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Date:   Fri, 23 Sep 2022 21:31:56 -0700
From:   Kees Cook <keescook@chromium.org>
To:     Evan Green <evgreen@chromium.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Gwendal Grignou <gwendal@chromium.org>,
        Eric Biggers <ebiggers@kernel.org>,
        Matthew Garrett <mgarrett@aurora.tech>,
        Jarkko Sakkinen <jarkko@kernel.org>,
        Mimi Zohar <zohar@linux.ibm.com>,
        linux-integrity@vger.kernel.org, Pavel Machek <pavel@ucw.cz>,
        apronin@chromium.org, Daniil Lunev <dlunev@google.com>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Linux PM <linux-pm@vger.kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        "James E.J. Bottomley" <jejb@linux.ibm.com>,
        Len Brown <len.brown@intel.com>,
        "Rafael J. Wysocki" <rafael@kernel.org>
Subject: Re: [PATCH v2 07/10] PM: hibernate: Use TPM-backed keys to encrypt
 image
Message-ID: <202209232130.ED110D8F7D@keescook>
References: <20220823222526.1524851-1-evgreen@chromium.org>
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 <202209201610.C06F8CA@keescook>
 <CAE=gft4twDMw8zpp1o0hv+SFFQtGNxkAivBg0VC2Pax1ez7qzg@mail.gmail.com>
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On Fri, Sep 23, 2022 at 03:23:43PM -0700, Evan Green wrote:
> On Tue, Sep 20, 2022 at 4:16 PM Kees Cook <keescook@chromium.org> wrote:
> > On Tue, Aug 23, 2022 at 03:25:23PM -0700, Evan Green wrote:
> > > [...]
> > > +     ret = key_instantiate_and_link(key, keyinfo, strlen(keyinfo) + 1, NULL,
> > > +                                    NULL);
> >
> > You want to keep the trailing NUL byte here so it's easier to read back
> > later? Reading it back will need to verify the trailing NUL regardless.
> > (Does this get read back?)
> 
> Are you referring to the trailing nul on keyinfo? The keyinfo string
> is only used within this function, as key_instantiate_and_link()
> receives it as a parameter string. I can see that
> trusted_instantiate() also null-terminates the buffer defensively for
> itself, but it still seemed prudent to hand in a terminated string. I
> can remove the + 1 if you think it's better.

No, I like having the trailing NUL byte -- it seems more robust that
way. I just wanted to understand who the consumer was going to be. I'm
clear now; thank you! :)

-- 
Kees Cook