CVE-2026-64525
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.
How to fix
- Linux Linuxbca6386dc08750fc7cdcbc7683473748ba3114b9, 91cc13978ab0bc6f669139f53e7e613a860d10e0, d14ae8ef88c2c6590e107db61b6adce148cec7b3, 3e52417318473782012b236d0325bf7d2266a597, 6.12.93, 6.18.35, 6.2, 6.7, 6.20 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| Linux Linux | 438b1f668ad58f46ce699bb48e4698a7839e3f9e ≤ v < bca6386dc08750fc7cdcbc7683473748ba3114b9, 3733fce2871c9bca9dd18a1a23b1432ea215a094 ≤ v < 91cc13978ab0bc6f669139f53e7e613a860d10e0, 069daad4f2ae9c5c108131995529d5f02392c446 ≤ v < d14ae8ef88c2c6590e107db61b6adce148cec7b3, 069daad4f2ae9c5c108131995529d5f02392c446 ≤ v < 3e52417318473782012b236d0325bf7d2266a597, b2faee12538b5b008eaef65a4201eb29cb5cefb3, b66920a3348c0f63ba18365248fa21fbf0b3a937, 33a3149dd81a1e2f52b80ee1e0fc380b39f3d028, 6.12.83 ≤ v < 6.12.93, 6.18.24 ≤ v < 6.18.35, 6.1.191 ≤ v < 6.2, 6.6.136 ≤ v < 6.7, 6.19.14 ≤ v < 6.20, 7.0 | bca6386dc08750fc7cdcbc7683473748ba3114b9, 91cc13978ab0bc6f669139f53e7e613a860d10e0, d14ae8ef88c2c6590e107db61b6adce148cec7b3, 3e52417318473782012b236d0325bf7d2266a597, 6.12.93, 6.18.35, 6.2, 6.7, 6.20 |
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