From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-43494][IMPORTANT] net/rds: reset op_nents when zerocopy page pin fails When iov_iter_get_pages2() fails in rds_message_zcopy_from_user(), the pinned pages are released with put_page(), and rm->data.op_mmp_znotifier is cleared. But we fail to properly clear rm->data.op_nents. Later when rds_message_purge() is called from rds_sendmsg() the cleanup loop iterates over the incorrectly non zero number of op_nents and frees them again. Fix this by properly resetting op_nents when it should be in rds_message_zcopy_from_user(). Fixes: 0cebacc ("rds: zerocopy Tx support.") Signed-off-by: Allison Henderson Reviewed-by: Simon Horman Link: https://patch.msgid.link/20260505234336.2132721-1-achender@kernel.org Signed-off-by: Jakub Kicinski Date: Thu, 21 May 2026 10:52:15 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-43494 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: e174929793195e0cd6a4adb0cad731b39f9019b4 List-Id: CVE: CVE-2026-43494 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: net/rds: reset op_nents when zerocopy page pin fails When iov_iter_get_pages2() fails in rds_message_zcopy_from_user(), the pinned pages are released with put_page(), and rm->data.op_mmp_znotifier is cleared. But we fail to properly clear rm->data.op_nents. Later when rds_message_purge() is called from rds_sendmsg() the cleanup loop iterates over the incorrectly non zero number of op_nents and frees them again. Fix this by properly resetting op_nents when it should be in rds_message_zcopy_from_user(). Fixes: 0cebacc ("rds: zerocopy Tx support.") Signed-off-by: Allison Henderson Reviewed-by: Simon Horman Link: https://patch.msgid.link/20260505234336.2132721-1-achender@kernel.org Signed-off-by: Jakub Kicinski Commit: e174929793195e0cd6a4adb0cad731b39f9019b4 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e174929793195e0cd6a4adb0cad731b39f9019b4 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43494 Analysis date: Thu, 21 May 2026 10:52:15 -0400 ActionableScore: 8 ActionableScore lower bound: 7 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A local RDS zerocopy send error path can release pinned pages twice after `iov_iter_get_pages2()` failure because `op_nents` is not reset, creating page refcount lifetime corruption with DoS and plausible privilege escalation risk. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-43494 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43494 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-2026-43494 IMPORTANT CHECK Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-415;*CWE-416;CWE-911;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'A local memory lifetime bug exists in the RDS zero copy send path when iov_iter_get_pages2() fails after pages were pinned. The error path releases the pinned pages but leaves rm data op_nents non zero, so later rds_message_purge() can release the same pages again. For the CVSS the PR:L is used because a local user or process may be able to reach the RDS sendmsg zero copy path when AF_RDS and the relevant configuration are available. The issue is not directly network reachable because the trigger is a local sendmsg operation rather than received packet processing. Impact is at least local denial of service and the page reference lifetime corruption creates a plausible use after free or privilege escalation concern that should not be autoclosed.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8) SKIP CVE-2026-43494 SKIP No affected files built, so skip this CVE NO - - unknown MAYBE SIMPLEFIX IMPROVEONLY KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7 - - 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 * Local unprivileged trigger: +1 A local process may trigger the RDS `sendmsg()` zerocopy path if AF_RDS and zerocopy support are available. * Local unprivileged high-control kernel data-plane API: +1 The attacker can shape user iovecs and failure conditions around `iov_iter_get_pages2()` in a kernel networking transmit path. * Generic memory corruption, strong corruption primitive: +2 The bug causes the same pinned pages to be released twice via repeated `put_page()`, which is a page refcount lifetime corruption pattern. * Real lifetime corruption: +1 This is a real reference lifetime bug: pages are unpinned, but `op_nents` remains non zero, causing later cleanup to operate on stale accounting. * Reliable kernel crash / strong DoS: +1 Double page release can plausibly cause refcount underflow, page lifetime corruption, kernel warnings, crashes, or memory-management instability. * Privilege escalation plausible: +1 conservative / +2 paranoid Conservative view treats this as a weak to moderate LPE concern because page refcount corruption can become exploitable but no concrete reclaim primitive is shown. Paranoid view gives stronger weight because double `put_page()` on user-controlled pinned pages is historically a dangerous primitive. * Confidentiality and integrity impact plausible: +1 paranoid combined interpretation If the page lifetime corruption becomes controllable, reused pages could theoretically affect data confidentiality or integrity. This is not proven by the patch, but it is defensible for manual-review sensitivity. * Rare/configuration dependency: -1 conservative only RDS is not universally enabled or exposed on all systems, and triggering depends on AF_RDS plus zerocopy Tx availability. This does not eliminate risk where the module/interface is available. ## 3. Reachability analysis The trigger is local, not remote packet processing. A local user or process can potentially reach it through AF_RDS `sendmsg()` with zerocopy if RDS support is enabled and accessible. Containers or namespaces may matter if AF_RDS sockets are available inside the namespace, but many deployments restrict or do not load RDS. Realistic exploitation requires inducing a partial page-pin failure after some pages were pinned, then reaching the later purge path. That is more plausible than a narrow timing race because it is an error-path cleanup bug, not a pure race. ## 4. Severity interpretation This should be treated as a Strong Important candidate rather than ordinary Moderate. The realistic demonstrated impact is at least local DoS from double page release and page refcount corruption. The theoretical but credible higher impact is privilege escalation through page lifetime misuse after premature page release. The patch does not prove arbitrary write or a full exploit chain, so it is not Critical by itself, but double `put_page()` on user-influenced pinned pages is serious enough to avoid auto-closure. ## 5. One-sentence report phrase A local RDS zerocopy send error path can release pinned pages twice after `iov_iter_get_pages2()` failure because `op_nents` is not reset, creating page refcount lifetime corruption with DoS and plausible privilege escalation risk. ## 6. Manual review recommendation MANUAL CHECK REQUIRED. This is a local page lifetime corruption and double-release bug in a networking zerocopy path. Even without a demonstrated exploit, the primitive is strong enough to require manual review. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: net/rds: reset op_nents when zerocopy page pin fails When iov_iter_get_pages2() fails in rds_message_zcopy_from_user(), the pinned pages are released with put_page(), and rm->data.op_mmp_znotifier is cleared. But we fail to properly clear rm->data.op_nents. Later when rds_message_purge() is called from rds_sendmsg() the cleanup loop iterates over the incorrectly non zero number of op_nents and frees them again. Fix this by properly resetting op_nents when it should be in rds_message_zcopy_from_user(). Fixes: 0cebacc ("rds: zerocopy Tx support.") Signed-off-by: Allison Henderson Reviewed-by: Simon Horman Link: https://patch.msgid.link/20260505234336.2132721-1-achender@kernel.org Signed-off-by: Jakub Kicinski Commit: e174929793195e0cd6a4adb0cad731b39f9019b4 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e174929793195e0cd6a4adb0cad731b39f9019b4 Changed files: net/rds/message.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=e174929793195e0cd6a4adb0cad731b39f9019b4 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-43494 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-43494 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:L/PR:L/UI:N/S:U/C:L/I:L/A:H The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 7.8 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).