CVE-2026-64474: vfio: prevent infinite loop in vfio_mig_get_next_state() on blocked arc

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

vfio: prevent infinite loop in vfiomiggetnextstate() on blocked arc

vfiomiggetnextstate() walks vfiofromfsmtable[] one step at a time, looping to skip optional states the device does not support until nextfsm is supported. A blocked transition is encoded as VFIODEVICESTATEERROR, which the trailing return reports as -EINVAL.

The skip loop does not account for the ERROR sentinel. stateflagstable[ERROR] is ~0U and vfiofromfsmtable[ERROR][] is ERROR, so once nextfsm becomes ERROR the loop condition stays true and nextfsm never changes. The blocked arcs STOPCOPY -> PRECOPY and STOPCOPY -> PRECOPYP2P map to ERROR yet pass the support check on a precopy-capable device, causing the loop to spin forever while holding the driver state mutex. This can result in a soft lockup, and a panic with softlockuppanic set.

Terminate the skip loop on the ERROR sentinel so a blocked transition falls through to the existing return and reports -EINVAL.