From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-64102][IMPORTANT] RDMA/siw: Reject MPA FPDU length underflow before signed receive math Date: Sun, 19 Jul 2026 23:34:52 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-64102 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: 8 X-AL-KERNEL-ActionableScore-Lower: 7 X-AL-KERNEL-Commit: 683f7cfbf514193d63c0efa079f3352bde84c2e0 List-Id: CVE: CVE-2026-64102 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: RDMA/siw: Reject MPA FPDU length underflow before signed receive math Commit: 683f7cfbf514193d63c0efa079f3352bde84c2e0 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=683f7cfbf514193d63c0efa079f3352bde84c2e0 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64102 Analysis date: Sun, 19 Jul 2026 23:34:52 -0400 ActionableScore: 8 ActionableScore lower bound: 7 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A malicious connected Soft iWARP peer can send a malformed MPA FPDU with an underflowed length that reaches `skb_copy_bits()` as a huge copy size, causing KASAN-confirmed UAF/OOB read behavior and at least a remote DoS with plausible confidentiality or integrity concerns. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64102 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64102 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-2026-64102 IMPORTANT CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H';CWE-191;CWE-195;*CWE-416;CWE-125;Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';Other CVSS 'AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H';BEST CVSS score: '9.8';DESCR 'A peer controlled MPA FPDU length in RDMA siw can be smaller than the fixed DDP/RDMAP header length for the selected opcode. This causes an integer underflow in fpdu_part_rem and the resulting negative signed length can flow through memory checks and into skb_copy_bits as a huge copy length. KASAN reports a use after free read in skb_copy_bits with a multi gigabyte read size, so the issue should be treated as a memory corruption candidate rather than a simple protocol warning. For the CVSS the PR:N value is used because a malicious connected siw peer can send the malformed FPDU without needing a local account or privileges on the victim system. The issue is network reachable within environments where Soft iWARP RDMA endpoints are exposed, typically storage or data center networks rather than the public Internet. Impact is at least remote denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to the UAF/OOB copy primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8) YES READ OOB DANGER INIT UAF NETWORK SKB KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=8 ActionableScoreLower=7 ## 1. ActionableScore * Conservative score: 7 * Paranoid score: 8 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Remote reachable / network-triggerable: +2. A malicious connected Soft iWARP peer can send the malformed FPDU over the SIW TCP receive path. * Generic memory corruption, strong primitive: +2. The patch context shows peer-controlled integer underflow reaching `skb_copy_bits()` as a huge copy length, with KASAN reporting use-after-free read. * Real lifetime corruption: +1. KASAN reports UAF in `skb_copy_bits()`, not merely a warning or validation failure. * Reliable kernel crash / strong DoS: +1. The described path can cause a kernel crash through a malformed FPDU. * Confidentiality impact plausible: +1. A huge copy from stale or out-of-bounds skb memory may expose kernel or stale memory contents depending on destination visibility. * Rare AND difficult-to-reach subsystem/configuration: -1. SIW/RDMA endpoints are usually deployed in storage or data-center fabrics and are not normally Internet-exposed. Paranoid delta: * Integrity impact plausible: +1. The negative length also bypasses memory range validation before a huge copy into the receive target, so a limited integrity concern is defensible even if not proven as arbitrary kernel write. ## 3. Reachability analysis The bug is triggerable by a connected SIW/iWARP peer that can send a malformed FPDU with an MPA length smaller than the opcode header requirement. No local account or victim-side privileges are required once the SIW endpoint is reachable. This is network-triggerable in RDMA-over-TCP deployments, but practical exposure is usually limited to storage, HPC, or data-center networks rather than the public Internet. Namespaces and containers are not the main factor here. The key precondition is that Soft iWARP is enabled and accepting connections from an untrusted or compromised peer. Call-site confidence: high. The commit message provides the downstream flow from `siw_get_hdr()` through `siw_tcp_rx_data()`, `siw_check_mem()`, `siw_rx_data()`, and `skb_copy_bits()`, plus a KASAN trace from the real TCP receive path. ## 4. Severity interpretation This behaves more like an Important-class kernel memory-corruption candidate than an ordinary Moderate DoS. The realistic demonstrated impact is remote or network-adjacent kernel crash. The theoretical higher impact is supported by a concrete primitive: peer-controlled length underflow, signed-to-unsigned copy length expansion, failed memory bounds validation, and KASAN UAF read. There is no demonstrated arbitrary write or exploit chain, so the conservative score stays below Critical-class handling, but the issue should not be auto-closed as a routine RDMA protocol validation bug. ## 5. One-sentence report phrase A malicious connected Soft iWARP peer can send a malformed MPA FPDU with an underflowed length that reaches `skb_copy_bits()` as a huge copy size, causing KASAN-confirmed UAF/OOB read behavior and at least a remote DoS with plausible confidentiality or integrity concerns. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: this is network-triggerable in SIW deployments and the patch context shows a concrete memory-corruption path, not just input validation or a warning. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: RDMA/siw: Reject MPA FPDU length underflow before signed receive math Commit: 683f7cfbf514193d63c0efa079f3352bde84c2e0 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=683f7cfbf514193d63c0efa079f3352bde84c2e0 Commit description: A malicious connected siw peer can send an iWARP FPDU whose MPA length field (c_hdr->mpa_len, 16 bit big-endian, peer-controlled) is smaller than the fixed DDP/RDMAP header for the announced opcode. Soft-iWARP parses the full header in siw_get_hdr() based on iwarp_pktinfo[opcode] .hdr_len, but never compares mpa_len against that header length. siw_tcp_rx_data() then derives srx->fpdu_part_rem = be16_to_cpu(mpa_len) - fpdu_part_rcvd + MPA_HDR_SIZE; where fpdu_part_rcvd equals iwarp_pktinfo[opcode].hdr_len at this point. For a tagged WRITE (hdr_len 16, MPA_HDR_SIZE 2) the smallest on-wire mpa_len of 0 yields fpdu_part_rem = -14, and any mpa_len below hdr_len - MPA_HDR_SIZE underflows to a negative int. The signed value then flows into siw_proc_write()/siw_proc_rresp() as bytes = min(srx->fpdu_part_rem, srx->skb_new); is handed to siw_check_mem() as an int len (whose interval check addr + len > mem->va + mem->len is satisfied for a valid base when len is negative), and reaches siw_rx_data() -> siw_rx_kva() / siw_rx_umem() -> skb_copy_bits() as a signed copy length. The header copy branch in skb_copy_bits() promotes that to size_t, producing a multi-gigabyte read. KASAN under a KUnit harness that drives the real kernel TCP receive path -- a loopback AF_INET socketpair, the malformed FPDU written via kernel_sendmsg, sk_data_ready firing in softirq, tcp_read_sock dispatching to siw_tcp_rx_data -- reports: BUG: KASAN: use-after-free in skb_copy_bits+0x284/0x480 Read of size 4294967295 at addr ffff888 ... Call Trace: skb_copy_bits siw_rx_kva siw_rx_data siw_check_mem siw_proc_write siw_tcp_rx_data __tcp_read_sock siw_qp_llp_data_ready tcp_data_ready tcp_data_queue Add the missing invariant at the earliest point where the peer header is fully assembled. iwarp_pktinfo[*].hdr_len - MPA_HDR_SIZE is exactly the value the siw transmitter uses as the minimum mpa_len for each opcode (drivers/infiniband/sw/siw/siw_qp.c:33), so this matches the protocol contract. Out-of-range FPDUs terminate the connection with TERM_ERROR_LAYER_LLP / LLP_ETYPE_MPA / LLP_ECODE_FPDU_START -- which is RFC 5044 Section 8 error code 3 ("Marker and ULPDU Length fields do not agree on the start of an FPDU"), the correct framing-error class for this inconsistency. Fixes: 8b6a361 ("rdma/siw: receive path") Link: https://patch.msgid.link/r/20260513175325.2042630-2-michael.bommarito@gmail.com Cc: stable@vger.kernel.org Signed-off-by: Michael Bommarito Assisted-by: Claude:claude-opus-4-7 Acked-by: Bernard Metzler Signed-off-by: Jason Gunthorpe Signed-off-by: Greg Kroah-Hartman Changed files: drivers/infiniband/sw/siw/siw_qp.c drivers/infiniband/sw/siw/siw_qp_rx.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=683f7cfbf514193d63c0efa079f3352bde84c2e0 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64102 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64102 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:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 9.8 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: 7 Paranoid ActionableScore: 8 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).