From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-64281][MODERATE REGULAR] svcrdma: wake sq waiters when the transport closes Date: Sat, 25 Jul 2026 10:19:40 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-64281 X-AL-KERNEL-Priority: MODERATE REGULAR X-AL-KERNEL-Severity: MODERATE REGULAR X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 4 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: 40eedc4253dbda0b29b7961200534dfcecb48ace List-Id: CVE: CVE-2026-64281 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: svcrdma: wake sq waiters when the transport closes Commit: 40eedc4253dbda0b29b7961200534dfcecb48ace Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=40eedc4253dbda0b29b7961200534dfcecb48ace Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64281 Analysis date: Sat, 25 Jul 2026 10:19:40 -0400 ActionableScore: 4 ActionableScore lower bound: 3 Actionable bucket: Borderline manual review recommended, not Important Manual review required: YES Summary: An NFS/RDMA remote disconnect or completion error can leave SQ waiters stuck in svc_rdma_sq_wait, pinning transport references and blocking teardown, resulting in a persistent denial of service without evidence of memory corruption or privilege escalation. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64281 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64281 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 REGULAR 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-2026-64281 MODERATE CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';*CWE-833;CWE-667;**CWE-400;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.5';DESCR 'An NFS/RDMA transport close can leave threads parked in svc_rdma_sq_wait because the close path sets XPT_CLOSE but does not wake sc_sq_ticket_wait or sc_send_wait. A remote RDMA disconnect or RDMA completion error can therefore leave workers in TASK_UNINTERRUPTIBLE state, pin svc_xprt references, and block svc_rdma_free from completing. For the CVSS the PR:N is used because an attacker does not need local user access on the victim when the NFS/RDMA endpoint is reachable from the RDMA fabric. The issue is adjacent network reachable in typical storage or data center RDMA deployments rather than public Internet reachable. Impact is denial of service through stuck kernel worker threads and blocked transport teardown. For the paranoid score, choose the highest still-defensible interpretation supported by the bug class and patch context, with preference for manual-review sensitivity over autoclosed false negatives. The patch context does not support memory corruption or privilege escalation, so confidentiality and integrity remain none.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended, not Important (with actual score 4) SKIP CVE-2026-64281 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: ccc89b9d1ed233349cfe8d87b842e7351b74d8de YES NO NO unknown MAYBE LOCK ERRORPATH HARDWARE INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=3 ## 1. ActionableScore * Conservative score: 3 * Paranoid score: 4 * Final recommended bucket: **Borderline manual review recommended, not Important**:: ## 2. Signal breakdown Triggered signals: * Remote reachable / network-triggerable: +2 A remote RDMA disconnect reaches `svc_rdma_cma_handler()` and previously called `svc_xprt_deferred_close()` without waking RDMA SQ waiters. * Reliable kernel crash / strong DoS: +1 This is not a crash, but it is a strong service DoS: worker threads can remain in `TASK_UNINTERRUPTIBLE`, pin `svc_xprt` references, and block `svc_rdma_free()`. * Availability impact realistic: +1 in paranoid score The impact can persist beyond a transient failure because references remain pinned and teardown can block indefinitely, especially if all workers are parked. Subtracted or limited signals: * Rare / configuration-dependent exposure: -1 in conservative score NFS/RDMA requires RDMA-capable deployment and is typically limited to storage or data-center fabrics, not public Internet exposure. Not applied: * No memory corruption signal The patch fixes missing wakeups and stuck waiters. It does not show UAF, double-free, OOB access, type confusion, arbitrary write, or stale callback execution. * No privilege escalation signal The retained references prevent teardown rather than creating attacker-controlled reuse or corruption. * No confidentiality or integrity impact The patch context supports availability impact only. Call-site confidence: high. The patch shows all converted close/error paths and the added wakeups. ## 3. Reachability analysis A remote peer on the RDMA fabric can trigger relevant close paths through disconnects or RDMA completion errors. No local user access on the victim is required once the NFS/RDMA endpoint is reachable. This is adjacent-network rather than general Internet exposure. Namespaces and containers do not