CVE-2026-64531: net: openvswitch: reject oversized nested action attrs

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

net: openvswitch: reject oversized nested action attrs

Open vSwitch stores generated flow actions as nlattrs, whose nlalen field is u16. Commit a1e64addf3ff ("net: openvswitch: remove misbehaving actions length check") allowed the total swflowactions stream to grow beyond 64 KiB, which is valid, but also removed the last guard preventing a generated nested action attribute from exceeding U16MAX.

An oversized generated container can thus be closed with a truncated nlalen. A later dump or teardown then walks a structurally different stream than the one that was validated. In particular, an oversized nested CLONE/CT action may cause subsequent bytes in the generated stream to be interpreted as independent actions.

Keep the larger total-action-stream behavior, but make nested action close reject generated containers that do not fit in nlalen, and return the error through all callers. For recursive SAMPLE, CLONE, DECTTL, and CHECKPKTLEN builders, trim resource-owning action-list tails in reverse construction order before discarding failed wrappers, so resources copied into the rejected tails are released before the wrappers are removed.

Most failed outer wrappers are discarded by truncating actionslen after child resources have been released. CHECKPKTLEN also trims its parent after branch resources are gone. SET/TUNNEL close failures unwind their known tundst ownership directly, and SETTOMASKED has no external ownership and truncates on close failure.