The Linux kernel before 5.1-rc5 allows page->_refcount reference count overflow, with resultant use-after-free issues, if about 140 GiB of RAM exists. This is related to fs/fuse/dev.c, fs/pipe.c, fs/splice.c, include/linux/mm.h, include/linux/pipe_fs_i.h, kernel/trace/trace.c, mm/gup.c, and mm/hugetlb.c. It can occur with FUSE requests.
https://www.oracle.com/security-alerts/cpuApr2021.html
https://usn.ubuntu.com/4145-1/
https://usn.ubuntu.com/4118-1/
https://usn.ubuntu.com/4115-1/
https://usn.ubuntu.com/4069-2/
https://usn.ubuntu.com/4069-1/
https://support.f5.com/csp/article/K14255532
https://security.netapp.com/advisory/ntap-20190517-0005/
https://lwn.net/Articles/786044/
https://lists.debian.org/debian-lts-announce/2019/09/msg00015.html
https://lists.debian.org/debian-lts-announce/2019/09/msg00014.html
https://github.com/torvalds/linux/commit/f958d7b528b1b40c44cfda5eabe2d82760d868c3
https://github.com/torvalds/linux/commit/8fde12ca79aff9b5ba951fce1a2641901b8d8e64
https://github.com/torvalds/linux/commit/88b1a17dfc3ed7728316478fae0f5ad508f50397
https://github.com/torvalds/linux/commit/6b3a707736301c2128ca85ce85fb13f60b5e350a
https://github.com/torvalds/linux/commit/15fab63e1e57be9fdb5eec1bbc5916e9825e9acb
https://bugs.chromium.org/p/project-zero/issues/detail?id=1752
https://access.redhat.com/errata/RHSA-2020:0174
https://access.redhat.com/errata/RHSA-2019:2741
https://access.redhat.com/errata/RHSA-2019:2703
http://www.securityfocus.com/bid/108054
http://www.openwall.com/lists/oss-security/2019/04/29/1
http://lists.opensuse.org/opensuse-security-announce/2019-06/msg00048.html
http://lists.opensuse.org/opensuse-security-announce/2019-06/msg00040.html
http://lists.opensuse.org/opensuse-security-announce/2019-06/msg00039.html