materially lower or raise the attacker privilege requirement for the remote case. Local administrative setup is required to run NFS/RDMA, but that is deployment configuration, not attacker privilege. The path is not default-enabled on ordinary Linux systems because it requires NFS/RDMA and RDMA infrastructure. In environments where NFS/RDMA is used, the bug is reachable through normal transport teardown and error handling. ## 4. Severity interpretation This behaves like an actionable Moderate DoS issue, not an Important-class memory-corruption vulnerability. The theoretical risk is bounded by the observed primitive: missing wakeups cause stuck waiters and reference pinning. There is no evidence of attacker-controlled reclaim, writable stale object access, callback corruption, refcount takeover, or privilege escalation. The conservative score is lower because NFS/RDMA is deployment-specific. The paranoid score is higher because the trigger can be remote within an RDMA fabric and the hang can persist across transport teardown. ## 5. One-sentence report phrase An NFS/RDMA remote disconnect or completion error can leave SQ waiters stuck in svc_rdma_sq_wait, pinning transport references and blocking teardown, resulting in a persistent denial of service without evidence of memory corruption or privilege escalation. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: the issue is remotely reachable in NFS/RDMA deployments and can cause persistent service degradation or teardown hangs, but it should be reviewed as DoS-only unless additional evidence shows a memory lifetime or corruption primitive. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: svcrdma: wake sq waiters when the transport closes Commit: 40eedc4253dbda0b29b7961200534dfcecb48ace Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=40eedc4253dbda0b29b7961200534dfcecb48ace Commit description: Threads parked in svc_rdma_sq_wait() on sc_sq_ticket_wait or sc_send_wait can hang indefinitely in TASK_UNINTERRUPTIBLE state across transport teardown, pinning svc_xprt references and blocking svc_rdma_free(). The close path sets XPT_CLOSE before invoking xpo_detach and both wait_event predicates include an XPT_CLOSE term, but the predicates are re-evaluated only on wakeup. sc_sq_ticket_wait has no completion-driven wake path; it is advanced solely by the chained ticket handoff inside svc_rdma_sq_wait() itself. Without an explicit wake at close, parked threads never observe XPT_CLOSE, hold their svc_xprt_get reference forever, and svc_rdma_free() blocks on xpt_ref dropping to zero. Two close entry points reach this transport. Local teardown runs svc_rdma_detach() from svc_handle_xprt() -> svc_delete_xprt() -> xpo_detach() on a worker thread. A remote disconnect arrives at svc_rdma_cma_handler(), which calls svc_xprt_deferred_close(): that sets XPT_CLOSE and enqueues the transport but does not access either RDMA waitqueue, so a worker already parked in svc_rdma_sq_wait() never re-evaluates its predicate. With every worker parked on this transport, no thread is available to run the local teardown either, and the wake site there is unreachable. Introduce svc_rdma_xprt_deferred_close(), a thin svcrdma wrapper that calls svc_xprt_deferred_close() and then wakes both sc_sq_ticket_wait and sc_send_wait. Convert the svcrdma producers that called svc_xprt_deferred_close() directly: svc_rdma_cma_handler(), qp_event_handler(), svc_rdma_post_send_err(), svc_rdma_wc_send(), the sendto drop path, the rw completion error paths, and the recvfrom flush and read-list error paths. Wake both waitqueues from svc_rdma_detach() as well. The synchronous svc_xprt_close() path (backchannel ENOTCONN, device removal via svc_rdma_xprt_done) reaches detach without flowing through svc_xprt_deferred_close() and therefore does not invoke the new helper. Fixes: ccc89b9 ("svcrdma: Add fair queuing for Send Queue access") Cc: stable@vger.kernel.org Assisted-by: kres (claude-opus-4-7) Signed-off-by: Chris Mason [ cel: add svc_rdma_xprt_deferred_close() to complete the fix ] Signed-off-by: Chuck Lever Signed-off-by: Greg Kroah-Hartman Changed files: include/linux/sunrpc/svc_rdma.h net/sunrpc/xprtrdma/svc_rdma_recvfrom.c net/sunrpc/xprtrdma/svc_rdma_rw.c net/sunrpc/xprtrdma/svc_rdma_sendto.c net/sunrpc/xprtrdma/svc_rdma_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=40eedc4253dbda0b29b7961200534dfcecb48ace ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64281 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64281 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:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 6.5 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: 3 Paranoid ActionableScore: 4 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: NO Published priority for this report (same as in Subject): MODERATE REGULAR 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).