On Fri, Jun 09, 2017 at 07:50:43PM +1000, Aleksa Sarai wrote: > > > When opening the slave end of a PTY, it is not possible for userspace to > > > safely ensure that /dev/pts/$num is actually a slave (in cases where the > > > mount namespace in which devpts was mounted is controlled by an > > > untrusted process). In addition, there are several unresolvable > > > race conditions if userspace were to attempt to detect attacks through > > > stat(2) and other similar methods [in addition it is not clear how > > > userspace could detect attacks involving FUSE]. > > > > > > Resolve this by providing an interface for userpace to safely open the > > > "peer" end of a PTY file descriptor by using the dentry cached by > > > devpts. Since it is not possible to have an open master PTY without > > > having its slave exposed in /dev/pts this interface is safe. This > > > interface currently does not provide a way to get the master pty (since > > > it is not clear whether such an interface is safe or even useful). > > > > > > Cc: Christian Brauner <christian.brauner@xxxxxxxxxx> > > > Cc: Valentin Rothberg <vrothberg@xxxxxxxx> > > > Signed-off-by: Aleksa Sarai <asarai@xxxxxxx> > > > > Is this going to be documented anywhere? Is there a man page update > > that also goes along with this? > > I will add one, I didn't know where the man-pages project is hosted / where > patches get pushed? What is the ML? >From the MAINTAINERS file: MAN-PAGES: MANUAL PAGES FOR LINUX -- Sections 2, 3, 4, 5, and 7 M: Michael Kerrisk <mtk.manpages@xxxxxxxxx> W: http://www.kernel.org/doc/man-pages L: linux-man@xxxxxxxxxxxxxxx S: Maintained > > What userspace program wants to use this? > > LXC (Christian is on Cc) will use this, runC will most likely use it, > pending on some design discussions (as well as some future container > runtimes I'm planning on working on). Effectively any container runtime that > wants to safely create terminals and spawn containers inside an existing > container's namespaces will likely want to use this. > > [ As an aside, I /would/ argue this is a security fix (it fixes an interface > problem that made doing certain operations securely possible) but I didn't > want to Cc stable@ because it's a feature and not a strict bugfix. ] Yeah, it's a new feature, so stable doesn't really fit here. And as people who use containers are all keeping up to date with their kernel versions, this shouldn't be that big of a deal, not like the Android kernel mess :) thanks, greg k-h
