linux-kernel - Re: symlinks with permissions

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Message-ID: <20091030203715.GA28901@emergent.ellipticsemi.com>
Date:	Fri, 30 Oct 2009 16:37:15 -0400
From:	Nick Bowler <nbowler@...iptictech.com>
To:	Pavel Machek <pavel@....cz>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Trond Myklebust <trond.myklebust@....uio.no>,
	Jan Kara <jack@...e.cz>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	"Serge E. Hallyn" <serue@...ibm.com>,
	kernel list <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org, viro@...iv.linux.org.uk,
	jamie@...reable.org
Subject: Re: symlinks with permissions

On 19:35 Fri 30 Oct     , Pavel Machek wrote:
> > How many linux shell scripts and other applications that use /dev/fd/N
> > or /proc/self/fd/N will you be breaking?
> 
> Zero. (Well unless someone is exploiting it in wild).

I've definitely written at least one script before that does something
along the lines of 'echo foo > /dev/fd/N'.  It's not one that I remember
anything else about, so perhaps its behaviour would be unaffected by
forbidding this if the particular file descriptor did not originally
have read-write permissions.  I have a hard time believing that amongst
millions of users, not one of them has a script that would be affected.

Frankly, I don't understand what is particularly surprising about the
fact that people can write to files with world write permissions.

-- 
Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/)

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