Linux kernel (drivers/gpu/drm/nouveau): Importing a dma-buf whose backing buffer object fails to initialize leaves the

Impact

Importing a dma-buf whose backing buffer object fails to initialize leaves the driver taking a reference on memory TTM has already freed - a use-after-free driven entirely from the PRIME import path. A tenant that can make buffer-object init fail (memory pressure, oversized or badly aligned imports) gets a freed-object reference count bumped under its control.

Who can reach it

A tenant process holding /dev/dri/renderD* on a nouveau GPU calls the PRIME/dma-buf import ioctl on a descriptor it crafted, repeatedly, under memory pressure it creates itself. Requires nouveau to be the driver in use for the NVIDIA card (not the proprietary stack), which is the case for hosts running the open upstream driver.

What to do

Boot a kernel carrying the nouveau prime import fix below. Interim: if the node runs nouveau, drop /dev/dri/renderD* from untrusted containers or block dma-buf import from tenant workloads that do not need cross-device buffer sharing.

References