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References: <20221209195453.never.494-kees@kernel.org> <20221212211319.GA15511@mail.hallyn.com>
 <202212132006.F29BB81A@keescook>
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From:   Paul Moore <paul@paul-moore.com>
Date:   Thu, 15 Dec 2022 15:16:03 -0500
Message-ID: <CAHC9VhQ7DWQWqiMqHXQO==axnHr3qaxzD22wbK4R78saJt=P2w@mail.gmail.com>
Subject: Re: [PATCH] LoadPin: Ignore the "contents" argument of the LSM hooks
To:     Kees Cook <keescook@chromium.org>
Cc:     "Serge E. Hallyn" <serge@hallyn.com>,
        James Morris <jmorris@namei.org>,
        linux-security-module@vger.kernel.org,
        Mimi Zohar <zohar@linux.ibm.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
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On Tue, Dec 13, 2022 at 11:06 PM Kees Cook <keescook@chromium.org> wrote:
> On Mon, Dec 12, 2022 at 03:13:19PM -0600, Serge E. Hallyn wrote:
> > On Fri, Dec 09, 2022 at 11:54:57AM -0800, Kees Cook wrote:
> > > LoadPin only enforces the read-only origin of kernel file reads. Whether
> > > or not it was a partial read isn't important. Remove the overly
> > > conservative checks so that things like partial firmware reads will
> > > succeed (i.e. reading a firmware header).
> > >
> > > Fixes: 2039bda1fa8d ("LSM: Add "contents" flag to kernel_read_file hook")
> > > Cc: Paul Moore <paul@paul-moore.com>
> > > Cc: James Morris <jmorris@namei.org>
> > > Cc: "Serge E. Hallyn" <serge@hallyn.com>
> >
> > Acked-by: Serge Hallyn <serge@hallyn.com>
> >
> > Seems reasonable.
>
> Thanks!
>
> > So the patch which introduced this was
> > 2039bda1f: LSM: Add "contents" flag to kernel_read_file hook
> > It sounds like the usage of @contents which it added to ima still
> > makes sense.  But what about the selinux_kernel_read_file() one?
>
> I think those continue to make sense since those LSM may be sensitive to
> the _content_ (rather than the _origin_) of the file.

Agreed.  When @contents is false SELinux does a permission check
between the calling process and itself, but when @contents is true it
performs a check between the calling process and the file being read.

-- 
paul-moore.com