drivers/tty/n_tty.c in the Linux kernel before 4.14.11 allows local attackers (who are able to access pseudo terminals) to hang/block further usage of any pseudo terminal devices due to an EXTPROC versus ICANON confusion in TIOCINQ.
git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=966031f340185eddd05affcf72b740549f056348
access.redhat.com/errata/RHSA-2019:0831
bugzilla.suse.com/show_bug.cgi?id=1094825
cdn.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.14.11
github.com/torvalds/linux/commit/966031f340185eddd05affcf72b740549f056348
usn.ubuntu.com/3849-1/
usn.ubuntu.com/3849-2/