From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98524][MODERATE 7.0] rds: ib: Clear the sg list when mapping an MR fails Date: Fri, 23 Oct 2026 20:56:22 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98524 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: 1be3211e6ac77adbb1eac01314d989d243b32c59 List-Id: CVE: CVE-2026-98524 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: rds: ib: Clear the sg list when mapping an MR fails Commit: 1be3211e6ac77adbb1eac01314d989d243b32c59 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1be3211e6ac77adbb1eac01314d989d243b32c59 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98524 Analysis date: Fri, 23 Oct 2026 20:56:22 -0400 ActionableScore: 5 ActionableScore lower bound: unknown Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: A failed RDS IB Fastreg MR mapping can leave a freed scatterlist referenced by a pooled MR, causing a confirmed kernel use after free during later teardown and creating a local denial of service with unresolved privilege escalation potential. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98524 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98524 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-2026-98524 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98524 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=5 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE_KPANIC) 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-416;*CWE-672;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A use after free in the RDS IB Fastreg MR error path occurs because rds_ib_map_frmr can retain a caller owned scatterlist pointer when DMA mapping fails. The caller can then unpin the pages and free the scatterlist while the MR is returned to the pool with the stale pointer still present. A later MR teardown or pool flush can pass the dangling scatterlist to __rds_ib_teardown_mr, and KASAN confirms a slab use after free read in this path. For the CVSS the PR:L reflects that a local user or process must access the RDS RDMA interface and trigger MR registration and cleanup operations. AC:H reflects the additional requirement to reach the DMA mapping failure path and later reuse or tear down the affected pooled MR. The issue is not directly network reachable based on the demonstrated call path even though RDS is a network subsystem. Impact is at least a local denial of service via kernel crash and in the worst case may allow high confidentiality and integrity impact through use after free exploitation and local privilege escalation. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE to IMPORTANT because the CVSS score, vector or bug class threshold rule was applied. KP and FD specialist checks stage IMPORTANT to MODERATE_KPANIC because FD false positive review allowed a downgrade. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were INCREASED_TO_HIGH_BASED_ON_GUESSCVSS and DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH. The independent weaker Aegis shadow evaluated CVSS 2.7 and ActionableScore 5 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE READ UAF DMAorINTERRUPT KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 PrimitiveClass=CLASS_B RealUAF=YES HostAdminRequired=NO NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO RequiresHostUID0=NO AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw conservative score: 5 * Conservative score: 5 * Raw paranoid score: 5 * Paranoid score: 5 * No floor or cap changed either score. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown Positive signals: * +2 Real UAF. A failed DMA mapping leaves `ibmr->sg` referring to a scatterlist subsequently freed by `__rds_rdma_map()`. The stale pointer remains in a pooled MR and is later dereferenced. * +1 Reliable kernel crash or strong DoS. KASAN confirms a slab use-after-free read in `__rds_ib_teardown_mr()`. The same invalid traversal can cause an Oops or kernel crash without KASAN. * +1 Local low-privilege trigger. The supplied assessment identifies PR:L and the commit explicitly identifies possible local privilege escalation through RDS MR operations. * +1 Weak LPE concern. This is more than a generic UAF label because a pooled MR retains a stale structured scatterlist that is later consumed by the teardown path, and the commit explicitly identifies local privilege escalation as a possible consequence. Not awarded: * Controlled reclaim or attacker-shaped replacement contents are not demonstrated. * Arbitrary or directed kernel read/write is not demonstrated. * Strong LPE leverage +2 is not awarded because the supplied evidence does not show controlled reclaim, refcount takeover, callback control, or a completed privilege-escalation chain. * Structured stale-object leverage is not separately awarded because meaningful attacker control of the reclaimed scatterlist contents is unresolved. * No additional Availability point is awarded for the same UAF crash. * Remote reachability is not established merely because RDS is a networking subsystem. * No race penalty applies. This is an ordered mapping-failure and cleanup sequence, not a timing race. * No hardware or niche-subsystem penalty is applied. RDS over InfiniBand is a prerequisite, but rarity and attacker inaccessibility are not sufficiently established. * NEW52 B5-R does not apply because no heap OOB write or retry-accumulated index is present. * NEW53 B3-PENDING does not apply because this is not a shared-backing write. * V33 and V34 do not apply because no attacker-influenced active-state write or checksum-metadata corruption is established. * B4 authorization-state preservation does not apply because no DENY-to-ALLOW authorization decision is changed. * No repeated release/refcount signal exists. The first event frees the caller-owned scatterlist, while the later operation dereferences or tears down stale scatterlist state. It is not a demonstrated second put or refcount mutation on the same lifetime-managed object. * The dedicated repeated-refcount +1 was not awarded. * The paranoid repeated-refcount +1 was not awarded. * FLOOR 5 was not applied because raw arithmetic already reached 5. 