From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98242][MODERATE REGULAR] dma-buf: Fix silent overflow for phys vec to sgt Date: Fri, 09 Oct 2026 13:40:44 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98242 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: 2 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 6b98fd7106d4e486f432664893dcd4d6fa3a9693 List-Id: CVE: CVE-2026-98242 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: dma-buf: Fix silent overflow for phys vec to sgt Commit: 6b98fd7106d4e486f432664893dcd4d6fa3a9693 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6b98fd7106d4e486f432664893dcd4d6fa3a9693 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98242 Analysis date: Fri, 09 Oct 2026 13:40:44 -0400 ActionableScore: 2 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98242 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98242 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: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-98242 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98242 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 LEGACY=MODERATE RESULT=DIFF (independent Legacy and Aegis differ; FINAL: MODERATE, Aegis: 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:L/I:L/A:H';CWE-190;CWE-681;CWE-682;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '5.8';DESCR 'A 32 bit overflow in mapped_len can silently truncate the accumulated length when a peer to peer DMA mapping through a host bridge exceeds 4 GB. The resulting scatter gather table can describe less memory than the original IOVA mapping and can pass truncated lengths to fill_sg_entry. This may cause incomplete or incorrect DMA transfers, IOMMU faults, device failures, or system availability impact depending on how the consuming driver uses the table. For the CVSS the PR:L value is used for the paranoid score because a local process with access to an affected device interface may be able to request DMA operations without having full host administrative privileges. AC:H is appropriate because exploitation requires a specific hardware and routing configuration with MMIO larger than 4 GB and peer to peer DMA crossing a host bridge. The issue is not directly network reachable. Impact is at least incorrect DMA mapping behavior and in the worst defensible case may include limited confidentiality or integrity impact with high availability impact. The DMA memory boundary makes this issue suitable for manual review even though an arbitrary write primitive is not established.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) MAYBE DANGER SIMPLEFIX DMAorINTERRUPT MEMORY DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 2 * Conservative score: 2 * Raw paranoid score: 2 * Paranoid score: 2 * No floor or cap applied. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +1 Memory-layout invariant restoration. A 32-bit `mapped_len` truncates an accumulated `size_t` IOVA length above 4 GB, producing SG lengths inconsistent with the actual mapping. * +1 Weak indirect corruption candidate. The truncated value is consumed by `fill_sg_entry()` to construct active DMA scatter-gather descriptors. This establishes malformed descriptor state, but not an OOB write or arbitrary DMA target. * 0 Reliable kernel crash. The patch does not establish a host crash, panic, or filesystem-wide failure. * 0 Confidentiality or integrity impact. No disclosure, unauthorized protected-state modification, expanded mapping, or attacker-directed DMA write is demonstrated. * 0 Hardware penalty. MMIO above 4 GB and peer-to-peer DMA through a host bridge are explicit prerequisites, but the supplied evidence does not prove that the required hardware is sufficiently rare for a penalty. * 0 Privilege penalty. The complete caller and userspace access path are absent, so host-admin privilege cannot be positively established. * B5-R does not apply. There is no confirmed heap OOB write, retry-accumulated index, attacker-influenced retry sequence, or later consumption of retry-corrupted heap state. * Controlled target selection, arbitrary write, UAF, controlled reclaim, and privilege escalation are not demonstrated. * The `calc_sg_nents()` overflow is described as a similar potential issue. The supplied evidence does not establish that it previously caused a concrete undersized allocation followed by an OOB write. 3. Reachability analysis The vulnerable helper processes physical-vector and IOVA mappings in the DMA-BUF subsystem. Triggering requires an MMIO mapping larger than 4 GB and peer-to-peer DMA routed through a host bridge. The supplied context does not identify the callers or establish whether an ordinary render-node client, another unprivileged device user, a delegated service, or only a host administrator can create the complete mapping. Therefore `HostAdminRequired` and namespace-scoped reachability remain unknown. A compatible device and topology are prerequisites. No network trigger, retry race, or attacker-controlled retry loop is established. The operation is deterministic once the oversized mapping reaches this path. 4. Primitive and severity interpretation The exact primitive is integer truncation that produces undersized SG entry lengths and potentially an overflowed SG-entry count. This is malformed active DMA descriptor state, not a confirmed heap overwrite, UAF, double release, or authorization bypass. The demonstrated result is incorrect mapping representation. Plausible consequences include incomplete DMA transfers, IOMMU faults, device failure, or device-local availability loss. Host-wide failure and memory corruption are not established. This remains `CLASS_C` because no independently useful write, disclosure, ownership violation, or lifetime primitive is shown. `ImportantCandidate=NO` follows because the mandatory B5-R conditions are not met and no Class A or strong Class B primitive exists. `AutoDowngradeAllowed=YES` because the available evidence supports an ordinary malformed-state issue rather than unresolved Important-grade corruption. 5. One-sentence report phrase A 32-bit length truncation can produce malformed scatter-gather descriptors for DMA mappings larger than 4 GB, but the supplied evidence does not establish an out-of-bounds write, host-wide crash, or attacker-controlled memory-corruption primitive. 6. Manual review recommendation MANUAL CHECK RECOMMENDED Review callers of `dma_buf_phys_vec_to_sgt()` to determine userspace reachability and whether any consumer trusts the original size beyond the generated SG length, which could establish an OOB DMA operation or stronger availability impact. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: dma-buf: Fix silent overflow for phys vec to sgt Commit: 6b98fd7106d4e486f432664893dcd4d6fa3a9693 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6b98fd7106d4e486f432664893dcd4d6fa3a9693 Commit description: In case MMIO size is bigger than 4G and peer2peer DMA goes through host bridge, we trigger a code path that assigns the total linked IOVA (which is greater than 4G) to mapped_len. Previously, `mapped_len` was declared as 32-bit `unsigned int`. When accumulating `size_t` lengths, this leads to a silent wrap-around. This truncation causes truncated lengths to be passed to functions like `fill_sg_entry()`. Fix this by changing `mapped_len` to `size_t` (64-bit). While at it, fix similar potential overflow issues in `calc_sg_nents` by using `check_add_overflow()` for `nents` and using `unsigned int` for the loop iterator in `fill_sg_entry` to match. Fixes: 3aa31a8 ("dma-buf: provide phys_vec to scatter-gather mapping routine") Cc: stable@vger.kernel.org Cc: iommu@lists.linux.dev Reviewed-by: Pranjal Shrivastava Reviewed-by: Kevin Tian Reviewed-by: Leon Romanovsky Signed-off-by: David Hu Signed-off-by: Christian König Link: https://lore.kernel.org/r/20260901170849.4052816-2-dhu@x6u.co Signed-off-by: Greg Kroah-Hartman Changed files: drivers/dma-buf/dma-buf-mapping.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=6b98fd7106d4e486f432664893dcd4d6fa3a9693 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98242 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98242 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:N/I:L/A:L The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS score: 5.8 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: 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).