Linux kernel vmwgfx: integer overflow in the shader offset bound check lets an unbounded offset reach host SVGA commands

Impact

vmw_shader_define() validated the user-supplied shader window with an unsigned addition of size and offset; drm_vmw_shader_create_arg::offset is a __u64 in the uapi, so an offset near U64_MAX wraps and the check passes. The unbounded offset is then stored in res->guest_memory_offset and forwarded to the host in SVGA shader-create commands, which is a guest-to-host surface rather than a purely in-guest one. On virtualized infrastructure that means a local unprivileged user inside a VM feeds an out-of-range value across the guest/hypervisor boundary; the record does not characterize what the host does with it, so treat the ceiling as unproven and the exposure as real. Hosts do not run vmwgfx - only VMware guests do - so the affected population is your VM images, not the GPU nodes themselves.

Who can reach it

Local unprivileged user inside a VMware guest with access to a DRM render node on the vmwgfx driver. No authentication beyond an open of the device, which is normally world-accessible.

What to do

Update guest kernels to a build carrying the stable commits in the record, which use check_add_overflow() and compare the endpoint against the buffer size; the record names no fixed version. That means rebuilding or repatching VM images and rebooting each guest - a rolling workload restart, not a host maintenance window. Guests that have no use for vmwgfx render nodes can avoid exposing them.

References

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