CVE-2026-64525

Full vulnerability record from the local CVENow database.

Description

In the Linux kernel, the following vulnerability has been resolved: xfrm: move policy_bydst RCU sync from per-netns .exit to .pre_exit The struct pernet_operations docstring in include/net/net_namespace.h explicitly warns against blocking RCU primitives in .exit handlers: Exit methods using blocking RCU primitives, such as synchronize_rcu(), should be implemented via exit_batch. [...] Please, avoid synchronize_rcu() at all, where it's possible. Note that a combination of pre_exit() and exit() can be used, since a synchronize_rcu() is guaranteed between the calls. xfrm_policy_fini() violates this: it calls synchronize_rcu() before freeing the policy_bydst hash tables (so no RCU reader is mid- traversal at free time), but runs from xfrm_net_ops.exit -- once per namespace -- so a cleanup_net() of N namespaces pays N full RCU grace periods serially. Use the documented pre_exit/exit split. Move the policy flush (and the workqueue drains it depends on) into a new .pre_exit handler; xfrm_policy_fini() then runs in .exit and frees the hash tables after the synchronize_rcu_expedited() that cleanup_net() guarantees between the two phases. Providing O(1) RCU grace periods per batch instead of O(N). Observed on Linux 6.18 with a workload doing unshare(CLONE_NEWNET) at ~13/sec sustained: cleanup_net() and the netns_wq rescuer kthread both stuck in xfrm_policy_fini()'s synchronize_rcu(), >300k struct net accumulated in the cleanup queue, Percpu in /proc/meminfo climbed to 130+ GB on 256-CPU hosts, and memcg OOMs followed. setup_net and __put_net counts were balanced, ruling out a refcount leak.

Severity

Not scored

CVSS score

Not available

Vulnerability status

Received

Source identifier

416baaa9-dc9f-4396-8d5f-8c081fb06d67

Published

2026-07-25 10:17:38.830000

Last modified

2026-10-30 13:19:38.230000

View original CVE JSON

{
  "id": "CVE-2026-64525",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "published": "2026-07-25T10:17:38.830",
  "lastModified": "2026-10-30T13:19:38.230",
  "vulnStatus": "Received",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "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 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."
    }
  ],
  "affected": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "affectedData": [
        {
          "vendor": "Linux",
          "product": "Linux",
          "defaultStatus": "unaffected",
          "programFiles": [
            "net/xfrm/xfrm_policy.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "versions": [
            {
              "version": "438b1f668ad58f46ce699bb48e4698a7839e3f9e",
              "lessThan": "bca6386dc08750fc7cdcbc7683473748ba3114b9",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "3733fce2871c9bca9dd18a1a23b1432ea215a094",
              "lessThan": "91cc13978ab0bc6f669139f53e7e613a860d10e0",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "069daad4f2ae9c5c108131995529d5f02392c446",
              "lessThan": "d14ae8ef88c2c6590e107db61b6adce148cec7b3",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "069daad4f2ae9c5c108131995529d5f02392c446",
              "lessThan": "3e52417318473782012b236d0325bf7d2266a597",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "b2faee12538b5b008eaef65a4201eb29cb5cefb3",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "b66920a3348c0f63ba18365248fa21fbf0b3a937",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "33a3149dd81a1e2f52b80ee1e0fc380b39f3d028",
              "versionType": "git",
              "status": "affected"
            },
            {
              "version": "6.12.83",
              "lessThan": "6.12.93",
              "versionType": "semver",
              "status": "affected"
            },
            {
              "version": "6.18.24",
              "lessThan": "6.18.35",
              "versionType": "semver",
              "status": "affected"
            },
            {
              "version": "6.1.191",
              "lessThan": "6.2",
              "versionType": "semver",
              "status": "affected"
            },
            {
              "version": "6.6.136",
              "lessThan": "6.7",
              "versionType": "semver",
              "status": "affected"
            },
            {
              "version": "6.19.14",
              "lessThan": "6.20",
              "versionType": "semver",
              "status": "affected"
            }
          ]
        },
        {
          "vendor": "Linux",
          "product": "Linux",
          "defaultStatus": "affected",
          "programFiles": [
            "net/xfrm/xfrm_policy.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "versions": [
            {
              "version": "7.0",
              "status": "affected"
            },
            {
              "version": "0",
              "lessThan": "7.0",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "6.12.93",
              "lessThanOrEqual": "6.12.*",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "6.18.35",
              "lessThanOrEqual": "6.18.*",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "7.0.12",
              "lessThanOrEqual": "7.0.*",
              "versionType": "semver",
              "status": "unaffected"
            },
            {
              "version": "7.1",
              "lessThanOrEqual": "*",
              "versionType": "original_commit_for_fix",
              "status": "unaffected"
            }
          ]
        }
      ]
    }
  ],
  "metrics": {},
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/3e52417318473782012b236d0325bf7d2266a597",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/91cc13978ab0bc6f669139f53e7e613a860d10e0",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/bca6386dc08750fc7cdcbc7683473748ba3114b9",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/d14ae8ef88c2c6590e107db61b6adce148cec7b3",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ]
}