From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-97937][MODERATE 7.0] ftrace: fork: Initialize function graph state before copy_exec_state() Date: Fri, 25 Sep 2026 14:28:44 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-97937 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: 4 X-AL-KERNEL-Commit: 1fadebbbf31f65beba353fa9d1373bf183e03fed List-Id: CVE: CVE-2026-97937 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: ftrace: fork: Initialize function graph state before copy_exec_state() Commit: 1fadebbbf31f65beba353fa9d1373bf183e03fed Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1fadebbbf31f65beba353fa9d1373bf183e03fed Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97937 Analysis date: Fri, 25 Sep 2026 14:28:44 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-97937 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97937 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 7.0 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-2026-97937 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-97937 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:H/I:H/A:H';*CWE-416;CWE-665;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A use-after-free occurs because dup_task_struct copies the parent function graph ret_stack pointer into the child before the child tracing state is initialized. If copy_exec_state fails during a non-CLONE_VM fork, the child cleanup path frees the copied ret_stack even though it still belongs to the parent. The parent can then perform an 8 byte write to the freed slab object from function_graph_enter_regs, which can cause kernel memory corruption and a system crash. For the CVSS the PR:L value is used because a local process is required to reach the fork path, while administrator privileges may only be needed to enable function graph tracing beforehand. AC:H is used because triggering depends on a specific allocation failure after dup_task_struct and before tracing state initialization. The issue is not network reachable. Impact is at least a local denial of service via kernel crash and in the worst case may allow confidentiality or integrity impact due to memory corruption and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) SKIP CVE-2026-97937 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE DANGER INIT ERRORPATH UAF HARDWARE LINUS KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=4 PrimitiveClass=CLASS_B RealUAF=YES HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=NO ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO 1. ActionableScore * Raw conservative score: 4 * Conservative score: 4 * Raw paranoid score: 5 * Paranoid score: 5 * No floor or cap changed either score. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown Conservative signals: * +2 Real UAF. The failed child cleanup frees the parent active `ret_stack`, after which the parent accesses the allocation. * +1 Reliable kernel crash or strong DoS. KASAN confirms a slab UAF, and the non-instrumented consequence can include kernel corruption or a fatal fault. * +1 Weak exploitation concern. `function_graph_enter_regs()` performs a concrete 8-byte post-free write, making this stronger than a read-only stale dereference. The target and replacement contents are not shown to be controlled. * 0 negative points. The sequence is an ordered allocation-failure path, not a timing race. No unsupported privilege or rarity penalty is applied. Paranoid-only signal: * +1 Attacker-influenced repeatable lifetime sequence. Once function graph tracing is active, repeated non-`CLONE_VM` forks under allocation pressure can repeatedly drive child creation, failed initialization, erroneous release, and subsequent parent use. This increases reclaim opportunity but does not establish controlled reclaim. Important non-awarded signals: * Controlled reclaim, attacker-selected replacement objects, and arbitrary or directed writes are not demonstrated. * Strong LPE leverage is not awarded. * Structured stale-object leverage is not separately awarded because no attacker-shaped replacement state or security-relevant field consumption is established. * Local unprivileged trigger is not awarded because the supplied evidence does not establish the complete below-host-admin chain, including tracing setup and reliable allocation failure. * Remote reachability, confidentiality disclosure, and a demonstrated privilege escalation are not established. * No extra Availability point is awarded because it would duplicate the same UAF crash consequence. * This is not a repeated-release/refcount case. The first operation frees the aliased `ret_stack`, but the later operation is a post-free data write rather than a second `put`, release, free, or refcount mutation. * Concrete repeated release/refcount +1 was not awarded. * Paranoid repeated-refcount leverage +1 was not awarded. * REAL UAF FLOOR 5 was not applied. The paranoid score reaches 5 through arithmetic, not through a floor. 3. Reachability analysis Function graph tracing must be active so that the parent owns a live `ret_stack`. Enabling or configuring this tracer normally involves host-controlled tracefs access, but the supplied evidence does not prove whether the attacker must perform that setup or may attack a system where it is already active. Therefore, `HostAdminRequired=UNKNOWN`. After tracing is enabled, the vulnerable operation is reached through an ordinary non-`CLONE_VM` fork. Triggering additionally requires `copy_exec_state()` allocation failure. A process may influence this through repeated forks and memory pressure, but reliable ordinary-user triggering is not directly demonstrated. No race is required because the vulnerable sequence is ordered through the error path. The tracing configuration is host-global rather than an attacker-created namespace capability. No namespace-scoped complete trigger exists in the supplied evidence. There is no network vector, special hardware requirement, or device dependency. 