An issue was discovered in the Linux kernel through 4.17.10. There is an invalid pointer dereference in io_ctl_map_page() when mounting and operating a crafted btrfs image, because of a lack of block group item validation in check_leaf_item in fs/btrfs/tree-checker.c.
www.securityfocus.com/bid/104917
bugzilla.kernel.org/show_bug.cgi?id=199849
lists.debian.org/debian-lts-announce/2019/03/msg00017.html
lists.debian.org/debian-lts-announce/2020/06/msg00011.html
lists.debian.org/debian-lts-announce/2020/06/msg00013.html
patchwork.kernel.org/patch/10503147/
usn.ubuntu.com/3932-1/
usn.ubuntu.com/3932-2/
usn.ubuntu.com/4094-1/
usn.ubuntu.com/4118-1/
www.oracle.com/security-alerts/cpuApr2021.html