From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-99164][IMPORTANT] spi: imx: fix slab corruption from undersized DMA bounce buffers Date: Fri, 30 Oct 2026 11:00:43 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-99164 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: 4 X-AL-KERNEL-Commit: 2777f6637da02da84c9c1ff92f413ce0f0995084 List-Id: CVE: CVE-2026-99164 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: spi: imx: fix slab corruption from undersized DMA bounce buffers Commit: 2777f6637da02da84c9c1ff92f413ce0f0995084 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2777f6637da02da84c9c1ff92f413ce0f0995084 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99164 Analysis date: Fri, 30 Oct 2026 11:00:43 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: An undersized i.MX SPI DMA bounce-buffer allocation causes confirmed adjacent-slab writes that corrupted an active RPMSG endpoint refcount and eventually produced a kernel oops. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99164 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99164 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: IMPORTANT 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-2026-99164 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-99164 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=3 LEGACY=IMPORTANT RESULT=DIFF INDEPENDENT_LEGACY=IMPORTANT INDEPENDENT_RESULT=DIFF TEMP_KPANIC_MERGE=IMPORTANT_WINS_DISAGREEMENT PRE_MERGE_LEGACY=IMPORTANT (final Legacy and Aegis differ; FINAL: IMPORTANT, Aegis: MODERATE_KPANIC) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';CWE-131;*CWE-787;CWE-122;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'The SPI i.MX driver allocated DMA TX and RX bounce buffers using dma_len but mapped and synchronized them using the larger DMA_CACHE_ALIGNED_LEN value. The DMA API therefore accessed memory beyond the slab allocation, and testing confirmed corruption of a neighboring rpmsg endpoint refcount followed by use after free warnings and a kernel paging oops. This is a concrete out of bounds memory corruption issue with at least kernel denial of service impact and a plausible but unproven path to confidentiality or integrity impact through corrupted kernel objects. For the CVSS the PR:L base value reflects a local process or subsystem able to initiate the affected SPI transfers. For the CVSS the PR:N paranoid value applies only when attacker controlled traffic from an attached CAN or similar peripheral can repeatedly drive the vulnerable SPI path lacking a local user context. The issue is not directly reachable through an ordinary IP network and reliable exploitation has high complexity because it depends on slab placement, workload, cache alignment, and timing. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 7.5 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_KPANIC to IMPORTANT because the CVSS score, vector or bug class threshold rule was applied. KP and FD specialist checks stage IMPORTANT to IMPORTANT because a specific evidence based protection or manual review veto was applied. 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 V42_LEGACY_CLASSA_FD_VETO and MANUAL_REVIEW_REQUIRED and TEMP_KPANIC_MERGE_IMPORTANT_WINS. The independent weaker Aegis shadow evaluated CVSS 2.5 and ActionableScore 3 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is IMPORTANT.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE OOB LEAK UAF DMAorINTERRUPT HARDWARE KPANIC MEMORY KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS V42_LEGACY_CLASSA_FD_VETO MANUAL_REVIEW_REQUIRED TEMP_KPANIC_MERGE_IMPORTANT_WINS - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=4 PrimitiveClass=CLASS_A 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 base score: 4. * Conservative score: 4; no floor or cap applied. * Raw paranoid score: 5. * Paranoid score: 5; adds only technically credible peripheral-mediated influence. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown * +2 confirmed heap/slab out-of-bounds write: buffers allocated at `dma_len` are mapped and synchronized at the larger cache-aligned length; an adjacent `rpmsg_endpoint` refcount was observed changing from 2 to 1 during the resulting memcpy. * +1 high-value active-state corruption: the overwritten field is lifetime/refcount state, subsequently consumed by `kref_get`/`kref_put` processing. * +1 reliable kernel crash/strong DoS: refcount underflow/saturation warnings culminated in a paging-request oops. * Paranoid +1 firmware/device-mediated influence: traffic delivered through an attached CAN-like peripheral can credibly drive repeated SPI transfers, but malicious control of that complete path is not established. * No separate Availability point: the oops and availability loss are the same effect. * No confidentiality, integrity-impact, arbitrary-write, controlled-target, controlled-reclaim, or LPE bonus. * `RealUAF=NO`: refcount diagnostics contain “use-after-free” wording and early lifetime termination is plausible, but the supplied call path does not prove a specific stale post-free dereference. * B5-R does not apply: no retry-accumulated index/offset or missing retry reset is shown. 