From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-97549][LOW] xfs: fix under-reservation of blocks when repairing sf directories Date: Fri, 25 Sep 2026 11:55:27 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-97549 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: b950e84acd072ac648ace4fea53c0b1212da4b2c List-Id: CVE: CVE-2026-97549 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: xfs: fix under-reservation of blocks when repairing sf directories Commit: b950e84acd072ac648ace4fea53c0b1212da4b2c Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b950e84acd072ac648ace4fea53c0b1212da4b2c Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97549 Analysis date: Fri, 25 Sep 2026 11:55:27 -0400 ActionableScore: 2 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-97549 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97549 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-2026-97549 LOW https://www.kernelcve.org/list/?q=CVE-2026-97549 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-400;CWE-682;CWE-703;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'An XFS metadata repair operation can under reserve transaction blocks when converting a shortform directory or xattr structure on filesystems where a directory or attribute block spans multiple filesystem blocks. A local actor who can invoke the XFS scrub repair path on a specially configured XFS filesystem may trigger an assertion or filesystem shutdown, causing denial of service. For the CVSS the paranoid score uses PR:L because a service account, container root, or delegated storage management context may be able to invoke the repair workflow without full host administration. The issue is not network reachable and requires a specific filesystem geometry and repair scenario. Impact is limited to availability through filesystem shutdown. No memory corruption, information disclosure, or privilege escalation primitive is indicated by the patch. NO MANUAL CHECK REQUIRED COULD BE AUTOCLOSED.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) YES DANGER DISK HARDWARE LINUS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 PrimitiveClass=NONE RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 2 * Conservative score: 2 * Raw paranoid score: 2 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +1 Reliable filesystem shutdown or strong DoS. The commit explicitly states that insufficient transaction reservation can cause an XFS filesystem shutdown. * +1 Important filesystem and storage path. The flaw affects XFS metadata repair and transaction reservation for directory or xattr structure conversion. Not awarded: * No UAF, double free, stale pointer, refcount misuse, OOB access, arbitrary write, or controlled corruption is established. * No filesystem ownership or COW violation is established. The patch corrects reservation accounting and does not show cross file modification or unauthorized data access. * No confidentiality or integrity signal is awarded. A filesystem shutdown does not itself establish metadata corruption, disclosure, or unauthorized modification. * No local unprivileged trigger is awarded. The supplied context shows xfs_scrub running as UID 0 but does not fully expose the capability checks for the repair ioctl. * No host administrator penalty is applied. Host admin equivalence is likely for normal host filesystem repair workflows, but the complete authorization path is not visible in the supplied context. * No special geometry penalty is applied. A multi filesystem block directory geometry is required, but the evidence does not establish that an attacker cannot reach such a filesystem. * No race penalty applies. This is an accounting and reservation logic defect, not a timing race. 3. Reachability analysis The vulnerable path is reached through the XFS metadata scrub and repair ioctl path, specifically while repairing shortform directories or xattr structures and preparing an atomic extent exchange. The supplied trace shows the operation being performed by xfs_scrub as UID 0. A triggering filesystem requires XFS and a geometry where a directory or attribute block spans multiple filesystem blocks. Examples from the commit include a 4 KiB filesystem block with an 8 KiB directory block, or a 1 KiB filesystem block with a 4 KiB directory block. The evidence does not establish that an ordinary unprivileged user can invoke the complete repair operation against a host XFS filesystem. It also does not establish that all required mount, repair, and metadata management operations are usable solely with attacker controlled namespace scoped privileges. Therefore HostAdminRequired and NamespaceScopedPrivilege remain UNKNOWN. There is no network trigger, hardware prerequisite, or race requirement. 4. Primitive and severity interpretation The exact defect is an under reservation of XFS transaction blocks. The old code assumes that conversion of a shortform directory or xattr requires one filesystem block, although the corresponding directory or attribute structure can require multiple filesystem blocks. This is a resource accounting and filesystem transaction reservation defect. It is not a memory lifetime defect. There is no active structured stale object, no fixed stale storage, no cleanup UAF, and no second lifetime or refcount mutation. The demonstrated consequence is an assertion warning and a possible XFS filesystem shutdown when the repair transaction lacks sufficient reserved blocks. The patch does not establish metadata overwrite, corrupted ownership, cross file modification, information disclosure, privilege escalation, or a security boundary bypass. PrimitiveClass is NONE because no meaningful corruption, lifetime, authorization, ownership, or similar security primitive is established. ImportantCandidate is NO because the patch supported impact is filesystem availability only. AutoDowngradeAllowed is YES because no unresolved corruption or boundary primitive would be discarded by ordinary automated handling. Operationally, this is a configuration dependent local filesystem availability issue. It should be patched as a correctness and reliability fix, but the supplied evidence does not support Important class security treatment. 