From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-46215][IMPORTANT] drm: Set old handle to NULL before prime swap in change_handle Date: Wed, 01 Jul 2026 20:15:06 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-46215 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: 8 X-AL-KERNEL-ActionableScore-Lower: 6 X-AL-KERNEL-Commit: 672464dd53231509c9c771110798c56d4660e19e List-Id: CVE: CVE-2026-46215 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: drm: Set old handle to NULL before prime swap in change_handle Commit: 672464dd53231509c9c771110798c56d4660e19e Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=672464dd53231509c9c771110798c56d4660e19e Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46215 Analysis date: Wed, 01 Jul 2026 20:15:06 -0400 ActionableScore: 8 ActionableScore lower bound: 6 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A race in `drm_gem_change_handle_ioctl()` can leave a dangling GEM IDR handle after concurrent `gem_close`, allowing later dereference of freed `drm_gem_object` memory and creating a local UAF with DoS and possible LPE concern. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46215 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46215 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-2026-46215 IMPORTANT CHECK Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'drm_gem_change_handle_ioctl could temporarily expose one GEM object through two IDR handles during handle reassignment. A concurrent gem_close could drop the object and remove one handle while leaving the other handle dangling, allowing a later dereference of freed GEM object memory. For the CVSS the PR:L is used because a local user with access to a DRM device or render node can exercise GEM handle ioctls without full administrative privileges. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact because this is a kernel use-after-free race in DRM object lifetime handling.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8) MAYBE LOCK RACE ERRORPATH UAF HARDWARE KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=8 ActionableScoreLower=6 ## 1. ActionableScore * Conservative score: 6 * Paranoid score: 8 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Local unprivileged trigger: +1. A local user with access to a DRM device or render node can exercise GEM handle ioctls. * Generic memory corruption: +2. The patch describes a real use-after-free caused by a dangling GEM handle. * Real lifetime corruption: +1. One IDR handle can remain pointing to a freed `drm_gem_object`. * Reliable kernel crash / strong DoS: +1. Dereferencing the dangling handle can crash the kernel. * Broad/common subsystem: +1. DRM GEM and render-node access are common on desktop, workstation, and GPU-enabled container systems. * Hard or timing-dependent race: -1. Exploitation requires racing `change_handle` against `gem_close`. Paranoid additional signals: * Weak to strong LPE concern: +1. This is a UAF in a user-accessible kernel object lifetime path, but no controlled reclaim or write primitive is shown in the patch. * Confidentiality / integrity impact plausible: +1 combined. UAF in DRM GEM object handling can potentially move beyond DoS if freed object reuse is controllable, but this remains a manual-review hypothesis rather than demonstrated exploitation. ## 3. Reachability analysis The bug is local and reachable through DRM GEM handle management. A user with access to a render node or DRM device can potentially call the relevant ioctl and race it with `gem_close`. Containers matter if GPU devices or render nodes are passed through. In that case, a containerized workload may have enough access to trigger the bug without host root. The issue is not remotely network reachable. The path is not exotic. DRM render nodes are commonly available to unprivileged graphics or compute users, although exact access depends on device permissions and container policy. ## 4. Severity interpretation This behaves like a Strong Important candidate under paranoid triage and at least an actionable Moderate. The realistic demonstrated impact is local DoS through kernel crash. The theoretical higher impact is possible privilege escalation because the primitive is a real UAF race in a user-reachable DRM object lifetime path. No arbitrary write or concrete exploit chain is shown, so the score should not be treated as proven LPE, but it should not be auto-closed. ## 5. One-sentence report phrase A race in `drm_gem_change_handle_ioctl()` can leave a dangling GEM IDR handle after concurrent `gem_close`, allowing later dereference of freed `drm_gem_object` memory and creating a local UAF with DoS and possible LPE concern. ## 6. Manual review recommendation MANUAL CHECK REQUIRED This is a real kernel use-after-free race in a commonly exposed DRM GEM path, potentially reachable by unprivileged users with render-node access. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: drm: Set old handle to NULL before prime swap in change_handle Commit: 672464dd53231509c9c771110798c56d4660e19e Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=672464dd53231509c9c771110798c56d4660e19e Commit description: There was a potential race condition in change_handle. The ioctl briefly had a single object with two idr entries; a concurrent gem_close could delete the object and remove one of the handles while leaving the other one dangling, which could subsequently be dereferenced for a use-after-free. To fix this, do the same dance that gem_close itself does. ( f6cd7da drm: Release driver references to handle before making it available again) First idr_replace the old handle to NULL. Later, if the prime operations are successful, actually close it. create_tail required a similar dance to avoid a similar problem. ( bd46cec drm/gem: Fix race in drm_gem_handle_create_tail()) It idr_allocs the new handle with NULL, then swaps in the correct object later to avoid races. We don't need to do that here, since the only operations that could race are drm_prime, and change_handle holds the prime lock for the entire duration. v2: cleanups of error paths Signed-off-by: David Francis Co-authored-by: Dave Airlie Reported-by: Puttimet Thammasaeng Tested-by: Vitaly Prosyak Cc: Simona Vetter Cc: stable@vger.kernel.org Cc: Christian Koenig Fixes: 5309672 ("drm: Add DRM prime interface to reassign GEM handle") Signed-off-by: Dave Airlie Signed-off-by: Greg Kroah-Hartman Changed files: drivers/gpu/drm/drm_gem.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=672464dd53231509c9c771110798c56d4660e19e ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46215 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46215 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:N/A:H The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 7 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: 6 Paranoid ActionableScore: 8 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).