3. Reachability analysis The evaluated attacker is a local low-privilege process able to use the RDS RDMA MR interface and invoke the `rds_setsockopt()` lifecycle shown in the trace. The supplied PR:L assessment and explicit local-privilege-escalation statement support below-host-admin reachability, so `HostAdminRequired=NO` and `RequiresHostUID0=NO`. The complete namespace capability model is not shown. RDS socket namespace awareness does not prove that all RDMA device, MR registration, mapping-failure, and teardown stages are available inside an attacker-created namespace, so `NamespaceScopedPrivilege=UNKNOWN`. The vulnerable path requires RDS over InfiniBand or compatible RDMA support, an MR mapping attempt, DMA mapping or later registration failure, return of the affected MR to its pool, and subsequent MR teardown or pool flushing. Existing RDS and RDMA configuration may constitute prior administrative setup, but the attacker does not need to configure the host to exercise an already exposed interface. No timing race is required. Reliability of forcing `ib_dma_map_sg()` failure remains unresolved and limits trigger confidence, but it does not erase the confirmed UAF. The issue is not directly remotely triggerable based on the supplied call path. Network traffic alone is not shown to create and free the affected local MR. 4. Primitive and severity interpretation The exact primitive is a stale pointer to a freed scatterlist retained in an MR object after mapping failure. The MR survives in a reusable pool, while the caller unpins the associated pages and frees the scatterlist. A later teardown follows `ibmr->sg` after its lifetime has ended, producing a confirmed slab use-after-free read. This is an active structured-object lifetime violation rather than fixed asynchronous stale storage. However, the demonstrated use occurs in MR teardown and the supplied evidence does not show controlled reclamation or attacker-controlled replacement contents. It is therefore CLASS_B rather than CLASS_A. This is category A, an ordinary stale cleanup dereference, rather than category B, a concrete second release or refcount mutation through the exact dangling object. The later teardown may perform operations based on stale scatterlist fields, but no second lifetime mutation of the scatterlist object itself is established. Demonstrated consequences are a KASAN-detected UAF and plausible kernel crash. Possible local privilege escalation is explicitly identified, but the concrete exploitation mechanism beyond stale structured traversal remains unresolved. That unresolved LPE concern is sufficient for `ImportantCandidate=YES`, mandatory review, and `AutoDowngradeAllowed=NO`, but not sufficient to claim arbitrary kernel access or CLASS_A. Operationally, this is at least Actionable Moderate. Important severity remains a credible candidate because the dangling scatterlist survives in a pool and later enters privileged RDMA teardown processing, but stronger impact requires review of reclaim control, SG traversal, DMA unmapping behavior, and attacker control over the failed mapping sequence. 5. One-sentence report phrase A failed RDS IB Fastreg MR mapping can leave a freed scatterlist referenced by a pooled MR, causing a confirmed kernel use after free during later teardown and creating a local denial of service with unresolved privilege escalation potential. 6. Manual review recommendation MANUAL CHECK REQUIRED The UAF is confirmed, the stale pointer survives in a pooled kernel object, and the commit explicitly identifies possible local privilege escalation, while reclaim control and the exact post-free exploitation primitive remain unresolved. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: rds: ib: Clear the sg list when mapping an MR fails Commit: 1be3211e6ac77adbb1eac01314d989d243b32c59 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1be3211e6ac77adbb1eac01314d989d243b32c59 Commit description: rds_ib_map_frmr() stores the caller's scatterlist in the MR before DMA mapping and registration can fail. On failure, __rds_rdma_map() unpins the pages and frees the scatterlist, but rds_ib_free_frmr() can still return the MR to the pool with the stale pointer set. This leaves the pool with a dangling scatterlist and can lead to local privilege escalation. KASAN detects the resulting use-after-free when the MR is later torn down: BUG: KASAN: slab-use-after-free in __rds_ib_teardown_mr Read of size 8 Call Trace: __rds_ib_teardown_mr rds_ib_unreg_frmr rds_ib_flush_mr_pool rds_ib_flush_mrs rds_free_mr rds_setsockopt Store the scatterlist in the MR only after DMA mapping succeeds. If DMA mapping fails, return directly while the MR fields remain clear; the caller keeps ownership of the scatterlist and its pinned pages. If a later registration step fails, unmap the scatterlist and clear the MR fields before returning. Fixes: 1659185 ("RDS: IB: Support Fastreg MR (FRMR) memory registration mode") Cc: stable@vger.kernel.org Signed-off-by: Dongliang Qin Reviewed-by: Allison Henderson Link: https://patch.msgid.link/20260922031546.3874605-1-cccccccccccc777777@gmail.com Signed-off-by: Paolo Abeni Signed-off-by: Greg Kroah-Hartman Changed files: net/rds/ib_frmr.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=1be3211e6ac77adbb1eac01314d989d243b32c59 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98524 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98524 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: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).