* [CVE-2026-98242][MODERATE REGULAR] dma-buf: Fix silent overflow for phys vec to sgt
@ 2026-10-09 17:40 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-09 17:40 UTC (permalink / raw)
To: kernel-cve
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: [email protected]
Cc: [email protected]
Reviewed-by: Pranjal Shrivastava <[email protected]>
Reviewed-by: Kevin Tian <[email protected]>
Reviewed-by: Leon Romanovsky <[email protected]>
Signed-off-by: David Hu <[email protected]>
Signed-off-by: Christian König <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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