{"id":"CVE-2026-64525","title":"xfrm: move policy_bydst RCU sync from per-netns .exit to .pre_exit","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nxfrm: move policy_bydst RCU sync from per-netns .exit to .pre_exit\n\nThe struct pernet_operations docstring in include/net/net_namespace.h\nexplicitly warns against block…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 438b1f668ad58f46ce699bb48e4698a7839e3f9e < bca6386dc08750fc7cdcbc7683473748ba3114b9","Linux >= 3733fce2871c9bca9dd18a1a23b1432ea215a094 < 91cc13978ab0bc6f669139f53e7e613a860d10e0","Linux >= 069daad4f2ae9c5c108131995529d5f02392c446 < d14ae8ef88c2c6590e107db61b6adce148cec7b3","Linux >= 069daad4f2ae9c5c108131995529d5f02392c446 < 3e52417318473782012b236d0325bf7d2266a597","Linux b2faee12538b5b008eaef65a4201eb29cb5cefb3","Linux b66920a3348c0f63ba18365248fa21fbf0b3a937","Linux 33a3149dd81a1e2f52b80ee1e0fc380b39f3d028","Linux >= 6.12.83 < 6.12.93","Linux >= 6.18.24 < 6.18.35","Linux >= 6.1.191 < 6.2","Linux >= 6.6.136 < 6.7","Linux >= 6.19.14 < 6.20","Linux 7.0"],"published":"2026-07-25","updated":"2026-10-30","sourceUpdated":"2026-10-30T12:27:58.969Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-64525","references":[{"url":"https://git.kernel.org/stable/c/bca6386dc08750fc7cdcbc7683473748ba3114b9"},{"url":"https://git.kernel.org/stable/c/91cc13978ab0bc6f669139f53e7e613a860d10e0"},{"url":"https://git.kernel.org/stable/c/d14ae8ef88c2c6590e107db61b6adce148cec7b3"},{"url":"https://git.kernel.org/stable/c/3e52417318473782012b236d0325bf7d2266a597"}],"tags":["cve.org"],"epss":0.00156,"epssPercentile":0.04808,"ingestedAt":"2026-11-05T15:02:32.435Z","slug":"CVE-2026-64525","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nxfrm: move policy_bydst RCU sync from per-netns .exit to .pre_exit\n\nThe struct pernet_operations docstring in include/net/net_namespace.h\nexplicitly warns against blocking RCU primitives in .exit handlers:\n\n    Exit methods using blocking RCU primitives, such as\n    synchronize_rcu(), should be implemented via exit_batch.\n    [...]\n    Please, avoid synchronize_rcu() at all, where it's possible.\n\n    Note that a combination of pre_exit() and exit() can\n    be used, since a synchronize_rcu() is guaranteed between\n    the calls.\n\nxfrm_policy_fini() violates this: it calls synchronize_rcu() before\nfreeing the policy_bydst hash tables (so no RCU reader is mid-\ntraversal at free time), but runs from xfrm_net_ops.exit -- once per\nnamespace -- so a cleanup_net() of N namespaces pays N full RCU\ngrace periods serially.\n\nUse the documented pre_exit/exit split. Move the policy flush (and\nthe workqueue drains it depends on) into a new .pre_exit handler;\nxfrm_policy_fini() then runs in .exit and frees the hash tables\nafter the synchronize_rcu_expedited() that cleanup_net() guarantees\nbetween the two phases. Providing O(1) RCU grace periods per batch\ninstead of O(N).\n\nObserved on Linux 6.18 with a workload doing unshare(CLONE_NEWNET)\nat ~13/sec sustained: cleanup_net() and the netns_wq rescuer kthread\nboth stuck in xfrm_policy_fini()'s synchronize_rcu(), >300k struct\nnet accumulated in the cleanup queue, Percpu in /proc/meminfo climbed\nto 130+ GB on 256-CPU hosts, and memcg OOMs followed. setup_net and\n__put_net counts were balanced, ruling out a refcount leak.\n\n## Affected\n\n- `Linux >= 438b1f668ad58f46ce699bb48e4698a7839e3f9e < bca6386dc08750fc7cdcbc7683473748ba3114b9`\n- `Linux >= 3733fce2871c9bca9dd18a1a23b1432ea215a094 < 91cc13978ab0bc6f669139f53e7e613a860d10e0`\n- `Linux >= 069daad4f2ae9c5c108131995529d5f02392c446 < d14ae8ef88c2c6590e107db61b6adce148cec7b3`\n- `Linux >= 069daad4f2ae9c5c108131995529d5f02392c446 < 3e52417318473782012b236d0325bf7d2266a597`\n- `Linux b2faee12538b5b008eaef65a4201eb29cb5cefb3`\n- `Linux b66920a3348c0f63ba18365248fa21fbf0b3a937`\n- `Linux 33a3149dd81a1e2f52b80ee1e0fc380b39f3d028`\n- `Linux >= 6.12.83 < 6.12.93`\n- `Linux >= 6.18.24 < 6.18.35`\n- `Linux >= 6.1.191 < 6.2`\n- `Linux >= 6.6.136 < 6.7`\n- `Linux >= 6.19.14 < 6.20`\n- `Linux 7.0`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}