4. Primitive and severity interpretation The exact primitive is an active-object slab UAF with a concrete post-free write. `dup_task_struct()` copies the parent `ret_stack` pointer into the child. Before the child state is cleared, `copy_exec_state()` can fail, causing child cleanup to free the allocation still owned and actively used by the parent. The parent later writes eight bytes through the dangling pointer. This is broader than an ordinary cleanup-only stale dereference because the erroneous free happens during child cleanup, while the subsequent stale use occurs in the surviving parent during normal function graph tracing. It is not a concrete repeated-release case because the second operation writes tracing state rather than performing another lifetime or refcount mutation. The primitive is CLASS_B rather than CLASS_A. Kernel memory corruption is established, but controlled reclaim, attacker-directed destination or payload, callback control, arbitrary read or write, and privilege escalation are not. The demonstrated consequence is UAF memory corruption with realistic kernel crash or DoS. A stronger consequence is technically plausible if the freed slab allocation is reused before the parent write, but useful replacement control is unresolved. `ImportantCandidate=YES` because an active surviving task performs a confirmed write into freed slab memory, leaving meaningful exploitation leverage unresolved. `AutoDowngradeAllowed=NO` because automatically treating this as an ordinary crash-only issue would discard the concrete post-free write primitive. Operationally, it is at least Actionable Moderate and requires Important-vs-Moderate review. 5. One-sentence report phrase A failed non-CLONE_VM fork can free the parent function graph return stack and leave the surviving parent performing an 8-byte write into freed slab memory, creating a local kernel UAF with crash impact and unresolved exploitation potential. 6. Manual review recommendation MANUAL CHECK REQUIRED The confirmed post-free slab write is stronger than an immediate stale-pointer fault, but reclaim control, attacker privilege, and practical escalation potential require manual validation. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: ftrace: fork: Initialize function graph state before copy_exec_state() Commit: 1fadebbbf31f65beba353fa9d1373bf183e03fed Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1fadebbbf31f65beba353fa9d1373bf183e03fed Commit description: dup_task_struct() copies the parent's task_struct, including ret_stack. ftrace_graph_init_task() clears the copied function graph state, but it currently runs after copy_exec_state(). For non-CLONE_VM forks, copy_exec_state() allocates a new task_exec_state. If that allocation fails, copy_process() reaches bad_fork_free and free_task() calls ftrace_graph_exit_task(). Since the child still carries the parent's ret_stack pointer, the unwind frees the parent's active function graph return stack. The parent subsequently accesses freed memory from function_graph_enter_regs(). KASAN reports: [ 22.190920] ================================================================== [ 22.195899] BUG: KASAN: slab-use-after-free in function_graph_enter_regs+0xa76/0xb90 [ 22.200747] Write of size 8 at addr ff110000054dc0a8 by task repro/1 [ 22.205134] [ 22.210770] CPU: 0 UID: 0 PID: 1 Comm: repro Not tainted 7.2.0-07732-g9328b3b03bdc-dirty #3 PREEMPT(lazy) [ 22.212576] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 [ 22.213750] Call Trace: [ 22.215271] [ 22.216242] ? ftrace_stub_direct_tramp+0x10/0x10 [ 22.217774] dump_stack_lvl+0x4e/0x70 [ 22.220531] print_report+0x157/0x4b4 [ 22.223202] ? fixup_red_left+0x9/0x30 [ 22.224407] ? complete_report_info+0x83/0x110 [ 22.226679] ? function_graph_enter_regs+0xa76/0xb90 [ 22.228084] kasan_report+0xce/0x100 [ 22.230109] ? function_graph_enter_regs+0xa76/0xb90 [ 22.232860] ? stack_trace_save+0x4/0xd0 [ 22.234156] function_graph_enter_regs+0xa76/0xb90 [ 22.236090] ? kasan_save_stack+0x30/0x50 [ 22.237752] ? __pfx_function_graph_enter_regs+0x10/0x10 [ 22.238694] ? ring_buffer_lock_reserve+0x345/0xf80 [ 22.239628] ? stack_trace_save+0x4/0xd0 [ 22.242121] ? stack_trace_save+0x4/0xd0 [ 22.243588] ftrace_graph_func+0xda/0x160 [ 22.245362] ? ftrace_stub_direct_tramp+0x10/0x10 [ 22.246520] 0xffffffffa0000095 [ 22.250528] ? stack_trace_save+0x9/0xd0 [ 22.251757] ? ring_buffer_unlock_commit+0x11d/0x5c0 [ 22.253152] stack_trace_save+0x9/0xd0 [ 22.254264] kasan_save_stack+0x30/0x50 [ 22.273631] kasan_save_track+0x14/0x30 [ 22.276763] kasan_save_free_info+0x3b/0x70 [ 22.278296] __kasan_slab_free+0x43/0x70 [ 22.280157] kmem_cache_free+0xbf/0x3b0 [ 22.282963] ? ftrace_stub_direct_tramp+0x10/0x10 [ 22.284001] free_task+0xa2/0x160 [ 22.285699] ? ftrace_stub_direct_tramp+0x10/0x10 [ 22.286752] copy_process+0x2aae/0x7bc0 Initialize the child function graph state immediately after dup_task_struct(), before the first fallible operation. Cc: stable@vger.kernel.org Fixes: 6b1c66c ("exec_state: relocate dumpable information") Reviewed-by: Bradley Morgan Link: https://patch.msgid.link/20260822195321.962383-2-Jeremy.Jean@oss.cyber.gouv.fr Assisted-by: Codex:gpt-5 Signed-off-by: Jérémy Jean Signed-off-by: Steven Rostedt Signed-off-by: Greg Kroah-Hartman Changed files: kernel/fork.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=1fadebbbf31f65beba353fa9d1373bf183e03fed ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-97937 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97937 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:L/I:L/A:H The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 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: 4 Paranoid ActionableScore: 5 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: YES Published priority for this report (same as in Subject): MODERATE 7.0 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).