There is no retry-accumulated index and the patch directly establishes an out-of-bounds `pptrs[]` access, not the required retry-accumulated heap OOB write. * B3-PENDING is not established because no shared or file-backed storage write is involved. * B4-PENDING is not established because this is not an authorization decision bypass. 3. Reachability analysis The attacker must create a `PERCPU_ARRAY` template, create an `ARRAY_OF_MAPS`, replace its inner map with a smaller compatible-looking `PERCPU_ARRAY`, load or execute JIT-generated BPF code using the original template bounds, and select an index valid under the old mask but outside the replacement map. The supplied evidence does not establish whether that complete sequence is available to an ordinary user in the evaluated product. Hardened systems commonly disable unprivileged BPF and gate relevant operations through `CAP_BPF`, `CAP_SYS_ADMIN`, or related controls, but the exact checks and capability scope are not supplied. Therefore `HostAdminRequired` and `NamespaceScopedPrivilege` remain `UNKNOWN`, and no privilege penalty or unprivileged bonus is applied. No attachment to a network device is inherently required by the shown map primitive. Network namespaces alone would not prove complete namespace-scoped reachability. JIT availability and root-controlled unprivileged-BPF policy are relevant prerequisites. No special hardware, remote traffic, retry loop, or race is required. 4. Primitive and severity interpretation The exact immediate primitive is an out-of-bounds pointer load from the replacement map's `pptrs[]` array caused by JIT code retaining the template map's larger `index_mask`. The resulting value is then interpreted as a per-CPU map-value pointer and can be consumed by later BPF value accesses. This is not a UAF and does not involve stale storage after object destruction. It is active structured-state corruption caused by disagreement between JIT-embedded bounds and the live inner map allocation. `CLASS_B` is appropriate because a real kernel OOB pointer primitive and subsequent corrupted-pointer consumption are established, while controlled destination selection, arbitrary kernel read or write, protected-object corruption, and privilege escalation are not. The demonstrated practical consequence is at least a credible kernel crash. The paranoid interpretation preserves the possibility of more useful kernel memory access because BPF can perform normal value operations through the invalid pointer. `ImportantCandidate=YES` and `AutoDowngradeAllowed=NO` are justified by the active OOB-derived pointer being accepted as a map-value pointer, leaving meaningful exploitation leverage unresolved. This is not enough for `CLASS_A` without evidence of controlled target selection, reliable disclosure, directed write, or LPE. 5. One-sentence report phrase A smaller PERCPU_ARRAY inner map can retain the original JIT index mask and cause an out-of-bounds pptrs pointer load whose result is consumed as a BPF map-value pointer, creating a kernel crash risk and an unresolved kernel memory-access primitive. 6. Manual review recommendation MANUAL CHECK REQUIRED The OOB-loaded pointer crosses into later JIT-generated map-value processing, so determining allocator adjacency, pointer usability, available BPF load privileges, and whether controlled read or write can be constructed requires manual analysis. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: bpf: Use array_map_meta_equal for percpu array inner map replacement percpu_array_map_ops.map_meta_equal points to the generic bpf_map_meta_equal(), which does not compare max_entries. When a percpu array serves as an inner map, replacing it with one that has fewer max_entries bypasses the check. Since percpu_array_map_gen_lookup() inlines the original template's index_mask as a JIT immediate, a lookup on the replacement map can access pptrs[] out of bounds. Point percpu_array_map_ops.map_meta_equal to array_map_meta_equal(), which already enforces the max_entries equality check. Add a selftest to verify that replacing a percpu array inner map with a differently-sized one is rejected. Fixes: db69718 ("bpf: inline bpf_map_lookup_elem() for PERCPU_ARRAY maps") Signed-off-by: Guannan Wang Acked-by: Mykyta Yatsenko Link: https://lore.kernel.org/r/20260514074454.77491-1-wgnbuaa@gmail.com Signed-off-by: Alexei Starovoitov Commit: 593980175389a05793f6060aa20e626330960395 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=593980175389a05793f6060aa20e626330960395 Changed files: kernel/bpf/arraymap.c tools/testing/selftests/bpf/prog_tests/percpu_array_inner_map.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=593980175389a05793f6060aa20e626330960395 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98376 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98376 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:L/PR:H/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 7.8 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: 4 Paranoid ActionableScore: 5 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: MODERATE KPANIC detected for this report: YES Published priority for this report (same as in Subject): MODERATE 7.0 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).