amdgpu IsolationIndex OOB

Vulnerability analysis

When a GPU ring is not assigned to a partition, the driver leaves its partition identifier set to a special "no partition" value. The driver then uses this value as an index into a per-partition array, causing an out-of-bounds access that triggers a kernel warning or crash. This happens during isolation enforcement and memory flush handling for SDMA work submissions. The fix treats unpartitioned rings as belonging to the first array slot, consistent with how the driver already handles shader cleanup, and only performs the array lookup for ring types that actually use isolation. A local user with access to the AMD GPU device can trigger this by submitting GPU work; the system must be using the amdgpu driver with a compatible AMD GPU.