Looks like a Time of Check vs Time of Use (TOCTOU) type vulnerability. User controlled memory is read and used later by kernel space - time in between read and use can be used to overwrite it from user space, typically by exploiting and winning race conditions.

I haven't completed reading this one thoroughly but one example like this is kernel performing access checks on user requests asking it to perform some action - user space would ask for something it is permitted to do at first, kernel would read it and proceed to perform access check. User space meanwhile writes something different to the original memory area that specified the action - this time something privileged - kernel comes back successfully performing the access check for the older action and now executes the privileged action from the overwrite.

j00ru/project zero used modified Bochs (BochsPWN) to detect double memory fetch patterns to find similar vulnerabilities in the Windows kernel.