CVE-2026-53325

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

agp/amd64: Fix broken error propagation in agpamd64probe()

A NULL pointer dereference was observed in the AMD64 AGP driver when running in a virtualized environment (e.g. qemu/kvm) without a physical AMD northbridge. The crash occurs in amd64fetchsize() when attempting to dereference the pointer returned by nodetoamd_nb(0).

The root cause of this crash is broken error propagation in agpamd64probe(): When no AMD northbridges are found, cache_nbs() correctly returns -ENODEV. However, the probe function erroneously checks the return value against exactly -1, rather than < 0.

As a result, the hardware absence error is masked, allowing the driver to improperly proceed with initialization. It eventually calls agpaddbridge(), which invokes amd64fetchsize(). Since the hardware does not exist, nodetoamd_nb(0) returns NULL, leading to a General Protection Fault (GPF) when accessing its ->misc member.

Fix the issue by correcting the error check in agpamd64probe() to abort properly when cache_nbs() returns any negative error code. This prevents the driver from erroneously proceeding without hardware, thereby avoiding the subsequent NULL pointer dereference at its source.