amdgpu UVD DpbSize Overflow

Vulnerability analysis

The UVD H.264 decode path computed the number of reference picture buffers from a table keyed by the H.264 level in the decode message, then clamped the result to a maximum of 17. An attacker can supply a decode message whose actual reference count (now read from the message) exceeds what the level-based table assumed, so the kernel allocates a buffer that is too small for the number of references the hardware will write. The fix replaces the level-derived estimate with the actual reference count from the decode message and rejects messages with more than 17 references instead of silently clamping, ensuring the allocated buffer always matches what the hardware uses. The vulnerable path is reached through the AMDGPU DRM device by a local process that can submit a video decode command; it requires access to the GPU render node and an AMD GPU with UVD support.