by Sumit Garg

[permalink] [raw]

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

On Wed, 11 Oct 2023 at 19:35, Jarkko Sakkinen <[email protected]> wrote:
>
> On Wed, 2023-10-11 at 16:55 +0300, Jarkko Sakkinen wrote:
> > On Wed, 2023-10-11 at 19:12 +0530, Sumit Garg wrote:
> > > On Wed, 11 Oct 2023 at 18:36, Jarkko Sakkinen <[email protected]> wrote:
> > > >
> > > > On Wed, 2023-10-11 at 18:25 +0530, Sumit Garg wrote:
> > > > > On Wed, 11 Oct 2023 at 18:07, Jarkko Sakkinen <[email protected]> wrote:
> > > > > >
> > > > > > On Wed, 2023-10-11 at 17:47 +0530, Sumit Garg wrote:
> > > > > > > On Wed, 11 Oct 2023 at 16:04, Jarkko Sakkinen <[email protected]> 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 <[email protected]> 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 <[email protected]>
> > > > > > > > > > > Closes: https://lore.kernel.org/linux-integrity/CAHk-=whOPoLaWM8S8GgoOPT7a2+nMH5h3TLKtn=R_3w4R1_Uvg@mail.gmail.com/
> > > > > > > > > > > Cc: [email protected] # v5.13+
> > > > > > > > > > > Fixes: 5d0682be3189 ("KEYS: trusted: Add generic trusted keys framework")
> > > > > > > > > > > Signed-off-by: Jarkko Sakkinen <[email protected]>
> > > > > > > > > > > ---
> > > > > > > > > > > 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:
> > > >
> > > > 1. Returns -ENODEV when it does not exist.
> > > > 2. Calls driver_register(). Something is wrong enough if that
> > > > fails to rollback the whole procedure.
> > > > 3. TPM: -ENODEV
> > > >
> > > > Therefore, I would keep in the existing patch since there is no weird
> > > > uapi visible legacy behavior to support in the first place. And for
> > > > that reason there is no good reason to have all those four POSIX rc's
> > > > in the list.
> > >
> > > Okay I can live with this patch as long as it doesn't break the
> > > intended use-case.
> >
> > Well this sort of policy has been already existing for some time:
> >
> > /*
> > * encrypted_keys.ko depends on successful load of this module even if
> > * trusted key implementation is not found.
> > */
> > if (ret == -ENODEV)
> > return 0;
> >
> > If we would need a list of error codes, then this is also incorrect
> > implementation because the error codes that you listed should be
> > also success cases.
>

As I mentioned before we can go ahead with this policy for trust
sources and see how it pans out.

> The dead obvious constraint here is that whatever error codes are
> processed they need to be exact same anyway right?
>
> If things fall apart you should really not continue. This is IMHO
> categorizes as a critical bug,

Here we are discussing trust sources as multiple independent devices.
If a particular device probe/init fails then it shouldn't be a blocker
to probe/init another device.

> not just debatable aspect on how
> subsystems are engineered. I.e.I do not consider this as any sort
> of API discussion per se.

Agree, I see it as a policy decision for the trusted keys subsystem.

-Sumit

>
> BR, Jarkko