Re: [PATCH v10 08/17] tpm: call tpm2_flush_space() on error in tpm_try_transmit()

James Bottomley
2019-01-29T19:02:22Z

On Tue, 2019-01-29 at 20:53 +0200, Jarkko Sakkinen wrote:
> On Tue, Jan 29, 2019 at 09:06:01AM -0800, James Bottomley wrote:
> > On Wed, 2019-01-16 at 23:23 +0200, Jarkko Sakkinen wrote:
> > [...]
> > > - rc = tpm2_commit_space(chip, space, ordinal, buf, &len);
> > > +out_space:
> > > + if (rc)
> > > + tpm2_flush_space(chip);
> > > + else
> > > + rc = tpm2_commit_space(chip, space, ordinal,
> > > buf,
> > > &len);
> >
> > I don't think this is quite right. tpm2_flush_space only flushes
> > the handles it knows about and those are the ones from before the
> > TPM operation was attempted. If the operation has altered the
> > internal state we could miss a created handle in this flush and it
> > would effectively reside forever in the TPM. We should be able to
> > rely on the TPM preserving the original state if it returns an
> > error, so I think your patch works for that part. However rc is
> > also set to -EFAULT on a transmission error and if that's on the
> > receive path, the TPM may have changed state before the error
> > occurred.
>
> If TPM is working properly in the first place, tpm2_commit_space() is
> always called (e.g. in a situation where TPM gives a TPM error). Your
> deduction about the opposite is absolutely correct. Thanks!
>
> > If the object is to move the TPM back to where it was before the
> > error occurred, even in the case of transmit errors, then I think
> > we need to invent a new kind of flush that queries the current TPM
> > state and then flushes everything.
>
> I think this consideration is anyway out of scope for this patch set.

I certainly agree the problem existed before and this makes it no
worse.

> I'd hope you would also skim through v11 as soon as I get it
> prepared, at least the patches where I've added an explicit CC (one
> or two at most).

Sure, as you can see, I'm up to 8. I'll complete the review and then
set up an environment to test.

James