High [CVE-2026-64525] move policy_bydst RCU sync from per-netns.exit to.pre_exit
This high-severity Red Hat Linux advisory covers CVE-2026-64525 affecting Red Hat Enterprise Linux 6, Red Hat package: kernel.
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Summary
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).
Affected products named by the advisory: Red Hat Enterprise Linux 6; Red Hat package: kernel.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · medium-confidence parse· fetched 10 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · medium-confidence parse· fetched 10 days ago·verify at source
Mitigation
The source record does not include mitigation steps. That is not a statement that no fix exists — read the vendor advisory below for the authoritative guidance.
Official advisory · medium-confidence parse· fetched 10 days ago·verify at source
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