xfrm: move policy_bydst RCU sync from per-netns .exit to .pre_exit
Summary
| CVE | CVE-2026-64525 |
|---|---|
| State | PUBLISHED |
| Assigner | Linux |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-07-25 10:17:38 UTC |
| Updated | 2026-07-25 10:17:38 UTC |
| 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. |
Risk And Classification
EPSS: 0.001560000 probability, percentile 0.052520000 (date 2026-07-29)
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Linux | Linux | affected 438b1f668ad58f46ce699bb48e4698a7839e3f9e bca6386dc08750fc7cdcbc7683473748ba3114b9 git | Not specified |
| CNA | Linux | Linux | affected 3733fce2871c9bca9dd18a1a23b1432ea215a094 91cc13978ab0bc6f669139f53e7e613a860d10e0 git | Not specified |
| CNA | Linux | Linux | affected 069daad4f2ae9c5c108131995529d5f02392c446 d14ae8ef88c2c6590e107db61b6adce148cec7b3 git | Not specified |
| CNA | Linux | Linux | affected 069daad4f2ae9c5c108131995529d5f02392c446 3e52417318473782012b236d0325bf7d2266a597 git | Not specified |
| CNA | Linux | Linux | affected b66920a3348c0f63ba18365248fa21fbf0b3a937 git | Not specified |
| CNA | Linux | Linux | affected 33a3149dd81a1e2f52b80ee1e0fc380b39f3d028 git | Not specified |
| CNA | Linux | Linux | affected 6.12.83 6.12.93 semver | Not specified |
| CNA | Linux | Linux | affected 6.18.24 6.18.35 semver | Not specified |
| CNA | Linux | Linux | affected 6.6.136 6.7 semver | Not specified |
| CNA | Linux | Linux | affected 6.19.14 6.20 semver | Not specified |
| CNA | Linux | Linux | affected 7.0 | Not specified |
| CNA | Linux | Linux | unaffected 7.0 semver | Not specified |
| CNA | Linux | Linux | unaffected 6.12.93 6.12.* semver | Not specified |
| CNA | Linux | Linux | unaffected 6.18.35 6.18.* semver | Not specified |
| CNA | Linux | Linux | unaffected 7.0.12 7.0.* semver | Not specified |
| CNA | Linux | Linux | unaffected 7.1 * original_commit_for_fix | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| git.kernel.org/stable/c/d14ae8ef88c2c6590e107db61b6adce148cec7b3 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/3e52417318473782012b236d0325bf7d2266a597 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/91cc13978ab0bc6f669139f53e7e613a860d10e0 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| git.kernel.org/stable/c/bca6386dc08750fc7cdcbc7683473748ba3114b9 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 | git.kernel.org | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
No vendor comments have been submitted for this CVE.
There are currently no legacy QID mappings associated with this CVE.