From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-80841][IMPORTANT] net/packet: defer vmalloc TX_RING free until skbs finish Date: Fri, 04 Sep 2026 13:15:24 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-80841 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 7 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: 0189dce07db2dc059ae0570e06758ec4233c6e11 List-Id: CVE: CVE-2026-80841 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: net/packet: defer vmalloc TX_RING free until skbs finish Commit: 0189dce07db2dc059ae0570e06758ec4233c6e11 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0189dce07db2dc059ae0570e06758ec4233c6e11 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80841 Analysis date: Fri, 04 Sep 2026 13:15:24 -0400 ActionableScore: 7 ActionableScore lower bound: 5 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: AF_PACKET TX_RING can free vmalloc backed ring storage while outstanding TX skbs still hold raw frame pointers, allowing a local CAP_NET_RAW capable process to trigger a stale kernel write during skb destruction with at least DoS impact and plausible memory corruption risk. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80841 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80841 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: IMPORTANT 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-2026-80841 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-80841 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-362;*CWE-787;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'AF_PACKET TX_RING skbs keep raw pointers to mmap ring frames. For vmalloc backed ring blocks, page references do not preserve the vmalloc mapping, so socket close or ring replacement can free the mapping while outstanding TX skbs still later write timestamp and TP_STATUS_AVAILABLE to the frame. This is a local race and lifetime bug with a use-after-free style write in skb destruction context. For the CVSS the PR:L value is used because triggering requires local code able to create and use AF_PACKET TX_RING, typically CAP_NET_RAW in a network namespace or an equivalent delegated capability. The issue is not directly network reachable because packet traffic alone does not create or replace the vulnerable ring. Impact is at least local denial of service via kernel crash and in the paranoid case may include confidentiality and integrity impact due to kernel memory corruption, so manual review is needed.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) YES REMOTE READ INIT SKB PACKET KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=7 ActionableScoreLower=5 ## 1. ActionableScore * Conservative score: 5 * Paranoid score: 7 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative scoring: * +1 Local low privilege or namespace mediated trigger. AF_PACKET TX_RING is reachable from local code with CAP_NET_RAW, and in some deployments this may be obtainable in user or network namespaces. * +2 Generic memory corruption. The patch describes outstanding TX skbs keeping raw pointers to mmap ring frames after vmalloc backed ring memory can be freed. * +1 Real lifetime corruption. This is a lifetime mismatch between skb completion/destructor access and TX_RING/pg_vec teardown. * +1 Reliable kernel crash / strong DoS. A late skb destructor can write timestamp and TP_STATUS_AVAILABLE through a stale ring frame pointer. * +1 Weak LPE concern. The bug is a writable stale pointer into freed vmalloc backed memory, but no attacker controlled reclaim or reliable object replacement is demonstrated. * +1 Broad/default/common subsystem exposure. AF_PACKET is a common Linux networking facility, even if TX_RING usage is specialized. * -1 Hard or unreliable race / special timing required. The issue depends on outstanding TX skbs racing with close or ring replacement. * -1 Corruption primitive constrained. The late write contents are mainly timestamp/status data, not an arbitrary attacker chosen payload. Paranoid delta: * +1 additional LPE plausibility, upgrading weak concern to stronger concern because the primitive is write after lifetime end in kernel context. * +1 local high-control kernel data-plane API refinement, only for deployments where AF_PACKET TX_RING is practically reachable by less trusted users through namespaces or delegated CAP_NET_RAW. ## 3. Reachability analysis The bug is local, not directly network reachable. Packet traffic alone does not create, replace, or close the vulnerable TX_RING. A trigger requires local code that can create an AF_PACKET socket, configure TX_RING, send frames, and race socket close or ring replacement against skb completion. In typical hardened deployments this requires