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Message-ID: <CAGXu5j+8KMdX92T6Ma8HBXko4BHGmZKcV1kuR+b38r00r6YZbw@mail.gmail.com>
Date: Sun, 1 Jul 2012 17:43:22 -0700
From: Kees Cook <keescook@...omium.org>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
linux-fsdevel@...r.kernel.org, Eric Paris <eparis@...hat.com>,
Matthew Wilcox <matthew@....cx>, Doug Ledford <dledford@...hat.com>, Joe Korty <joe.korty@...r.com>,
"Eric W. Biederman" <ebiederm@...ssion.com>, Ingo Molnar <mingo@...e.hu>,
David Howells <dhowells@...hat.com>, James Morris <james.l.morris@...cle.com>,
linux-doc@...r.kernel.org, Dan Rosenberg <drosenberg@...curity.com>,
kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH 1/2] fs: add link restrictions
On Sat, Jun 30, 2012 at 2:14 AM, Al Viro <viro@...iv.linux.org.uk> wrote:
> On Mon, Jun 25, 2012 at 02:05:26PM -0700, Kees Cook wrote:
>
>> +config PROTECTED_LINKS
>> + bool "Evaluate vulnerable link conditions"
>> + default y
>
> Remember Linus' rants about 'default y' in general?
I added these configs due to other people's requests. I am happy to
remove them all and have the sysctls start their life == 1. It would
eliminate all the #ifdef logic too.
>> + /* Check parent directory mode and owner. */
>
> I suspect that we ought to simply pass that parent directory as argument - caller
> *does* have a reference to it, so we don't need to mess with ->d_lock, etc.
I don't see where the parent is held in either path_openat nor
path_lookupat. What should I be passing into may_follow_link() for the
parent?
>> + err = may_follow_link(&link);
>> + if (unlikely(err))
>> + break;
>
> No. This is definitely wrong - you are leaking dentries and vfsmount here.
What should I do to avoid the leak? I thought it was avoiding the need
to call put_link because it aborts before calling follow_link.
>> + error = may_follow_link(&link);
>> + if (unlikely(error))
>> + break;
>
> Ditto.
Same thing here -- it aborts before the follow_link. I must be
misunderstanding something. What am I missing?
Thanks for the feedback! I'll clean up the other things you mentioned as well.
-Kees
--
Kees Cook
Chrome OS Security
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