CVE-2026-31663 — xfrm: hold dev ref until after transport_finish NF_HOOK

Affected: Linux, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7

In the Linux kernel, the following vulnerability has been resolved:

xfrm: hold dev ref until after transport_finish NF_HOOK

After async crypto completes, xfrm_input_resume() calls dev_put() immediately on re-entry before the skb reaches transport_finish. The skb->dev pointer is then used inside NF_HOOK and its okfn, which can race with device teardown.

Remove the dev_put from the async resumption entry and instead drop the reference after the NF_HOOK call in transport_finish, using a saved device pointer since NF_HOOK may consume the skb. This covers NF_DROP, NF_QUEUE and NF_STOLEN paths that skip the okfn.

For non-transport exits (decaps, gro, drop) and secondary async return points, release the reference inline when async is set.

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CVE-2026-31663 — xfrm: hold dev ref until after transport_finish NF_HOOK