From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-52949][LOW] drm/ttm: Fix ttm_bo_shrink() infinite LRU walk on backup failure Date: Fri, 26 Jun 2026 15:29:18 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-52949 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: 9402ad98a047dd9894ec868a7df5ad9bd03327d3 List-Id: CVE: CVE-2026-52949 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: drm/ttm: Fix ttm_bo_shrink() infinite LRU walk on backup failure Commit: 9402ad98a047dd9894ec868a7df5ad9bd03327d3 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9402ad98a047dd9894ec868a7df5ad9bd03327d3 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52949 Analysis date: Fri, 26 Jun 2026 15:29:18 -0400 ActionableScore: 2 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate / Low-like Manual review required: NO Summary: `ttm_bo_shrink()` may repeatedly walk the same TTM LRU entries after backup failure, allowing a local GPU user to cause a reclaim stall or CPU hang, with impact limited to denial of service. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-52949 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52949 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-2026-52949 LOW CHECK 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-835;CWE-834;**CWE-400;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'ttm_bo_shrink() can enter an infinite LRU walk when backup of a TTM buffer object fails after the object was removed from bulk move handling too early. A local user with access to DRM render or GPU allocation interfaces may be able to trigger this by creating GPU buffer pressure and forcing shrinker activity where ttm_tt_backup() returns an error or cannot make progress. For the CVSS the PR:L is used for the paranoid score because practical triggering can be done by a local unprivileged or low privileged GPU user on systems that expose render nodes, not by a remote network attacker. The issue is not network reachable and does not show a UAF, OOB access, or arbitrary write primitive. Impact is denial of service through CPU hang or reclaim stall only.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) MAYBE LOCK SIMPLEFIX HARDWARE INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 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 * Local unprivileged trigger: +1 A local user with access to DRM render or GPU allocation interfaces may be able to create TTM buffer objects and memory pressure. * Reliable kernel crash / strong DoS: +1 The bug can cause an infinite LRU walk or reclaim stall in `ttm_bo_shrink()` after backup failure. * Broad/default/common subsystem: +1 DRM TTM is used by common GPU drivers on systems with exposed render nodes. * Hard or unreliable condition required: -1 Triggering depends on shrinker activity plus `ttm_tt_backup()` failure or lack of progress, so this is not a simple deterministic syscall crash. No points for memory corruption, UAF, OOB access, page-cache corruption, confidentiality impact, integrity impact, or network reachability. ## 3. Reachability analysis The issue is locally reachable on systems where unprivileged users can access DRM render nodes or otherwise create GPU buffer pressure. It is not network reachable. Namespaces or containers may matter if GPU devices are passed through or render nodes are exposed to container workloads, but this does not change the bug class. The affected path is configuration dependent because it requires a TTM based DRM driver and a backup failure or reclaim pressure condition. ## 4. Severity interpretation This behaves like an ordinary Moderate local DoS issue, not an Important class vulnerability. The patch and commit message support an infinite LRU walk and availability impact, but do not show memory corruption, stale pointer use, attacker controlled overwrite, object confusion, or a plausible privilege escalation path. Theoretical impact beyond DoS is not supported by the patch context. ## 5. One-sentence report phrase `ttm_bo_shrink()` may repeatedly walk the same TTM LRU entries after backup failure, allowing a local GPU user to cause a reclaim stall or CPU hang, with impact limited to denial of service. ## 6. Manual review recommendation NO MANUAL CHECK NEEDED Reason: this is a local DoS-only LRU progress bug with no demonstrated memory corruption or privilege escalation primitive. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: drm/ttm: Fix ttm_bo_shrink() infinite LRU walk on backup failure Commit: 9402ad98a047dd9894ec868a7df5ad9bd03327d3 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9402ad98a047dd9894ec868a7df5ad9bd03327d3 Commit description: Apply the same fix as b2ed01e ("drm/ttm: Fix ttm_bo_swapout() infinite LRU walk on swapout failure") to the ttm_bo_shrink() path. Move del_bulk_move from before the backup to after success only, using ttm_resource_del_bulk_move_unevictable() since the resource is now unevictable once fully backed up. Fixes: 70d645d ("drm/ttm: Add helpers for shrinking") Cc: Christian König Cc: Huang Rui Cc: Matthew Auld Cc: Matthew Brost Cc: Dave Airlie Cc: dri-devel@lists.freedesktop.org Cc: stable@vger.kernel.org # v6.15+ Assisted-by: GitHub_Copilot:claude-opus-4.6 Reviewed-by: Matthew Auld Link: https://patch.msgid.link/20260511162443.24352-1-thomas.hellstrom@linux.intel.com Signed-off-by: Thomas Hellström Signed-off-by: Greg Kroah-Hartman Changed files: drivers/gpu/drm/ttm/ttm_bo_util.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=9402ad98a047dd9894ec868a7df5ad9bd03327d3 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-52949 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52949 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: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).