From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-46050][MODERATE REGULAR] md/raid10: fix deadlock with check operation and nowait requests Date: Wed, 27 May 2026 11:35:30 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-46050 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: 3 X-AL-KERNEL-ActionableScore-Lower: 2 X-AL-KERNEL-Commit: 965d6162dd88cc7cc193cf7f5bfc132d8bbf0523 List-Id: CVE: CVE-2026-46050 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: md/raid10: fix deadlock with check operation and nowait requests Commit: 965d6162dd88cc7cc193cf7f5bfc132d8bbf0523 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=965d6162dd88cc7cc193cf7f5bfc132d8bbf0523 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46050 Analysis date: Wed, 27 May 2026 11:35:30 -0400 ActionableScore: 3 ActionableScore lower bound: 2 Actionable bucket: Borderline, manual review recommended Manual review required: YES Summary: NOWAIT IO during an active md RAID10 check can underflow `nr_pending`, leaving resync and normal IO stuck behind the barrier and causing local storage DoS. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46050 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46050 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-2026-46050 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-191;**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 'A local denial of service can occur in md raid10 when NOWAIT IO races with an active array check. NOWAIT requests do not increment nr_pending in wait_barrier(), but the old failure path called raid_end_bio_io(), which can call allow_barrier() and decrement nr_pending anyway. This can underflow nr_pending and leave the md resync thread waiting forever for nr_pending to become 0, while other IO waits in the barrier path. For the CVSS the PR:L is used because a local user may be able to issue NOWAIT IO against an existing RAID10 backed filesystem, although reliable triggering also requires an active check or resync state. The issue is not network reachable and does not involve UAF, out of bounds access, arbitrary write, information disclosure, or privilege escalation. Impact is denial of service only through RAID10 IO deadlock and system responsiveness loss.';NO MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3) YES OOB DEADLOCK DISK LEAK IMPROVEONLY KERNEL_PANIC_PLUS_UAF LINUS INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=3 ActionableScoreLower=2 ## 1. ActionableScore * Conservative score: 2 * Paranoid score: 3 * Final recommended bucket: **Borderline, manual review recommended**:: ## 2. Signal breakdown Conservative signals: * Local unprivileged trigger: +1 A local user may be able to issue NOWAIT IO against a filesystem backed by an existing RAID10 array. * Important filesystem/storage path: +1 md RAID10 is a core storage subsystem, and a deadlock can affect all IO on the array. * Reliable DoS: +1 The commit describes a reproducible deadlock where `nr_pending` underflows and the md resync thread waits indefinitely. * Availability impact realistic: +1 The result can be system-wide storage IO stall for the affected array. Subtracting signals: * Special state required: -1 Requires an active array check/resync barrier. * Configuration dependent: -1 Requires md RAID10 and workloads using NOWAIT IO. Paranoid adjustment: * Shared storage impact concern: +1 On multi-user hosts or storage appliances, a local workload can affect broader IO availability for unrelated users and services. No signals apply for memory corruption, UAF, OOB access, arbitrary write, information disclosure, privilege escalation, or remote reachability. ## 3. Reachability analysis The issue is local. A user can potentially generate NOWAIT IO, but the bug requires the RAID10 array to be in a check/resync state where barriers are raised. Starting the check may require admin privileges, but checks can also be scheduled or already running. Namespaces and containers matter if untrusted workloads share storage backed by the affected RAID10 array. The issue is not network reachable by itself, though remote services using the storage may be affected indirectly by the IO deadlock. ## 4. Severity interpretation This behaves like a local storage DoS, not an Important memory corruption issue. The bug is an accounting mismatch around `nr_pending`, not UAF or write corruption. Realistic impact is RAID10 IO deadlock and system responsiveness loss. Theoretical escalation beyond DoS is not supported by the patch. ## 5. One-sentence report phrase NOWAIT IO during an active md RAID10 check can underflow `nr_pending`, leaving resync and normal IO stuck behind the barrier and causing local storage DoS. ## 6. Manual review recommendation MANUAL CHECK RECOMMENDED Reason: no memory corruption or privilege escalation is shown, but the bug affects shared storage availability and can deadlock IO on an affected RAID10 array. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: md/raid10: fix deadlock with check operation and nowait requests Commit: 965d6162dd88cc7cc193cf7f5bfc132d8bbf0523 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=965d6162dd88cc7cc193cf7f5bfc132d8bbf0523 Commit description: When an array check is running it will raise the barrier at which point normal requests will become blocked and increment the nr_pending value to signal there is work pending inside of wait_barrier(). NOWAIT requests do not block and so will return immediately with an error, and additionally do not increment nr_pending in wait_barrier(). Upstream change commit 43806c3 ("raid10: cleanup memleak at raid10_make_request") added a call to raid_end_bio_io() to fix a memory leak when NOWAIT requests hit this condition. raid_end_bio_io() eventually calls allow_barrier() and it will unconditionally do an atomic_dec_and_test(&conf->nr_pending) even though the corresponding increment on nr_pending didn't happen in the NOWAIT case. This can be easily seen by starting a check operation while an application is doing nowait IO on the same array. This results in a deadlocked state due to nr_pending value underflowing and so the md resync thread gets stuck waiting for nr_pending to == 0. Output of r10conf state of the array when we hit this condition: crash> struct r10conf barrier = 1, nr_pending = { counter = -41 }, nr_waiting = 15, nr_queued = 0, Example of md_sync thread stuck waiting on raise_barrier() and other requests stuck in wait_barrier(): md1_resync [<0>] raise_barrier+0xce/0x1c0 [<0>] raid10_sync_request+0x1ca/0x1ed0 [<0>] md_do_sync+0x779/0x1110 [<0>] md_thread+0x90/0x160 [<0>] kthread+0xbe/0xf0 [<0>] ret_from_fork+0x34/0x50 [<0>] ret_from_fork_asm+0x1a/0x30 kworker/u1040:2+flush-253:4 [<0>] wait_barrier+0x1de/0x220 [<0>] regular_request_wait+0x30/0x180 [<0>] raid10_make_request+0x261/0x1000 [<0>] md_handle_request+0x13b/0x230 [<0>] __submit_bio+0x107/0x1f0 [<0>] submit_bio_noacct_nocheck+0x16f/0x390 [<0>] ext4_io_submit+0x24/0x40 [<0>] ext4_do_writepages+0x254/0xc80 [<0>] ext4_writepages+0x84/0x120 [<0>] do_writepages+0x7a/0x260 [<0>] __writeback_single_inode+0x3d/0x300 [<0>] writeback_sb_inodes+0x1dd/0x470 [<0>] __writeback_inodes_wb+0x4c/0xe0 [<0>] wb_writeback+0x18b/0x2d0 [<0>] wb_workfn+0x2a1/0x400 [<0>] process_one_work+0x149/0x330 [<0>] worker_thread+0x2d2/0x410 [<0>] kthread+0xbe/0xf0 [<0>] ret_from_fork+0x34/0x50 [<0>] ret_from_fork_asm+0x1a/0x30 Fixes: 43806c3 ("raid10: cleanup memleak at raid10_make_request") Cc: stable@vger.kernel.org Signed-off-by: Josh Hunt Link: https://lore.kernel.org/linux-raid/20260303005619.1352958-1-johunt@akamai.com Signed-off-by: Yu Kuai Signed-off-by: Greg Kroah-Hartman Changed files: drivers/md/raid10.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=965d6162dd88cc7cc193cf7f5bfc132d8bbf0523 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46050 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46050 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: 2 Paranoid ActionableScore: 3 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).