From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-89580][MODERATE 7.0] bpf: Disable preemption in __bpf_get_stack Date: Fri, 11 Sep 2026 17:37:18 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-89580 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: unknown X-AL-KERNEL-Commit: 8c5ba022f2085ea42d011497a6e92e527d123b9b List-Id: CVE: CVE-2026-89580 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: bpf: Disable preemption in __bpf_get_stack Commit: 8c5ba022f2085ea42d011497a6e92e527d123b9b Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8c5ba022f2085ea42d011497a6e92e527d123b9b Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89580 Analysis date: Fri, 11 Sep 2026 17:37:18 -0400 ActionableScore: 5 ActionableScore lower bound: unknown 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-2026-89580 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89580 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-2026-89580 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89580 CHECK WITH IMPACT FROM ORIG NN IMPORTANT Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in __bpf_get_stack can occur because get_perf_callchain returns a per CPU perf_callchain_entry and releases its recursion slot before the helper finishes copying the entry into the caller buffer. On a PREEMPT kernel, a preemptible BPF program can be scheduled out after obtaining the callchain entry, and another task on the same CPU can reuse the same per CPU buffer and overwrite trace nr with a larger value. The inflated trace nr can make copy_len exceed the verified caller buffer and cause an out of bounds write in memcpy or in the build_id path. For the CVSS the PR:L is used for the paranoid score because BPF access can be delegated to a less than fully privileged local user or service account in some deployments. The issue is not network reachable and requires local ability to load or run an affected BPF program. Impact is at least local denial of service via kernel memory corruption and in worst case may allow confidentiality, integrity, and availability impact due to an out of bounds write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) YES WRITE OOB BPF UAF HARDWARE KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN6 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 PrimitiveClass=CLASS_A RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO 1. ActionableScore * Raw conservative score: 4 * Conservative score: 5 * Raw paranoid score: 5 * Paranoid score: 5 * Applied conservative floor/cap: 4 -> 5 because a concrete kernel out-of-bounds write primitive is established and should not be auto-downgraded below actionable review. * Applied paranoid floor/cap: none. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown Positive signals: * +2 Strong kernel corruption primitive. The patch text directly states that inflated trace->nr can make copy_len exceed the caller buffer, causing an out-of-bounds write in memcpy and in the build_id path. * +1 Reliable kernel crash / strong DoS. A kernel OOB write in a BPF helper can realistically crash or corrupt kernel memory. * +1 Attacker-influenced active state / repeatable lifetime-like manipulation. The vulnerable state is a per-CPU perf_callchain_entry reused by another task on the same CPU while __bpf_get_stack consumes it, and trace->nr is the exploitation-relevant value. * +1 paranoid Weak LPE concern. The primitive is not merely a NULL dereference or warning. It is an OOB write with attacker-influenced length in kernel context, but target and payload control are not shown enough for stronger leverage. Negative or non-awarded signals: * No -1 race penalty. The bug is a race, but the supplied evidence does not establish a narrow one-shot or externally uncontrollable race. * No -2 host-admin penalty. Host-admin-equivalent privilege is not positively established from the supplied evidence. * No Local unprivileged trigger bonus. BPF program loading and attachment privileges are unresolved and commonly gated. * No remote reachability bonus. This is a local BPF/perf helper path, not a packet-triggered or network service path. * No UAF score. This is a per-CPU buffer reuse race causing OOB write, not a demonstrated use-after-free. * No arbitrary write bonus. The patch establishes an OOB write, but not arbitrary target selection or fully attacker-controlled payload. * No controlled reclaim or callback hijack demonstrated. * No extra Availability point. The crash/corruption consequence is already counted once. * No C/I points are awarded solely from theoretical exploitability, but C/I remain unresolved due to the concrete OOB write. 3. Reachability analysis The trigger requires local ability to load or run an affected BPF program using bpf_get_stack in a preemptible context, such as a non-sleepable raw tracepoint program on a PREEMPT kernel. BPF access may require CAP_BPF, CAP_PERFMON, CAP_SYS_ADMIN, or product-specific delegation, so HostAdminRequired is UNKNOWN rather than YES or NO. NamespaceScopedPrivilege is UNKNOWN. The supplied patch does not establish that the complete load, attach, execution, and trigger chain is available inside attacker-created namespaces. Prior host setup may matter because unprivileged BPF is commonly disabled and BPF policy is controlled by sysctls and capabilities. PREEMPT kernel configuration is relevant. No special hardware is required. The issue is not network reachable. 