linux-kernel - Re: [PATCH v3 1/1] dcache: Translating dentry into pathname without taking rename

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: <20130907000044.GX13318@ZenIV.linux.org.uk>
Date:	Sat, 7 Sep 2013 01:00:44 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Waiman Long <Waiman.Long@...com>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Chandramouleeswaran, Aswin" <aswin@...com>,
	"Norton, Scott J" <scott.norton@...com>,
	George Spelvin <linux@...izon.com>,
	John Stoffel <john@...ffel.org>
Subject: Re: [PATCH v3 1/1] dcache: Translating dentry into pathname without
 taking rename_lock

On Fri, Sep 06, 2013 at 02:48:32PM -0700, Linus Torvalds wrote:
> On Fri, Sep 6, 2013 at 2:05 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
> >
> > I can take that, but I'm really not convinced that we need writer lock
> > there at all.  After all, if we really can get livelocks on that one,
> > we would be getting them on d_lookup()...
> 
> d_lookup() does a _single_ path component. That's a *big* difference.
> 
> Sure, the hash chain that d_lookup() (well, __d_lookup()) ends up
> walking is a bit more complicated than just following the dentry
> parent pointer, but that's much harder to trigger than just creating a
> really deep directory structure of single-letter nested directories,
> and then doing a "getcwd()" that walks 1024+ parents, while another
> thread is looping renaming things..
> 
> So I personally do feel a lot safer with the fallback to write locking here.
> 
> Especially since it's pretty simple, so there isn't really much downside.

Er... what will happen if you have done just what you've described and have
a process call d_lookup()?
--
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/