3. Reachability analysis The vulnerable operation occurs in i.MX ECSPI DMA transfers and requires affected hardware plus an attached SPI peripheral. Heavy CAN/RPMSG workload demonstrably triggers it, but the evidence does not establish whether an ordinary local user, a remote CAN participant, firmware, or only a privileged subsystem controller can initiate the complete sequence. Therefore host-admin and namespace privilege remain unknown. No namespace-scoped capability path is shown. The 30-minute to 30-hour reproduction window indicates low reliability, but repeated workload reaches the defect naturally; no separate narrow race penalty is applied. 4. Primitive and severity reading The exact primitive is a heap OOB DMA/cache-maintenance write caused by allocation-versus-map/sync length mismatch. It has demonstrably overwritten adjacent active structured lifetime state, which later refcount operations consume. This is stronger than a speculative bounds defect or guard-only detection and supports CLASS_A, although target selection and useful payload control are unproven. The shown consequence is refcount corruption followed by kernel failure. Exploitable object-lifetime manipulation, disclosure, or privilege escalation remains speculative. ImportantCandidate is retained because a concrete adjacent-object write reached active refcount state and exploit leverage requires human analysis. Auto-downgrade is disallowed despite uncertain attacker reachability. 5. One-sentence report phrase An undersized i.MX SPI DMA bounce-buffer allocation causes confirmed adjacent-slab writes that corrupted an active RPMSG endpoint refcount and eventually produced a kernel oops. 6. Manual review advice MANUAL CHECK REQUIRED Determine who can drive the affected SPI transfer workload and whether peripheral-controlled data or allocator shaping provides useful control over the adjacent-object corruption. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: spi: imx: fix slab corruption from undersized DMA bounce buffers Commit: 2777f6637da02da84c9c1ff92f413ce0f0995084 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2777f6637da02da84c9c1ff92f413ce0f0995084 Commit description: Since commit faa8e40 ("spi: imx: support dynamic burst length for ECSPI DMA mode"), the driver allocates its private DMA TX/RX buffers with kzalloc(dma_len), where dma_len is only rounded up to 4 bytes, but maps, syncs and unmaps them with DMA_CACHE_ALIGNED_LEN(dma_len), i.e. rounded up to the cache line size. As a result, the DMA API operates on memory beyond the end of the allocation. This was observed on a custom i.MX8MP platform with an mcp251xfd CAN controller under heavy RPMSG load, as a series of refcount_t warnings triggered from rpmsg_recv_done() in virtio_rpmsg_bus: refcount_t: addition on 0; use-after-free. refcount_t: underflow; use-after-free. refcount_t: saturated; leaking memory. Leading finally to an "Unable to handle kernel paging request" oops. Reproducing this problem took between 30 minutes and roughly 30 hours under the same workload. Hardware watchpoints on the refcount of a struct rpmsg_endpoint showed it was overwritten from 2 to 1 by __pi_memcpy_generic() in the irq/155-spi2.0 thread. Additionally it was found that a "normal" rpmsg_recv_done() took 11µs +/-2µs from its kref_get to kref_put. In the error case the same sequence took about 215µs +/-10µs. Based on this, an LLM was used to identify the size mismatch fixed here. Allocate the buffers with DMA_CACHE_ALIGNED_LEN(dma_len) so they cover the full mapped length, and use the same length for dma_sync_single_for_cpu() to stay consistent with map and unmap. With this patch applied, the same workload ran for more than 200 hours without the problem reproducing. Assisted-by: LLM Fixes: faa8e40 ("spi: imx: support dynamic burst length for ECSPI DMA mode") Cc: stable@vger.kernel.org Signed-off-by: Richard Leitner Link: https://patch.msgid.link/20261015-fix-spi-imx-dma-v1-1-e28259671392@linux.dev Signed-off-by: Mark Brown Signed-off-by: Greg Kroah-Hartman Changed files: drivers/spi/spi-imx.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=2777f6637da02da84c9c1ff92f413ce0f0995084 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-99164 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99164 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:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 7.5 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: 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: IMPORTANT KPANIC detected for this report: YES Published priority for this report (same as in Subject): IMPORTANT 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).