From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-63929][LOW] iio: buffer: Fix DMA fence leak in iio_buffer_enqueue_dmabuf() Date: Sun, 19 Jul 2026 19:37:09 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-63929 X-AL-KERNEL-Priority: LOW X-AL-KERNEL-Severity: LOW X-AL-KERNEL-Base-Severity: LOW X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 2 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 9678aeed8b77d495a417dd057d479f3733094019 List-Id: CVE: CVE-2026-63929 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: iio: buffer: Fix DMA fence leak in iio_buffer_enqueue_dmabuf() Commit: 9678aeed8b77d495a417dd057d479f3733094019 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9678aeed8b77d495a417dd057d479f3733094019 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63929 Analysis date: Sun, 19 Jul 2026 19:37:09 -0400 ActionableScore: 2 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate / Low-like Manual review required: NO Summary: A local DMA fence reference leak in the IIO DMABUF enqueue path can leak one kmalloc-128 object per successful enqueue, allowing sustained local use of the device interface to cause memory exhaustion and denial of service. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-63929 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63929 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: LOW 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-2026-63929 LOW CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-401;*CWE-772;**CWE-400;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'A DMA fence reference leak in the IIO DMABUF enqueue path occurs because iio_buffer_enqueue_dmabuf() adds the fence to the DMA reservation object but does not drop the initial reference from dma_fence_init(). Each successful enqueue can therefore leak one small kmalloc allocation, and repeated high rate buffer enqueue operations can cause slab growth and eventual memory exhaustion. For the CVSS the PR:L is used because a local process needs access to the affected IIO device and DMABUF enqueue interface, but full administrator privileges are not necessarily required in practical deployments. The issue is not network reachable and is triggered through a local device interface rather than packet traffic. Impact is denial of service through resource exhaustion. For the paranoid score, the highest still defensible interpretation is availability high because sustained enqueues can exhaust memory, but the vulnerability class remains resource leak only.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) SKIP CVE-2026-63929 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 3e26d9f08fbe0b73e951a5e810fdb7a332b7e37f YES NO NO unknown MAYBE LEAK DMAorINTERRUPT IMPROVEONLY LINUS TEST MEMORY DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 ## 1. ActionableScore * Conservative score: 2 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate / Low-like** ## 2. Signal breakdown Triggered signals: * Local trigger: +1 A local process with access to the affected IIO DMABUF enqueue interface can repeatedly enqueue buffers. * Availability impact realistic: +1 Each successful enqueue leaks one small kmalloc-128 DMA fence allocation. Sustained high-rate use can cause slab growth and eventual memory pressure or resource exhaustion. Not triggered: * No remote/network reachability. * No generic memory corruption. This is a reference leak, not UAF, double-free, OOB write, type confusion, or arbitrary write. * No privilege escalation primitive is shown. * No confidentiality or integrity impact is supported. * No security-boundary bypass is shown. * No high-control API bonus. The interface is device-specific and the patch does not show attacker control over object reuse, callback targets, refcounts beyond the leaked reference, or memory layout. ## 3. Reachability analysis The bug is reachable from a local process that can access the relevant IIO device and use the DMABUF buffer enqueue path. This may be unprivileged in deployments where device permissions expose the IIO interface to users or service accounts, but it is not a generic unprivileged syscall path. Namespaces or containers only matter if the device node or IIO interface is delegated into them. The path is not network reachable and is not a default broad kernel attack surface on ordinary systems. Call-site confidence: high, because the patch and commit message describe the exact allocation, reference transfer, missing dma_fence_put(), cleanup behavior, and measured leak rate. ## 4. Severity interpretation This behaves like an ordinary Moderate or Low-like resource exhaustion issue rather than an Important-class kernel vulnerability. The practical impact is local DoS through memory leakage under repeated enqueue operations. The theoretical risk does not extend to memory corruption or privilege escalation based on the patch context, because the leaked object remains referenced rather than freed and reused unsafely. ## 5. One-sentence report phrase A local DMA fence reference leak in the IIO DMABUF enqueue path can leak one kmalloc-128 object per successful enqueue, allowing sustained local use of the device interface to cause memory exhaustion and denial of service. ## 6. Manual review recommendation NO MANUAL CHECK NEEDED This can be handled as an auto-close candidate for most environments because it is a bounded resource leak class with no supported memory corruption, LPE, network exposure, or security-boundary bypass. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: iio: buffer: Fix DMA fence leak in iio_buffer_enqueue_dmabuf() Commit: 9678aeed8b77d495a417dd057d479f3733094019 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9678aeed8b77d495a417dd057d479f3733094019 Commit description: iio_buffer_enqueue_dmabuf() allocates a struct iio_dma_fence (104 bytes, kmalloc-128) via kmalloc_obj()+dma_fence_init(), which sets the initial kref to 1. It then calls dma_resv_add_fence() which takes a second reference (kref=2), and stores a raw pointer in block->fence. On the success path the function returns without calling dma_fence_put() to release the initial reference, so every buffer enqueue permanently leaks one kmalloc-128 allocation. The iio_buffer_cleanup() work item only releases the temporary reference taken during completion signalling by iio_buffer_signal_dmabuf_done(); the initial reference from dma_fence_init() is never released. With four iio_rwdev instances at 240kHz and 512 samples per buffer, this produces ~1875 kmalloc-128 allocations per second matching the observed slab growth exactly. A test with ftrace confirmed that the dma_fence_destroy event was never triggered. Fix by calling dma_fence_put() after dma_resv_add_fence(), transferring ownership of the fence to the DMA reservation object. The DMA fence then gets properly discarded after being signalled. Fixes: 3e26d9f ("iio: core: Add new DMABUF interface infrastructure") Originally-by: James Nuss Signed-off-by: Benoît Monin Reviewed-by: Paul Cercueil Cc: Signed-off-by: Jonathan Cameron Signed-off-by: Greg Kroah-Hartman Changed files: drivers/iio/industrialio-buffer.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=9678aeed8b77d495a417dd057d479f3733094019 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-63929 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63929 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:L/PR:L/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 5.5 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: 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: LOW KPANIC detected for this report: NO Published priority for this report (same as in Subject): LOW 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).