CAP_NET_RAW, so it is not plain remote unauthenticated exposure. In containerized or namespace-enabled environments, CAP_NET_RAW may be delegated to less trusted workloads, which makes PR:L and manual review more appropriate. The path is not a rare hardware-only path and does not require a special NIC firmware condition. Call-site confidence: high. The provided patch includes the relevant destructor, release path, ring allocation, ring replacement, and deferred free logic. ## 4. Severity interpretation This is stronger than an ordinary Moderate DoS because the patch fixes a real lifetime bug where kernel code can write through a stale raw pointer after vmalloc backed ring memory is detached or freed. The realistic demonstrated impact is local kernel crash or DoS. The theoretical higher impact is local privilege escalation through vmalloc reuse or related memory corruption, but the patch does not demonstrate a reliable reclaim or arbitrary write primitive. Therefore the conservative result is Actionable Moderate. The paranoid result is a Strong Important candidate because AF_PACKET is a historically security sensitive local networking API and the bug class is writable UAF style lifetime corruption. ## 5. One-sentence report phrase AF_PACKET TX_RING can free vmalloc backed ring storage while outstanding TX skbs still hold raw frame pointers, allowing a local CAP_NET_RAW capable process to trigger a stale kernel write during skb destruction with at least DoS impact and plausible memory corruption risk. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: this is not a pure resource leak or validation bug. The patch context supports a real lifetime corruption issue with stale writable ring frame pointers in AF_PACKET TX_RING, making it unsuitable for auto-close even though reliable privilege escalation is not demonstrated. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net/packet: defer vmalloc TX_RING free until skbs finish Commit: 0189dce07db2dc059ae0570e06758ec4233c6e11 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0189dce07db2dc059ae0570e06758ec4233c6e11 Commit description: AF_PACKET TX_RING skbs keep a raw pointer to their ring frame. The skb page references preserve page-backed ring blocks after pg_vec is freed, but they do not preserve a vmalloc mapping. tpacket_destruct_skb() currently drops the pending reference before writing the timestamp and TP_STATUS_AVAILABLE to the frame. Move the decrement after those stores. The smp_wmb() in __packet_set_status() orders the frame stores before the decrement. Also recheck pending TX frames under pg_vec_lock before non-closing ring replacement, so a racing send cannot add a pending skb between the initial check and the ring swap. Ring allocation can produce a mixture of page-backed and vmalloc-backed blocks. Allocate deferred-work storage during TX ring setup when the first vmalloc-backed block is encountered, and keep its pointer in the pg_vec allocation header. If allocation fails, return -ENOMEM from ring setup. On socket close, a non-NULL pointer identifies a vmalloc-backed vector without a scan. If TX skbs remain, defer the whole vector to system_long_wq. After pg_vec is detached, a late destructor can skip the pending decrement. Use socket write-memory accounting as the deferred lifetime gate instead: an skb remains charged through its final sock_wfree(), after all ring-frame accesses. The delayed work retains a socket reference and reschedules itself until no TX skbs remain. Move pending_refcnt release to packet_sock_destruct() so late skb destructors and deferred cleanup can safely use it after packet_release(). Page-backed teardown remains synchronous, and no lock is added to the TX completion hot path. Fixes: b013840 ("packet: use percpu mmap tx frame pending refcount") Cc: stable@vger.kernel.org Link: https://lore.kernel.org/netdev/20260721015824.45829-1-kylebot@openai.com/ Suggested-by: Eric Dumazet Suggested-by: Willem de Bruijn Reviewed-by: Willem de Bruijn Signed-off-by: Kyle Zeng Link: https://patch.msgid.link/20260816235646.76500-1-kylebot@openai.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman Changed files: net/packet/af_packet.c net/inet_common.h 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=0189dce07db2dc059ae0570e06758ec4233c6e11 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-80841 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80841 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: 5 Paranoid ActionableScore: 7 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: IMPORTANT KPANIC detected for this report: YES Published priority for this report (same as in Subject): IMPORTANT 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).