From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-46040][LOW] inotify: fix watch count leak when fsnotify_add_inode_mark_locked() fails Date: Wed, 27 May 2026 10:19:03 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-46040 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: 8bcc1cd237ab5ccfdd102869fa031c541943cf40 List-Id: CVE: CVE-2026-46040 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: inotify: fix watch count leak when fsnotify_add_inode_mark_locked() fails Commit: 8bcc1cd237ab5ccfdd102869fa031c541943cf40 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8bcc1cd237ab5ccfdd102869fa031c541943cf40 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46040 Analysis date: Wed, 27 May 2026 10:19:03 -0400 ActionableScore: 2 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate / Low-like Manual review required: NO Summary: A local inotify error path can leak the per-namespace watch count when mark insertion fails, allowing repeated failures to exhaust `max_user_watches` and cause inotify DoS without memory corruption or privilege escalation. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46040 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46040 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-2026-46040 LOW CHECK 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-772;**CWE-400;CWE-770;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A resource accounting leak can occur in inotify_new_watch() when inc_inotify_watches() succeeds but fsnotify_add_inode_mark_locked() later fails. The error path removes the temporary mark from the idr but does not decrement the per namespace watch counter, so repeated failures can exhaust max_user_watches and make future inotify_add_watch() calls fail with ENOSPC even when no watches are active. For the CVSS the PR:L is used because a local user can normally invoke inotify watch creation, but reliable triggering requires making the mark insertion fail repeatedly. 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 against inotify watch quota only.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) YES DISK SIMPLEFIX LEAK ERRORPATH LINUS NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 ## 1. ActionableScore * Conservative score: 2 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate / Low-like**:: ## 2. Signal breakdown Triggered signals: * Local unprivileged trigger: +1 `inotify_add_watch()` is normally reachable by local unprivileged users. * Broad/default/common subsystem exposure: +1 inotify/fsnotify is a common Linux userspace API. * Availability impact realistic: +1 Repeated failures can leak the per-namespace watch count and exhaust `max_user_watches`, causing later watch creation to fail with `ENOSPC`. Subtracting signals: * Hard or unreliable trigger condition: -1 The attacker must repeatedly cause `fsnotify_add_inode_mark_locked()` to fail after `inc_inotify_watches()` succeeds, which is not the normal successful watch-add path. No signals apply for memory corruption, UAF, OOB access, arbitrary write, privilege escalation, sensitive-object access, remote reachability, or security-boundary bypass. ## 3. Reachability analysis A local user can reach the inotify watch creation path, but reliable exploitation requires repeatedly hitting the specific error path where mark insertion fails after the watch counter has already been incremented. Namespaces matter because the affected accounting is per namespace after the per-namespace limits conversion, but the bug does not appear to bypass namespace isolation. It mainly consumes the affected user or namespace watch quota. The path is not network reachable. It is default-available on normal Linux systems, but the practical DoS is limited to inotify watch quota exhaustion rather than system-wide compromise. ## 4. Severity interpretation This behaves like an ordinary Moderate or Low-like local resource accounting bug. It can cause denial of service for inotify users by exhausting `max_user_watches`, but it does not create a real object lifetime corruption primitive. Theoretical impact is quota exhaustion. Realistic evidence does not support memory corruption, information disclosure, integrity impact, or privilege escalation. ## 5. One-sentence report phrase A local inotify error path can leak the per-namespace watch count when mark insertion fails, allowing repeated failures to exhaust `max_user_watches` and cause inotify DoS without memory corruption or privilege escalation. ## 6. Manual review recommendation NO MANUAL CHECK NEEDED This is a local resource accounting leak with constrained DoS impact only and no supported memory corruption, remote exposure, or privilege-escalation primitive. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: inotify: fix watch count leak when fsnotify_add_inode_mark_locked() fails Commit: 8bcc1cd237ab5ccfdd102869fa031c541943cf40 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8bcc1cd237ab5ccfdd102869fa031c541943cf40 Commit description: When fsnotify_add_inode_mark_locked() fails in inotify_new_watch(), the error path calls inotify_remove_from_idr() but does not call dec_inotify_watches() to undo the preceding inc_inotify_watches(). This leaks a watch count, and repeated failures can exhaust the max_user_watches limit with -ENOSPC even when no watches are active. Prior to commit 1cce1ee ("inotify: Convert to using per-namespace limits"), the watch count was incremented after fsnotify_add_mark_locked() succeeded, so this path was not affected. The conversion moved inc_inotify_watches() before the mark insertion without adding the corresponding rollback. Add the missing dec_inotify_watches() call in the error path. Fixes: 1cce1ee ("inotify: Convert to using per-namespace limits") Cc: stable@vger.kernel.org Signed-off-by: Chia-Ming Chang Signed-off-by: robbieko Reviewed-by: Nikolay Borisov Link: https://patch.msgid.link/20260224093442.3076294-1-chiamingc@synology.com Signed-off-by: Jan Kara Signed-off-by: Greg Kroah-Hartman Changed files: fs/notify/inotify/inotify_user.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=8bcc1cd237ab5ccfdd102869fa031c541943cf40 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-46040 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46040 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:L 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).