From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-53122][MODERATE REGULAR] btrfs: fix deadlock between reflink and transaction commit when using flushoncommit [ Upstream Date: Wed, 24 Jun 2026 16:00:11 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-53122 X-AL-KERNEL-Priority: MODERATE REGULAR X-AL-KERNEL-Severity: MODERATE REGULAR X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 4 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: 73be4a08306bb84f4d5d16f62cb80e1543109ffa List-Id: CVE: CVE-2026-53122 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: btrfs: fix deadlock between reflink and transaction commit when using flushoncommit [ Upstream Commit: 73be4a08306bb84f4d5d16f62cb80e1543109ffa Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=73be4a08306bb84f4d5d16f62cb80e1543109ffa Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53122 Analysis date: Wed, 24 Jun 2026 16:00:11 -0400 ActionableScore: 4 ActionableScore lower bound: 3 Actionable bucket: Borderline, manual review recommended Manual review required: YES Summary: A local user with write access to a Btrfs filesystem mounted with flushoncommit may trigger a reflink versus transaction commit deadlock by copying inline extent data beyond i_size, causing filesystem writeback and commit operations to hang. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53122 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53122 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: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-53122 MODERATE 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-833;CWE-362;**CWE-400;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A Btrfs deadlock can occur when a reflink operation copies inline extent data to an offset beyond the destination inode i_size while the filesystem is mounted with flushoncommit. The copied data creates a dirty folio beyond EOF, and a concurrent transaction commit can trigger delalloc writeback that tries to invalidate that folio and waits on an extent lock held by the reflink path. The reflink path then waits for the current transaction to unblock before it can update the inode item, creating a circular wait and leaving tasks stuck in D state. For the CVSS the PR:L is used because a local user with write access to files on the affected Btrfs mount can trigger reflink style operations such as copy_file_range(), while no administrative privileges are normally needed for the file operation itself. The issue is not network reachable and does not provide a direct confidentiality or integrity primitive. Impact is denial of service through a hung transaction commit and degraded or blocked filesystem operations.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 4) YES DEADLOCK DANGER DISK INIT SKIP HARDWARE SYZBOT INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=3 ## 1. ActionableScore * Conservative score: 3 * Paranoid score: 4 * Final recommended bucket: **Borderline, manual review recommended**:: ## 2. Signal breakdown Conservative signals: * Local unprivileged trigger: +1 A local user with write access to the affected Btrfs mount can trigger reflink style operations via copy_file_range(). * Reliable kernel hang / strong DoS: +1 The bug creates a circular wait between reflink, writeback, and transaction commit, leaving tasks stuck in D state. * Important filesystem/storage path: +1 The affected path is Btrfs reflink, writeback, delalloc flushing, and transaction commit. Paranoid additional signal: * Availability impact realistic: +1 The deadlock can block transaction commit and filesystem writeback, causing persistent filesystem-level availability degradation until recovery or reboot. Conservative subtraction: * Hard/specific trigger conditions: -1 The trigger requires flushoncommit, inline extents, reflink beyond current i_size, and a concurrent transaction commit. ## 3. Reachability analysis The bug is locally reachable by a user able to operate on files in a Btrfs filesystem and invoke reflink/copy_file_range style operations. It does not require network access and is not remotely triggerable. It does not normally require CAP_SYS_ADMIN for the reflink operation itself, but the vulnerable configuration depends on the filesystem being mounted with flushoncommit, which is an administrator-controlled mount option. Containers may matter only if they expose writable Btrfs-backed paths where reflink operations reach the host filesystem. ## 4. Severity interpretation This behaves like a borderline actionable Moderate rather than an Important vulnerability. The patch and commit describe a deadlock and hung tasks, not UAF, OOB write, page-cache corruption, credential bypass, or another concrete memory corruption primitive. The realistic impact is denial of service against Btrfs transaction/writeback progress. Theoretical privilege escalation is not supported by the patch context. ## 5. One-sentence report phrase A local user with write access to a Btrfs filesystem mounted with flushoncommit may trigger a reflink versus transaction commit deadlock by copying inline extent data beyond i_size, causing filesystem writeback and commit operations to hang. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED Reason: this is not memory corruption and does not justify Important-class handling by itself, but it affects Btrfs transaction/writeback availability and has syzbot-reported hung tasks, so it should not be blindly auto-closed without confirming deployment exposure to flushoncommit and untrusted local reflink operations. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: btrfs: fix deadlock between reflink and transaction commit when using flushoncommit [ Upstream Commit: 73be4a08306bb84f4d5d16f62cb80e1543109ffa Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=73be4a08306bb84f4d5d16f62cb80e1543109ffa Changed files: kernel/sched/core.c fs/btrfs/extent-io-tree.c fs/btrfs/extent-io-tree.h fs/btrfs/inode.c fs/btrfs/extent_io.c mm/page-writeback.c fs/fs-writeback.c kernel/workqueue.c kernel/kthread.c arch/x86/kernel/process.c arch/x86/entry/entry_64.S fs/btrfs/transaction.c fs/btrfs/reflink.c fs/read_write.c arch/x86/entry/syscall_64.c fs/btrfs/ioctl.c fs/ioctl.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=73be4a08306bb84f4d5d16f62cb80e1543109ffa ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-53122 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53122 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: 3 Paranoid ActionableScore: 4 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 alexanjelausa@gmail.com (and both send reply to CVE record itself too and see "reply" button below for howto reply).