From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-89515][MODERATE REGULAR] scsi: core: Fill in DMA padding bytes in scsi_alloc_sgtables() Date: Fri, 11 Sep 2026 21:42:41 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-89515 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: a4353ec7742bdf87dcdde5875270feb3a1982a51 List-Id: CVE: CVE-2026-89515 Priority: MODERATE REGULAR AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: scsi: core: Fill in DMA padding bytes in scsi_alloc_sgtables() Commit: a4353ec7742bdf87dcdde5875270feb3a1982a51 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a4353ec7742bdf87dcdde5875270feb3a1982a51 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89515 Analysis date: Fri, 11 Sep 2026 21:42:41 -0400 ActionableScore: 4 ActionableScore lower bound: 3 Actionable bucket: Borderline / manual review recommended Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89515 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89515 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-2026-89515 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-89515 CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N';CWE-908;*CWE-200;CWE-665;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N';BEST CVSS score: '5.5';DESCR 'Uninitialized DMA padding bytes can be included in the last SCSI scatterlist entry when scsi_alloc_sgtables extends last_sg.length for dma_pad_mask alignment. A local process can trigger this path through SG_IO or a related SCSI block device ioctl with a request size that needs padding, causing uninitialized kernel memory bytes to be mapped for DMA. For the CVSS the PR:L is used because reliable triggering requires local access to an affected SCSI device interface, but full administrative privileges are not always required on systems that delegate SG_IO access. The issue is not network reachable. Impact is primarily confidentiality exposure to a SCSI device, controller, or virtual device backend, with no direct evidence of integrity impact, privilege escalation, or denial of service.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4) YES READ KASAN DMAorINTERRUPT HARDWARE TEST MEMORY DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=4 ActionableScoreLower=3 PrimitiveClass=NONE RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=NO ImportantCandidate=NO ManualReview=RECOMMENDED AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 3 * Conservative score: 3. No floor or cap applied. * Raw paranoid score: 4 * Paranoid score: 4. No floor or cap applied. * Final recommended bucket: **Borderline / manual review recommended**:: 2. Signal breakdown Conservative signals: * +1 Confidentiality plausible. Uninitialized DMA padding bytes may be exposed to a SCSI device, controller, or virtual backend. * +1 Memory layout invariant restoration. The patch restores consistency between scatterlist length extension and initialized bytes by zeroing the added padding. * +1 Important storage path. The bug is in SCSI core request scatterlist handling and is reachable through SG_IO style block device paths. * +0 Local unprivileged trigger not awarded conservatively. Local SG_IO or block device ioctl access is shown, but ordinary unprivileged reachability for all deployments is not established. * +0 Reliable crash or DoS not awarded. The evidence is KMSAN uninitialized value use, not a kernel panic or host-wide availability failure. * +0 Integrity not awarded. No write primitive, corruption of protected state, or privilege escalation path is shown. * +0 UAF or lifetime corruption not awarded. No freed object, stale reference, double release, or refcount mutation is involved. * +0 Remote reachability not awarded. The trigger is local device ioctl or block layer request processing, not network traffic. Paranoid additional signal: * +1 Local below-host-admin exposure considered. Systems may delegate access to SG_IO or removable SCSI block devices to non-root users or services, making a practical below-host-admin trigger plausible. Important non-awarded signals: * Controlled reclaim not demonstrated. * Arbitrary write not demonstrated. * Real UAF not demonstrated. * Concrete repeated release or refcount mutation not present. * Substantial kernel disclosure not proven. The directly described leak is limited padding bytes, although repetition may increase sensitivity. * AutoDowngradeAllowed remains YES because no Class A or Class B corruption, boundary bypass, COW violation, or unresolved lifetime primitive is established. 3. Reachability analysis The visible path is local: SG_IO, scsi_ioctl, sr_block_ioctl, blkdev_ioctl, request mapping, SCSI queueing, and DMA mapping. A local process that can issue SG_IO or related ioctls to an affected SCSI block device can shape a request size that requires DMA padding. Full host administrator privilege is not positively required in all deployments because device-node permissions or service delegation may allow below-host-admin access. However, ordinary unprivileged reachability is deployment dependent. No namespace-scoped privilege model is involved. No network trigger is established. No special race is required. The issue depends on a SCSI or ATA-backed path with a dma_pad_mask alignment requirement and on a device or backend that can observe or receive the padded DMA bytes. Physical hardware is not strictly required because a virtual SCSI backend could also be relevant. 