# CVE-2026-64579: xfrm: policy: preallocate inexact bins before xfrm\_hash\_rebuild reinsert

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2026-08-05 · Updated: 2026-08-19

## Affected

- Linux: version range not reported
- Linux: 5.0

## Description

In the Linux kernel, the following vulnerability has been resolved: xfrm: policy: preallocate inexact bins before xfrm_hash_rebuild reinsert xfrm_hash_rebuild()'s first loop preallocates the bins/chains the reinsert loop needs, so the reinsert (after hlist_del_rcu()) cannot allocate or fail. But its guard is inverted: it skips policies with prefixlen < threshold and preallocates for the rest. prefixlen < threshold is exactly when policy_hash_bysel() returns NULL and the reinsert takes the allocating xfrm_policy_inexact_insert() path. So the loop preallocates for the exact policies (which never allocate) and skips the inexact ones, whose bin/node is then allocated GFP_ATOMIC during reinsert. On failure the error path only WARN_ONCE()s and continues, leaving a poisoned bydst node; the next rebuild's hlist_del_rcu() dereferences LIST_POISON2 and takes a GPF. Reachable under memory pressure, deterministic via failslab. Invert the guard so preallocation covers exactly the reinserted policies; the reinsert then allocates nothing and cannot fail. Crash: Oops: general protection fault, probably for non-canonical address 0xfbd59c0000000024: 0000 [#1] SMP KASAN NOPTI KASAN: maybe wild-memory-access in range [0xdead...] ... Workqueue: events xfrm_hash_rebuild RIP: 0010:xfrm_hash_rebuild+0x5b3/0x1190 RAX: dead000000000122 (LIST_POISON2 + offset) ... Call Trace: hlist_del_rcu (include/linux/rculist.h:599) xfrm_hash_rebuild (net/xfrm/xfrm_policy.c:1365) process_one_work (kernel/workqueue.c:3322) worker_thread (kernel/workqueue.c:3486) kthread (kernel/kthread.c:436) ret_from_fork (arch/x86/kernel/process.c:158) ret_from_fork_asm (arch/x86/entry/entry_64.S:245) ... Kernel panic - not syncing: Fatal exception in interrupt

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
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## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/e48f4c3e3df35b34be719d72d737bbeaca77cf0c
- https://git.kernel.org/stable/c/1cdeed9df1306f1a277e715600772640d63defa9
- https://git.kernel.org/stable/c/43a4d510523779891cf8eca7ffb4a086b0b5d8bf
- https://git.kernel.org/stable/c/d9d9cc21cc90014724a14c447e3d587be9447107
- https://git.kernel.org/stable/c/94c00391a5117530188334f740ce26d3f1256190
- https://git.kernel.org/stable/c/7acc5ed2f33608a3d83b64f50a5766843b6e2485
- https://git.kernel.org/stable/c/6aa3796d18a9fda953ad76a62b57bf6c145cb9ef
- https://git.kernel.org/stable/c/f38f8cce2f7e79775b3db7e8a5eacda04ac908e4

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