The userfaultfd implementation in the Linux kernel before 4.19.7 mishandles access control for certain UFFDIO_ ioctl calls, as demonstrated by allowing local users to write data into holes in a tmpfs file (if the user has read-only access to that file, and that file contains holes), related to fs/userfaultfd.c and mm/userfaultfd.c.
Exploitability
AV:LAC:LPR:LUI:NScope
S:UImpact
C:NI:HA:N5.5/CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N