4. Primitive and severity interpretation The primitive is uninitialized kernel memory exposure through DMA padding bytes. It is not memory corruption, not UAF, not an OOB write, and not a repeated lifetime/refcount mutation. The affected storage is a scatterlist entry whose length is extended for DMA alignment before the padding bytes are initialized. Demonstrated consequence is KMSAN reporting uninitialized bytes passed into DMA mapping. Practical security consequence is possible disclosure of small kernel memory fragments to the DMA endpoint. The more serious paranoid interpretation is that repeated triggering or a controlled virtual/device backend may make the disclosure more meaningful, but the patch does not establish arbitrary read, write, LPE, or host crash. PrimitiveClass is NONE because no corruption, lifetime, ownership, or authorization primitive is established. ImportantCandidate is NO because the issue is a limited information disclosure candidate rather than an Important-grade corruption or boundary-bypass primitive. AutoDowngradeAllowed is YES because the current evidence supports borderline/manual-review handling, not forced Important preservation. 5. One-sentence report phrase Uninitialized DMA padding bytes in scsi_alloc_sgtables can be mapped to a SCSI device or virtual backend through SG_IO style local requests, potentially exposing small amounts of kernel memory without evidence of integrity impact, privilege escalation, or remote reachability. 6. Manual review recommendation MANUAL CHECK RECOMMENDED Reason: the issue is likely limited to confidentiality exposure through DMA padding, but environment-specific SG_IO permissions and whether the DMA endpoint is attacker-observable should be checked before auto-closing. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: scsi: core: Fill in DMA padding bytes in scsi_alloc_sgtables() Commit: a4353ec7742bdf87dcdde5875270feb3a1982a51 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a4353ec7742bdf87dcdde5875270feb3a1982a51 Commit description: During fuzz testing, the following issue was discovered: BUG: KMSAN: uninit-value in __dma_map_sg_attrs+0x217/0x310 __dma_map_sg_attrs+0x217/0x310 dma_map_sg_attrs+0x4a/0x70 ata_qc_issue+0x9f8/0x1420 __ata_scsi_queuecmd+0x1657/0x1740 ata_scsi_queuecmd+0x79a/0x920 scsi_queue_rq+0x4472/0x4f40 blk_mq_dispatch_rq_list+0x1cca/0x3ee0 __blk_mq_sched_dispatch_requests+0x458/0x630 blk_mq_sched_dispatch_requests+0x15b/0x340 __blk_mq_run_hw_queue+0xe5/0x250 __blk_mq_delay_run_hw_queue+0x138/0x780 blk_mq_run_hw_queue+0x4bb/0x7e0 blk_mq_sched_insert_request+0x2a7/0x4c0 blk_execute_rq+0x497/0x8a0 sg_io+0xbe0/0xe20 scsi_ioctl+0x2b36/0x3c60 sr_block_ioctl+0x319/0x440 blkdev_ioctl+0x80f/0xd70 __se_sys_ioctl+0x219/0x420 __x64_sys_ioctl+0x93/0xe0 x64_sys_call+0x1d6c/0x3ad0 do_syscall_64+0x4c/0xa0 entry_SYSCALL_64_after_hwframe+0x6e/0xd8 Uninit was created at: __alloc_pages+0x5c0/0xc80 alloc_pages+0xe0e/0x1050 blk_rq_map_user_iov+0x2b77/0x6100 blk_rq_map_user_io+0x2fa/0x4d0 sg_io+0xad6/0xe20 scsi_ioctl+0x2b36/0x3c60 sr_block_ioctl+0x319/0x440 blkdev_ioctl+0x80f/0xd70 __se_sys_ioctl+0x219/0x420 __x64_sys_ioctl+0x93/0xe0 x64_sys_call+0x1d6c/0x3ad0 do_syscall_64+0x4c/0xa0 entry_SYSCALL_64_after_hwframe+0x6e/0xd8 Bytes 14-15 of 16 are uninitialized Memory access of size 16 starts at ffff88800cbdb000 When processing the last unaligned element of the scatterlist, it is supplemented with missing bytes in the amount of pad_len. These bytes remain uninitialized, which leads to a problem. Extend last_sg->length by pad_len first, then use sg_zero_buffer() to zero those pad_len bytes. sg_zero_buffer() uses sg_miter internally, which correctly handles sg entries spanning multiple pages and padding that crosses a page boundary. Found by Linux Verification Center (linuxtesting.org) with Syzkaller. Fixes: 40b01b9 ("block: update bio according to DMA alignment padding") Cc: stable@vger.kernel.org Signed-off-by: Petr Vaganov Reviewed-by: Bart Van Assche Link: https://patch.msgid.link/20260628185229.37957-1-p.vaganov@ideco.ru Signed-off-by: Martin K. Petersen (Oracle) Signed-off-by: Greg Kroah-Hartman Changed files: drivers/scsi/scsi_lib.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=a4353ec7742bdf87dcdde5875270feb3a1982a51 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-89515 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89515 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:L/PR:L/UI:N/S:U/C:L/I:N/A:N The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N 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).