5. One-sentence report phrase An XFS metadata repair operation can under reserve transaction blocks for multi filesystem block directory or xattr structures, potentially causing an assertion or filesystem shutdown during repair. 6. Manual review recommendation NO MANUAL CHECK NEEDED The patch establishes a transaction reservation accounting bug with filesystem shutdown impact only and does not establish a memory corruption, ownership violation, authorization bypass, or privilege escalation primitive. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: xfs: fix under-reservation of blocks when repairing sf directories Commit: b950e84acd072ac648ace4fea53c0b1212da4b2c Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b950e84acd072ac648ace4fea53c0b1212da4b2c Commit description: Whilst running QA on XFS for-next as of 7.3-rc2 with MKFS_OPTIONS="-n size=8192", I observed the following (trimmed) dmesg splat: XFS: Assertion failed: args->total >= dp->i_nblocks - nblks, file: fs/xfs/libxfs/xfs_da_btree.c, line: 2387 WARNING: fs/xfs/xfs_message.c:104 at assfail+0x46/0x4a [xfs], CPU#0: xfs_scrub/1426511 CPU: 0 UID: 0 PID: 1426511 Comm: xfs_scrub Tainted: G W 7.3.0-rc2-djwx #rc2 PREEMPT(lazy) 6e418570b606a39783b0e7e7b30dc407b965f9e8 Tainted: [W]=WARN RIP: 0010:assfail+0x46/0x4a [xfs] RSP: 0018:ffffc900010d7890 EFLAGS: 00010246 RAX: 0000000000000000 RBX: 0000000000000000 RCX: 00000000ffffffd1 RDX: 0000000000000000 RSI: 0000000000000021 RDI: ffffffffa059fd38 RBP: 0000000000000002 R08: 0000000000000000 R09: 0000000000000000 R10: 000000000000000a R11: 000000007fffffff R12: ffffc900010d7940 R13: ffff888368d8f980 R14: ffffc900010d7a48 R15: ffffc900010d78d0 FS: 00007f445c5ce680(0000) GS:ffff8884a97ea000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f443803b9a8 CR3: 0000000107a4b000 CR4: 00000000003506f0 Call Trace: xfs_da_grow_inode_int+0x2e0/0x300 [xfs 5de2257e14108c136f11317e6bbb8ac77efd392c] xfs_dir2_grow_inode+0x6e/0x150 [xfs 5de2257e14108c136f11317e6bbb8ac77efd392c] xfs_dir2_sf_to_block+0x149/0x870 [xfs 5de2257e14108c136f11317e6bbb8ac77efd392c] xrep_dir_swap_prep+0xe2/0x110 [xfs 5de2257e14108c136f11317e6bbb8ac77efd392c] xrep_dir_swap+0xfb/0x2f0 [xfs 5de2257e14108c136f11317e6bbb8ac77efd392c] xrep_dir_rebuild_tree+0x99/0x100 [xfs 5de2257e14108c136f11317e6bbb8ac77efd392c] xrep_directory+0x83/0x1c0 [xfs 5de2257e14108c136f11317e6bbb8ac77efd392c] xrep_attempt+0x4f/0x1e0 [xfs 5de2257e14108c136f11317e6bbb8ac77efd392c] xfs_scrub_metadata+0x393/0x5b0 [xfs 5de2257e14108c136f11317e6bbb8ac77efd392c] xfs_ioc_scrubv_metadata+0x306/0x570 [xfs 5de2257e14108c136f11317e6bbb8ac77efd392c] xfs_file_ioctl+0xa4f/0x1150 [xfs 5de2257e14108c136f11317e6bbb8ac77efd392c] __x64_sys_ioctl+0x76/0xc0 do_syscall_64+0x7a/0x3b0 entry_SYSCALL_64_after_hwframe+0x4b/0x53 This is a consequence of commit 0fe77e5 , which added the following assertion to xfs_da_grow_inode_int: ASSERT(args->total >= dp->i_nblocks - nblks); Tracing this back to xrep_dir_swap_prep, I noticed that the xfs_da_args object that's passed to xfs_dir2_sf_to_block sets args->total to 1. This is incorrect because mkfs set the directory block size to 8k and the filesystem block size to 4k. In other words, args->total should be 2 here, not 1. Dave Chinner tripped over the same problem with the same branch through a different channel -- his test setup set the fs block size to 1k, in which case the directory block size is still set to 4k. Here, args->total should be 4. Changing the assignment of args->total to sc->mp->m_dir_geo->fsbcount makes the assertion go away, but that isn't a complete fix. In xrep_tempexch_estimate, we also incorrectly assume that a shortform conversion requires 1 fsblock when it should be m_dir_geo->fsbcount. Without that, we can under-reserve space in the transaction and cause a filesystem shutdown. Note that the xfs_dabuf_nfsb helper will compute the correct value for directories and xattr, so we use that instead of open-coding the logic. Also fix xrep_xattr_swap_prep to assign args->total via xfs_dabuf_nfsb to avoid one logic bomb if we ever support multi-fsblock attrs. Cc: stable@vger.kernel.org # v6.10 Cc: floss@jetm.me Reported-by: dgc@kernel.org Fixes: 629fdaf ("xfs: use atomic extent swapping to fix user file fork data") Tripped-by: 0fe77e5 ("xfs: assert the reservation covers each da fork growth") Signed-off-by: Darrick J. Wong Reviewed-by: Christoph Hellwig Reviewed-by: Carlos Maiolino Signed-off-by: Carlos Maiolino Signed-off-by: Greg Kroah-Hartman Changed files: fs/xfs/libxfs/xfs_da_btree.c fs/xfs/xfs_message.c fs/xfs/libxfs/xfs_da_btree.h fs/xfs/scrub/attr_repair.c fs/xfs/scrub/dir_repair.c fs/xfs/scrub/tempfile.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=b950e84acd072ac648ace4fea53c0b1212da4b2c ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-97549 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97549 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:H/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:N/I:N/A:H The Best / paranoid CVSS score: 4.7 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: 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).