linux-kernel - Re: [PATCH 04/16] devpts: Teach /dev/ptmx to automount the appropriate devpts via path lookup

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Message-ID: <878u09mo7a.fsf@x220.int.ebiederm.org>
Date:	Tue, 19 Apr 2016 13:46:17 -0500
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Jann Horn <jann@...jh.net>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>, security@...ian.org,
	security@...nel.org, Al Viro <viro@...iv.linux.org.uk>,
	security@...ntu.com, Peter Hurley <peter@...leysoftware.com>,
	Serge Hallyn <serge.hallyn@...ntu.com>,
	Willy Tarreau <w@....eu>,
	Aurelien Jarno <aurelien@...el32.net>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Greg KH <greg@...ah.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jiri Slaby <jslaby@...e.com>, Florian Weimer <fw@...eb.enyo.de>
Subject: Re: [PATCH 04/16] devpts: Teach /dev/ptmx to automount the appropriate devpts via path lookup

Jann Horn <jann@...jh.net> writes:

> On Fri, Apr 15, 2016 at 10:35:20AM -0500, Eric W. Biederman wrote:
>> +static inline bool is_dev_ptmx(struct inode *inode)
>> +{
>> +	return inode->i_rdev == MKDEV(TTYAUX_MAJOR, PTMX_MINOR);
>> +}
>
> I'm not sure whether it matters, but I think a FUSE filesystem
> should be able to create a fake device that passes this check.
> fuse_init_inode() calls init_special_inode() with a user-supplied
> rdev for character devices. Is that a problem?

It isn't a problem with fuse, and I don't think it is a real problem
in general, but yes it would be good if that code had honored nodev
mount options.

Eric