linux-kernel - Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated devpts via path lookup

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Message-ID: <20160409140909.42315e6d@lxorguk.ukuu.org.uk>
Date:	Sat, 9 Apr 2016 14:09:09 +0100
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	ebiederm@...ssion.com (Eric W. Biederman)
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Hurley <peter@...leysoftware.com>,
	Greg KH <greg@...ah.com>, Jiri Slaby <jslaby@...e.com>,
	Aurelien Jarno <aurelien@...el32.net>,
	Andy Lutomirski <luto@...capital.net>,
	Florian Weimer <fw@...eb.enyo.de>,
	Al Viro <viro@...iv.linux.org.uk>,
	Serge Hallyn <serge.hallyn@...ntu.com>,
	Jann Horn <jann@...jh.net>,
	"security\@kernel.org" <security@...nel.org>,
	"security\@ubuntu.com \>\> security" <security@...ntu.com>,
	security@...ian.org, Willy Tarreau <w@....eu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 01/13] devpts: Teach /dev/ptmx to find the associated
 devpts via path lookup


> If anyone has a better idea on how userspace should connect the master
> pty file descriptor the slave file descriptor, I would be willing to
> implement that instead.

If we are willing to go away from the existing mess of a tty interface
inflicted on us by BSD and then mashed up by POSIX then a syscall of

  int err = ptypair(int fd[2], int perms, int flags);

[where flags is the O_ ones we usually need to cover (CLOEXEC etc) and
maybe even some kind of "private" flag to say don't even expose it via
devpts).

would do remarkably sane things to the majoirty of use cases as it breaks
the dependence on grantpt and also the historic screwup that pty pairs
aren't allocated atomically with both file handles returned as pipe()
does.

Alan