4. Primitive and severity interpretation The exact primitive is an out-of-bounds kernel write caused by a race on a per-CPU perf callchain buffer. get_perf_callchain returns a buffer and releases the recursion slot before __bpf_get_stack finishes copying from it. If the BPF program is preempted, another task on the same CPU can reuse the buffer and increase trace->nr, causing copy_len to exceed the verified caller buffer. This is active shared per-CPU storage reuse, not fixed stale storage and not a UAF. The demonstrated consequence is kernel memory corruption and likely DoS. The speculative consequence is privilege escalation if the OOB write can be shaped into useful corruption, but controlled target, controlled payload, arbitrary R/W, or a complete LPE chain is not established. PrimitiveClass is CLASS_A because a concrete attacker-influenced OOB write in kernel context is directly established. ImportantCandidate is YES because this is a real kernel corruption primitive requiring exploitation-leverage review. AutoDowngradeAllowed is NO because automatic Moderate closure would discard a concrete OOB write primitive with unresolved exploitation impact. Likely operational severity is Actionable Moderate at minimum, with Strong Important review warranted depending on product BPF exposure and whether the OOB write can be made exploitable beyond crash. 5. One-sentence report phrase A race in __bpf_get_stack can let a preemptible BPF program consume a reused per CPU perf callchain buffer with an inflated trace nr value, causing an out of bounds kernel write and requiring manual review for possible impact beyond local DoS. 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the patch establishes a concrete kernel out-of-bounds write primitive in a BPF helper, and the practical severity depends on BPF reachability and whether the overflow can be shaped into useful kernel corruption. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: bpf: Disable preemption in __bpf_get_stack Commit: 8c5ba022f2085ea42d011497a6e92e527d123b9b Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8c5ba022f2085ea42d011497a6e92e527d123b9b Commit description: get_perf_callchain() returns a per-CPU perf_callchain_entry buffer and releases its recursion slot via put_callchain_entry() before returning, so nothing keeps the entry reserved while __bpf_get_stack() consumes it below. A preemptible BPF program (e.g. a non-sleepable raw tracepoint program on a PREEMPT kernel, which runs under migrate_disable() but not preempt_disable()) can be scheduled out between obtaining the entry and the copy. Another task scheduled on the same CPU then reuses the same per-CPU buffer and overwrites trace->nr with a larger value. copy_len is then computed from the inflated trace->nr and can exceed the caller's buffer, causing an out-of-bounds write in the memcpy() and in the build_id path. The rcu_read_lock() taken here alone does not prevent this. It is only taken on the may_fault path, and under CONFIG_PREEMPT_RCU it does not disable preemption; it merely keeps perf's callchain buffer array alive (freed via call_rcu()) and does nothing to stop another task from reusing the entry. Disable preemption around obtaining the callchain entry and copying it into the caller's buffer, so the entry cannot be reused underneath us and trace->nr stays bounded by max_depth. Build ID resolution may fault and is therefore deferred until after preemption is re-enabled; by then the instruction pointers have already been copied into buf, so it operates only on that private copy. Note, preempt_disable() also subsumes the buffer-lifetime guarantee the rcu_read_lock() provided, since a preempt-disabled section is an RCU read-side critical section for the callchain buffers' call_rcu() reclaim. Fixes: c195651 ("bpf: add bpf_get_stack helper") Reported-by: Tao Chen Reported-by: STAR Labs SG Signed-off-by: Daniel Borkmann Signed-off-by: Jiri Olsa Signed-off-by: Andrii Nakryiko Cc: stable@vger.kernel.org Link: https://lore.kernel.org/bpf/20260803210149.296496-11-jolsa@kernel.org Signed-off-by: Greg Kroah-Hartman Closes: https://lore.kernel.org/bpf/20260206090653.1336687-1-chen.dylane@linux.dev/ [ changed Fixes: commit ] Changed files: kernel/bpf/stackmap.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=8c5ba022f2085ea42d011497a6e92e527d123b9b ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89580 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89580 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:H/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 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: 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).