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From: Paul Moore <paul@paul-moore.com>
To: Jonathan Lebon <jlebon@redhat.com>
Cc: selinux@vger.kernel.org, Victor Kamensky <kamensky@cisco.com>
Subject: Re: [PATCH] selinux: allow labeling before policy is loaded
Date: Wed, 11 Sep 2019 19:56:28 -0400
Message-ID: <CAHC9VhSf6bD7iLmFEp78RuUT5g+f0tC_90L5cQ7hB+vwzPjbKQ@mail.gmail.com> (raw)
In-Reply-To: <CACpbjYoR19bm2-DDJafnSNPcEt6XLK-ZFBCJ6=UpBQDmnSVKwg@mail.gmail.com>

On Wed, Sep 11, 2019 at 5:28 PM Jonathan Lebon <jlebon@redhat.com> wrote:
> On Tue, Aug 27, 2019 at 8:56 PM Paul Moore <paul@paul-moore.com> wrote:
> > As I'm looking at this, I'm wondering why we don't just bail out early
> > if the policy isn't loaded?  The context lookup and permission checks
> > later in the function are pretty much useless if the policy hasn't
> > been loaded (they are just going to return defaults/allow), I think
> > the only thing we would need to check would be
> > inode_owner_or_capable().
>
> Yes, I think you're correct. Though in that case, would it make sense
> to just do the inode_owner_or_capable() check once upfront instead?
>
>   int selinux_inode_setxattr(...)
>   {
>
>     if (strcmp(name, XATTR_NAME_SELINUX)) {
>       ...
>     }
>
>     if (!inode_owner_or_capable(inode)
>       ...
>
>     if (!selinux_state.initialized)
>       return 0;
>
>     if (sbsec & SBLABEL_MNT)
>       ...
>
>     ...
>   }
>
> Hmm, though I guess it does change the behaviour slightly even in the
> initialized case by returning EPERM first where before we might've
> returned EOPNOTSUPP (I've seen userspace code which subtly relied on
> the order in which the kernel checks for error conditions). I'm happy
> to be conservative and go with your approach if you prefer.

Exactly.  I suggested the approach I did because I was trying to avoid
changing the return behaviour; unless you can prove beyond a shadow of
a doubt that changing the return values doesn't break anything (that's
a pretty high bar), stick with the conservative approach.

-- 
paul moore
www.paul-moore.com

      reply index

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-19 19:30 Jonathan Lebon
2019-08-19 19:49 ` Dominick Grift
2019-08-19 20:05 ` Dominick Grift
2019-08-19 21:11   ` Jonathan Lebon
2019-08-28  0:55 ` Paul Moore
2019-09-11 21:28   ` Jonathan Lebon
2019-09-11 23:56     ` Paul Moore [this message]

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