From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-64465][LOW] usb: xhci: Fix sleep in atomic context in xhci_free_streams() Date: Sat, 25 Jul 2026 11:56:12 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-64465 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: 1 X-AL-KERNEL-ActionableScore-Lower: 0 X-AL-KERNEL-Commit: e623e4a203f56d5c57519a9a3cb29600551534ad List-Id: CVE: CVE-2026-64465 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: usb: xhci: Fix sleep in atomic context in xhci_free_streams() Commit: e623e4a203f56d5c57519a9a3cb29600551534ad Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e623e4a203f56d5c57519a9a3cb29600551534ad Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64465 Analysis date: Sat, 25 Jul 2026 11:56:12 -0400 ActionableScore: 1 ActionableScore lower bound: 0 Actionable bucket: Ordinary Moderate / Low-like physical DoS Manual review required: NO Summary: A USB xHCI disconnect path can call dma_free_coherent() while holding a spinlock with IRQs disabled, allowing a physical USB device scenario with active stream endpoints to trigger a kernel BUG or crash. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64465 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64465 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-2026-64465 LOW CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-667;CWE-703;*CWE-664;Other CVSS 'AV:P/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.6';DESCR 'xhci_free_streams() can call dma_free_coherent() while holding xhci lock with IRQs disabled when a USB device with active stream endpoints is disconnected. dma_free_coherent() may sleep for large stream context arrays, which is invalid in atomic context and can trigger a BUG or kernel crash. For the CVSS the PR:N because the physical trigger does not require an OS account on the victim, but the vector is physical rather than network reachable. Impact is denial of service only. There is no evidence of a UAF, OOB access, information leak, or privilege escalation primitive in this patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like physical DoS (with actual score 1) YES USB INIT HARDWARE MEMORY DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=1 ActionableScoreLower=0 ## 1. ActionableScore * Conservative score: 0 * Paranoid score: 1 * Final recommended bucket: **Ordinary Moderate / Low-like physical DoS** ## 2. Signal breakdown Triggered signals: * Reliable kernel crash / strong DoS: +1 The commit describes a BUG caused by calling dma_free_coherent() from atomic context while xhci->lock is held with IRQs disabled. * Broad/default/common subsystem: +1 xHCI/USB host support is common on Linux systems, although the vulnerable condition requires USB stream endpoints. Subtracted signals: * Physical-only or rare hardware-only condition: -2 The realistic trigger is disconnecting a USB device with active stream endpoints. This is not network reachable and requires physical or equivalent device-level access. Paranoid-only signal: * Availability impact realistic: +1 In the worst practical interpretation, a prepared USB3/UASP-style device with active streams could cause a host-visible kernel BUG or crash on disconnect. This is still DoS only. Not awarded: * No remote reachable signal. * No local unprivileged trigger signal in the normal syscall sense. * No generic memory corruption signal. * No UAF, OOB write, double free, refcount takeover, type confusion, arbitrary write, or privilege escalation signal. * No confidentiality or integrity impact. ## 3. Reachability analysis The bug is triggered during USB disconnect handling when xhci_free_streams() frees stream resources for endpoints using streams. The attacker model is physical or device-adjacent, such as a user plugging or unplugging a capable USB device, or a malicious USB peripheral. No OS account is required for the physical trigger, but the attack is not remotely reachable over the network. Namespaces and containers do not materially lower the trigger requirement because the relevant event is host USB device removal handled by the host kernel. The path is common in the sense that xHCI is broadly deployed, but the specific stream endpoint condition is narrower than ordinary USB device handling. ## 4. Severity interpretation This behaves like a Low-like or ordinary Moderate denial-of-service issue, not an Important-class vulnerability. The failure mode is sleep-in-atomic leading to BUG or kernel crash. The patch moves the potentially sleeping free operation outside the spinlock, which supports a locking/context correctness issue rather than a memory corruption primitive. Theoretical impact is limited to availability. Realistic exploitation evidence does not support privilege escalation, data corruption, information disclosure, or attacker-controlled memory corruption. ## 5. One-sentence report phrase A USB xHCI disconnect path can call dma_free_coherent() while holding a spinlock with IRQs disabled, allowing a physical USB device scenario with active stream endpoints to trigger a kernel BUG or crash. ## 6. Manual review recommendation NO MANUAL CHECK NEEDED This is a physical DoS-only issue with a clear locking-context root cause and no evidence of memory corruption, privilege escalation, confidentiality impact, or network reachability. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: usb: xhci: Fix sleep in atomic context in xhci_free_streams() Commit: e623e4a203f56d5c57519a9a3cb29600551534ad Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e623e4a203f56d5c57519a9a3cb29600551534ad Commit description: When a USB device with active stream endpoints is disconnected, xhci_free_streams() is called from the hub_event workqueue to free the stream resources. It calls xhci_free_stream_info() while holding xhci->lock with irqs disabled. xhci_free_stream_info() invokes xhci_free_stream_ctx(), which calls dma_free_coherent() for large stream context arrays. dma_free_coherent() can sleep (e.g. via vunmap), triggering a BUG when called from atomic context. Call trace: dma_free_attrs+0x174/0x220 xhci_free_stream_info+0xd0/0x11c xhci_free_streams+0x278/0x37c usb_free_streams+0x98/0xc0 usb_unbind_interface+0x1b8/0x2f8 device_release_driver_internal+0x1d4/0x2cc device_release_driver+0x18/0x28 bus_remove_device+0x160/0x1a4 device_del+0x1ec/0x350 usb_disable_device+0x98/0x214 usb_disconnect+0xf0/0x35c hub_event+0xab4/0x19ec process_one_work+0x278/0x63c Fix this by saving the stream_info pointers and clearing the ep references under the lock, then calling xhci_free_stream_info() outside the lock where sleeping is allowed. Fixes: 8df75f4 ("USB: xhci: Add memory allocation for USB3 bulk streams.") Cc: stable Signed-off-by: Lianqin Hu Signed-off-by: Mathias Nyman Link: https://patch.msgid.link/20260703144033.483286-3-mathias.nyman@linux.intel.com Signed-off-by: Greg Kroah-Hartman Changed files: drivers/usb/host/xhci.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=e623e4a203f56d5c57519a9a3cb29600551534ad ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64465 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64465 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:P/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 4.6 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: 0 Paranoid ActionableScore: 1 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).