linux-kernel - Re: [PATCH] nextfd(2)

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Message-ID: <CAOPLpQeJPxD4uVncY5tcheTizZzZ1xbWfwm1BKTqXMH56FP_3w@mail.gmail.com>
Date:	Mon, 2 Apr 2012 07:37:37 -0400
From:	Ulrich Drepper <drepper@...il.com>
To:	Kyle Moffett <kyle@...fetthome.net>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	akpm@...ux-foundation.org, viro@...iv.linux.org.uk,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] nextfd(2)

On Sun, Apr 1, 2012 at 21:19, Kyle Moffett <kyle@...fetthome.net> wrote:
> Well, I imagine one typical usecase for closing all FDs is for
> security isolation purposes (EG: chroot()+etc),

chroot and security in the same sentence...?

> and in a great deal of
> chroot environments you don't have /proc available.  In particular
> /proc has been a source of a lot of privilege escalations in the past,
> so avoiding mounting it in a chroot is good security policy if
> possible.

The problem is that the kernel exports quite a bit of information only
through the /proc and /sys filesystems.  I might try to finish my
comprehensive list of functionality depending on /proc sometime soon.
The list is quite long.

Not mounting /proc is inconvenient at best, it renders the environment
unusable quite often and in some cases is outright insecure..  I don't
think you can use not mounting /proc as an argument.  And, as Peter
said, the loop over the directory content is quite efficient.

If you want to avoid /proc I suggest you first work on removing the
dependencies.  Of just secure /proc itself.
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