The sanity_check_ckpt function in fs/f2fs/super.c in the Linux kernel before 4.12.4 does not validate the blkoff and segno arrays, which allows local users to gain privileges via unspecified vectors.
https://source.android.com/security/bulletin/2017-08-01
https://github.com/torvalds/linux/commit/15d3042a937c13f5d9244241c7a9c8416ff6e82a
https://bugzilla.redhat.com/show_bug.cgi?id=1481149
http://www.securityfocus.com/bid/100215
http://www.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.12.4