linux-kernel - Re: /proc/pid/fd && anon_inode

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Message-ID: <20130903155759.GB14734@amd.pavel.ucw.cz>
Date:	Tue, 3 Sep 2013 17:58:00 +0200
From:	Pavel Machek <pavel@....cz>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Al Viro <viro@...iv.linux.org.uk>, Willy Tarreau <w@....eu>,
	Oleg Nesterov <oleg@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	"security@...nel.org" <security@...nel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	Brad Spengler <spender@...ecurity.net>
Subject: Re: /proc/pid/fd && anon_inode_fops

Hi!

> > We are really stuck with the current semantics here - switching to
> > *BSD one would not only mean serious surgery on descriptor handling
> > (it's one of the wartier areas in *BSD VFS, in large part because
> > of magic-open-really-a-dup kludges they have to do), it would change
> > a long-standing userland API that had been there for nearly 20 years
> > _and_ one that tends to be used in corner cases of hell knows how many
> > scripts.
> 
> Actually, I'm pretty sure we did have the "dup" semantics at one point
> (long ago), and they were really nice (because you could use them to
> see where in the stream the fd was etc). It just fit so horribly badly
> into the VFS semantics that it got changed into the current "new file
> descriptor" one. Afaik, nothing broke.

Hmm, are you going to break my exploit?

http://www.exploit-db.com/exploits/10038/

I'd like that, because I don't think /proc should allow people to
bypass directory permissions.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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