Re: [PATCH] KEYS: trusted: Rollback init_trusted() consistently

[Jarkko Sakkinen <jarkko@kernel.org>]

On Wed, 2023-10-11 at 16:06 +0300, Jarkko Sakkinen wrote:
> On Wed, 2023-10-11 at 18:25 +0530, Sumit Garg wrote:
> > On Wed, 11 Oct 2023 at 18:07, Jarkko Sakkinen <jarkko@kernel.org> wrote:
> > > 
> > > On Wed, 2023-10-11 at 17:47 +0530, Sumit Garg wrote:
> > > > 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.
> > > 
> > > Yes, that does sounds reasonable.
> > > 
> > > About the debate. Well, it is better eagerly block and tree falls down
> > > somewhere we can consider extending the list through a fix.
> > > 
> > > This all wide open is worse than a few glitches somewhere, which are
> > > trivial to fix.
> > > 
> > 
> > Fair enough, I would suggest we document it appropriately such that it
> > is clear to the users or somebody looking at the code.
> 
> I went throught the backends on how they implement init:
> 
> 
CAAM:
> 1. Returns -ENODEV when it does not exist.
TEE:
> 2. Calls driver_register(). Something is wrong enough if that
>    fails to rollback the whole procedure.
> 3. TPM: -ENODEV

BR, Jarkko