|umount in util-linux 2.8 to 2.12q, 2.13-pre1, and 2.13-pre2, and other
packages such as loop-aes-utils, allows local users with unmount
permissions to gain privileges via the -r (remount) option, which
causes the file system to be remounted with just the read-only flag,
which effectively clears the nosuid, nodev, and other flags.