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From:   Sumit Garg <sumit.garg@linaro.org>
Date:   Wed, 11 Oct 2023 17:47:11 +0530
Message-ID: <CAFA6WYObvJvQv=-JJ5gnmFqJKbT=4JnT+ErC=iB1KfnYfVn7Ag@mail.gmail.com>
Subject: Re: [PATCH] KEYS: trusted: Rollback init_trusted() consistently
To:     Jarkko Sakkinen <jarkko@kernel.org>
Cc:     keyrings@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        stable@vger.kernel.org, James Bottomley <jejb@linux.ibm.com>,
        Mimi Zohar <zohar@linux.ibm.com>,
        David Howells <dhowells@redhat.com>,
        Paul Moore <paul@paul-moore.com>,
        James Morris <jmorris@namei.org>,
        "Serge E. Hallyn" <serge@hallyn.com>,
        "open list:KEYS-TRUSTED" <linux-integrity@vger.kernel.org>,
        "open list:SECURITY SUBSYSTEM" 
        <linux-security-module@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
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On Wed, 11 Oct 2023 at 16:04, Jarkko Sakkinen <jarkko@kernel.org> wrote:
>
> On Wed, 2023-10-11 at 13:12 +0300, Jarkko Sakkinen wrote:
> > On Wed, 2023-10-11 at 11:27 +0530, Sumit Garg wrote:
> > > On Wed, 11 Oct 2023 at 04:46, Jarkko Sakkinen <jarkko@kernel.org> wrote:
> > > >
> > > > Do bind neither static calls nor trusted_key_exit() before a successful
> > > > init, in order to maintain a consistent state. In addition, depart the
> > > > init_trusted() in the case of a real error (i.e. getting back something
> > > > else than -ENODEV).
> > > >
> > > > Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
> > > > Closes: https://lore.kernel.org/linux-integrity/CAHk-=whOPoLaWM8S8GgoOPT7a2+nMH5h3TLKtn=R_3w4R1_Uvg@mail.gmail.com/
> > > > Cc: stable@vger.kernel.org # v5.13+
> > > > Fixes: 5d0682be3189 ("KEYS: trusted: Add generic trusted keys framework")
> > > > Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
> > > > ---
> > > >  security/keys/trusted-keys/trusted_core.c | 20 ++++++++++----------
> > > >  1 file changed, 10 insertions(+), 10 deletions(-)
> > > >
> > > > diff --git a/security/keys/trusted-keys/trusted_core.c b/security/keys/trusted-keys/trusted_core.c
> > > > index 85fb5c22529a..fee1ab2c734d 100644
> > > > --- a/security/keys/trusted-keys/trusted_core.c
> > > > +++ b/security/keys/trusted-keys/trusted_core.c
> > > > @@ -358,17 +358,17 @@ static int __init init_trusted(void)
> > > >                 if (!get_random)
> > > >                         get_random = kernel_get_random;
> > > >
> > > > -               static_call_update(trusted_key_seal,
> > > > -                                  trusted_key_sources[i].ops->seal);
> > > > -               static_call_update(trusted_key_unseal,
> > > > -                                  trusted_key_sources[i].ops->unseal);
> > > > -               static_call_update(trusted_key_get_random,
> > > > -                                  get_random);
> > > > -               trusted_key_exit = trusted_key_sources[i].ops->exit;
> > > > -               migratable = trusted_key_sources[i].ops->migratable;
> > > > -
> > > >                 ret = trusted_key_sources[i].ops->init();
> > > > -               if (!ret)
> > > > +               if (!ret) {
> > > > +                       static_call_update(trusted_key_seal, trusted_key_sources[i].ops->seal);
> > > > +                       static_call_update(trusted_key_unseal, trusted_key_sources[i].ops->unseal);
> > > > +                       static_call_update(trusted_key_get_random, get_random);
> > > > +
> > > > +                       trusted_key_exit = trusted_key_sources[i].ops->exit;
> > > > +                       migratable = trusted_key_sources[i].ops->migratable;
> > > > +               }
> > > > +
> > > > +               if (!ret || ret != -ENODEV)
> > >
> > > As mentioned in the other thread, we should allow other trust sources
> > > to be initialized if the primary one fails.
> >
> > I sent the patch before I received that response but here's what you
> > wrote:
> >
> > "We should give other trust sources a chance to register for trusted
> > keys if the primary one fails."
> >
> > 1. This condition is lacking an inline comment.
> > 2. Neither this response or the one that you pointed out has any
> >    explanation why for any system failure the process should
> >    continue.
> >
> > You should really know the situations (e.g. list of posix error
> > code) when the process can continue and "allow list" those. This
> > way way too abstract. It cannot be let all possible system failures
> > pass.
>
> And it would nice if it printed out something for legit cases. Like
> "no device found" etc. And for rest it must really withdraw the whole
> process.

IMO, it would be quite tricky to come up with an allow list. Can we
keep "EACCES", "EPERM", "ENOTSUPP" etc in that allow list? I think
these are all debatable.

The original intention to iterate through the trust source list was to
allow a single Linux kernel binary to support platforms with varying
trust sources (one or choose one from multiple) available. IMO, any
restriction on the basis of error codes here since we can't predict
them correctly may forfeit this intended use-case.

-Sumit

>
> BR, Jarkko