linux-kernel - Re: [PATCH -V18 04/13] vfs: Allow handle based open on symlinks

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20100820115135.GQ31363@ZenIV.linux.org.uk>
Date:	Fri, 20 Aug 2010 12:51:35 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Neil Brown <neilb@...e.de>
Cc:	Christoph Hellwig <hch@...radead.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	adilger@....com, corbet@....net, npiggin@...e.de,
	hooanon05@...oo.co.jp, bfields@...ldses.org, miklos@...redi.hu,
	linux-fsdevel@...r.kernel.org, sfrench@...ibm.com,
	philippe.deniel@....FR, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -V18 04/13] vfs: Allow handle based open on symlinks

On Fri, Aug 20, 2010 at 07:53:03PM +1000, Neil Brown wrote:
> On Fri, 20 Aug 2010 04:30:57 -0400
> Christoph Hellwig <hch@...radead.org> wrote:
> 
> > Suddenly getting an file pointer for a symlink which could never happen
> > before is a really bad idea.  Just add a proper readlink_by_handle
> > system call, similar to what's done in the XFS interface.
> 
> Why is that?
> With futexes we suddenly get a file descriptor for something we could never
> get a file descriptor on before and that doesn't seem to be a problem.
> 
> Why should symlinks be special as the only thing that you cannot have a file
> descriptor for?  Uniformity of interface is a very valuable property.

You are welcome to review the codepaths around pathname resolution for
assumptions of presense of ->follow_link() and friends; there _are_
subtle cases and dumping your "opened symlinks" in there is far from
a trivial change.  Note that it affects more than just the starting
points of lookups; /proc/*/fd/* stuff is also involved.

BTW, speaking of NULL pathname, linkat() variant that allows creating a link
to an opened file is also a very dubious thing; at the very least, you get
non-trivial security implications, since now a process that got an opened
descriptor passed to it by somebody else may create hardlinks to the sucker.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/