The vmw_gb_surface_define_ioctl function (accessible via DRM_IOCTL_VMW_GB_SURFACE_CREATE) in drivers/gpu/drm/vmwgfx/vmwgfx_surface.c in the Linux kernel through 4.11.4 defines a backup_handle variable but does not give it an initial value. If one attempts to create a GB surface, with a previously allocated DMA buffer to be used as a backup buffer, the backup_handle variable does not get written to and is then later returned to user space, allowing local users to obtain sensitive information from uninitialized kernel memory via a crafted ioctl call.
http://www.debian.org/security/2017/dsa-3927
http://www.debian.org/security/2017/dsa-3945
http://www.securityfocus.com/bid/99095
https://github.com/torvalds/linux/commit/07678eca2cf9c9a18584e546c2b2a0d0c9a3150c
Source: MITRE
Published: 2017-06-13
Updated: 2017-11-04
Type: CWE-200
Base Score: 4.9
Vector: AV:L/AC:L/Au:N/C:C/I:N/A:N
Impact Score: 6.9
Exploitability Score: 3.9
Severity: MEDIUM
Base Score: 5.5
Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Impact Score: 3.6
Exploitability Score: 1.8
Severity: MEDIUM