Description
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.