In the Linux kernel, the following vulnerability has been resolved: agp/amd64: Fix broken error propagation in agp_amd64_probe() A NULL pointer dereference was observed in the AMD64 AGP driver when running in a virtualized environment …

Overview

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

agp/amd64: Fix broken error propagation in agp_amd64_probe()

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 amd64_fetch_size() when attempting to dereference the pointer returned by node_to_amd_nb(0).

The root cause of this crash is broken error propagation in agp_amd64_probe(): 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 agp_add_bridge(), which invokes amd64_fetch_size(). Since the hardware does not exist, node_to_amd_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 agp_amd64_probe() 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.

Affected

• linux_kernel >= 2.6.18, < 5.10.260
• linux_kernel >= 5.11, < 5.15.211
• linux_kernel >= 5.16, < 6.1.177
• linux_kernel >= 6.2, < 6.6.144
• linux_kernel >= 6.7, < 6.12.95
• linux_kernel >= 6.13, < 6.18.37
• linux_kernel >= 6.19, < 7.0.14
• linux_kernel >= 7.1, < 7.1.2

Remediation

Upgrade past the affected range:

• linux_kernel 7.1.2