From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-80987][LOW] NTB: ntb_transport: Reject oversized TX buffers Date: Fri, 11 Sep 2026 19:38:16 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-80987 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: 2 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: a7f22105a7df8c7fd74d0af27ace6fa94fe03d87 List-Id: CVE: CVE-2026-80987 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: NTB: ntb_transport: Reject oversized TX buffers Commit: a7f22105a7df8c7fd74d0af27ace6fa94fe03d87 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a7f22105a7df8c7fd74d0af27ace6fa94fe03d87 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80987 Analysis date: Fri, 11 Sep 2026 19:38:16 -0400 ActionableScore: 2 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: NTB transport incorrectly treated oversized TX buffers as successful, causing ntb_netdev to miss skb cleanup and allowing repeated oversized transmissions to leak memory and potentially cause local resource exhaustion DoS. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80987 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80987 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-2026-80987 LOW https://www.kernelcve.org/list/?q=CVE-2026-80987 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:H';*CWE-401;*CWE-772;**CWE-400;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'NTB transport handled an oversized TX buffer by calling tx_handler() with a NULL data pointer and then returning success. For ntb_netdev this can bypass both normal completion cleanup and the enqueue error path, so the skb is not freed and memory can leak on each oversized transmit attempt. For the CVSS the PR:L is used because reliable triggering normally requires a local user or process able to send traffic through the NTB backed netdev or otherwise enqueue TX buffers on the victim. The issue is not directly Internet reachable. Remote influence is only plausible in special routing or bridging setups where untrusted traffic is forwarded into the NTB netdev. Impact is denial of service through resource exhaustion after repeated oversized transmissions. No memory corruption or privilege escalation primitive is indicated by the patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) YES INIT SIMPLEFIX LEAK ERRORPATH SKB INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES ## 1. ActionableScore * Raw conservative score: 2 * Conservative score: 2 * Raw paranoid score: 2 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate**:: No floor or cap changed the score. ## 2. Signal breakdown Positive signals: * +1 Concrete persistent kernel resource/reference leak. The patch establishes that an oversized TX skb can be leaked because `ntb_process_tx()` returned success after calling `tx_handler()` with NULL data, so `ntb_netdev` did not free the skb through either normal completion or enqueue error handling. * +1 Local below-host-admin runtime trigger. Once an NTB-backed netdev is configured and usable, a local process that can send traffic through it may trigger the oversized TX path. This is not host-admin-equivalent driver management. Negative or non-awarded signals: * 0 Real UAF not awarded. No stale object use, post-free dereference, double free, or repeated release/refcount mutation is established. * 0 Memory corruption not awarded. The defect is a lost skb cleanup path, not an overwrite, UAF, OOB access, or type confusion. * 0 Reliable kernel crash not awarded. The demonstrated consequence is a leak with possible resource exhaustion, not immediate panic or Oops. * 0 Extra availability not awarded. Repeated leaks may cause DoS, but that is the same resource-leak consequence already counted. * 0 Confidentiality and integrity not awarded. No disclosure, unauthorized write, privilege escalation, or security-boundary bypass is supported. * 0 Remote reachability not awarded. The bug is not directly Internet reachable. Remote influence would require special forwarding or bridging into the NTB netdev and is not established. * 0 Rare hardware penalty not applied. NTB is specialized hardware, but the scoring rules require concrete evidence before subtracting for rarity. Repeated release/refcount check: * First release can end lifetime: no such first release is shown. * Exact same reference survives: not applicable. * Second operation mutates lifetime/refcount: no. * Concrete repeated release/refcount +1 awarded: no. * Paranoid repeated-refcount leverage +1 awarded: no. * FLOOR 5 applied: no. ## 3. Reachability analysis The practical trigger is local traffic transmission through an NTB-backed network device. A host administrator or system setup normally must provision the NTB device and interface, but the vulnerable operation itself is in the runtime TX enqueue path. Therefore HostAdminRequired is NO for an already configured victim, while prior privileged setup may exist operationally. No namespace-scoped capability chain is established. This is not a netns-created virtual object path, and the NTB device is hardware-backed. NamespaceScopedPrivilege is NO. The issue is not directly network-triggerable from the Internet. A remote packet could matter only if the deployment forwards or bridges untrusted traffic into the NTB-backed netdev and can produce oversized TX buffers. That is a deployment-specific indirect path, not a patch-established remote vector. No race is involved. No special timing is required. The issue is an ordered error-handling and ownership bug. ## 4. Primitive and severity interpretation The exact primitive is a persistent skb memory leak caused by incorrect success reporting for oversized TX buffers. The caller loses the normal ownership/cleanup decision because `ntb_process_tx()` reports success even though the buffer was not transmitted and the skb was not freed. This is not active structured-object UAF and not fixed stale storage UAF. It is a resource-management bug. There is no concrete repeated lifetime/refcount mutation on the same dangling object. PrimitiveClass is CLASS_C because the demonstrated behavior is resource exhaustion / DoS without an independently useful corruption primitive. The demonstrated consequence is memory pressure from repeated leaked skb objects. The speculative consequence is broader system DoS if the leak is repeated enough. No privilege escalation, arbitrary read/write, or information leak is supported. ImportantCandidate is NO because there is no UAF, no memory corruption, no ownership/COW violation, no authorization bypass, and no unresolved Important-grade primitive. AutoDowngradeAllowed is YES because this is a constrained resource leak with no meaningful unresolved exploitation leverage beyond DoS. Likely operational severity is Low to ordinary Moderate, depending on whether untrusted local or forwarded traffic can repeatedly hit the NTB TX path. ## 5. One-sentence report phrase NTB transport incorrectly treated oversized TX buffers as successful, causing ntb_netdev to miss skb cleanup and allowing repeated oversized transmissions to leak memory and potentially cause local resource exhaustion DoS. ## 6. Manual review recommendation NO MANUAL CHECK NEEDED Reason: this is a concrete skb memory leak/resource exhaustion issue without UAF, memory corruption, authorization bypass, remote reachability, or privilege escalation evidence. ## 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: NTB: ntb_transport: Reject oversized TX buffers Commit: a7f22105a7df8c7fd74d0af27ace6fa94fe03d87 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a7f22105a7df8c7fd74d0af27ace6fa94fe03d87 Commit description: ntb_process_tx() handles an oversized buffer by calling tx_handler() with a NULL data pointer and returning success. ntb_netdev therefore neither frees the skb in its completion callback nor takes its enqueue error path, leaking it. Reject oversized buffers in ntb_transport_tx_enqueue() before acquiring a queue entry and return -EMSGSIZE. The caller retains ownership of the buffer, and the preceding netdev patch frees the skb when enqueue returns this permanent error. Fixes: fce8a7b ("PCI-Express Non-Transparent Bridge Support") Cc: stable@vger.kernel.org Signed-off-by: Koichiro Den Reviewed-by: Dave Jiang Link: https://patch.msgid.link/20260817053519.4135287-5-den@valinux.co.jp Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman Changed files: drivers/ntb/ntb_transport.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=a7f22105a7df8c7fd74d0af27ace6fa94fe03d87 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80987 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80987 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:L/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 5.5 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: 2 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).