Re: [PATCH] tpm: fix incorrect success returns from tpm_try_transmit()

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Thu, 2019-01-03 at 14:59 +0200, Jarkko Sakkinen wrote:
> On Mon, Dec 31, 2018 at 10:27:31AM -0800, James Bottomley wrote:
> > Ever since 627448e85c766 "tpm: separate cmd_ready/go_idle from
> > runtime_pm" we have been returning success from tpm_try_transmit()
> > even if an error occurred.  The reason is that the introduction of
> > rc
> > = tpm_go_idle() at the end of processing overwrites the value of rc
> > if
> > it contains an error code (mostly with success).  Fix this by
> > writing
> > the return to a new variable rc1 instead.
> > 
> > Fixes: 627448e85c766 "tpm: separate cmd_ready/go_idle from
> > runtime_pm"
> > Cc: stable@vger.kernel.org
> > Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.c
> > om>
> > 
> > ---
> > 
> > Note: the goto out looks fishy as well.  The only go_idle
> > implementor
> > is tpm_crb and that can return a timeout as -ETIME, so it looks
> > like it
> > would then loop forever
> > 
> > diff --git a/drivers/char/tpm/tpm-interface.c
> > b/drivers/char/tpm/tpm-interface.c
> > index 129f640424b7..ac7ebab6140c 100644
> > --- a/drivers/char/tpm/tpm-interface.c
> > +++ b/drivers/char/tpm/tpm-interface.c
> > @@ -432,7 +432,7 @@ static ssize_t tpm_try_transmit(struct tpm_chip
> > *chip,
> >  				unsigned int flags)
> >  {
> >  	struct tpm_output_header *header = (void *)buf;
> > -	int rc;
> > +	int rc, rc1;
> >  	ssize_t len = 0;
> >  	u32 count, ordinal;
> >  	unsigned long stop;
> > @@ -547,8 +547,8 @@ static ssize_t tpm_try_transmit(struct tpm_chip
> > *chip,
> >  		dev_err(&chip->dev, "tpm2_commit_space: error
> > %d\n", rc);
> >  
> >  out:
> > -	rc = tpm_go_idle(chip, flags);
> > -	if (rc)
> > +	rc1 = tpm_go_idle(chip, flags);
> > +	if (rc1)
> >  		goto out;
> >  
> >  	if (need_locality)
> 
> Thanks James and sorry for latency (holiday season). Just a small
> suggestion. I would just:
> 
> if (tpm_go_idle(chip, flags))
> 	goto out;
> 
> What do you think?

That it doesn't solve the loop forever with no warning problem.  If
anything, I think the correct thing is probably

	rc1 = tpm_go_idle(chip, flags);
	if (rc1)
  		dev_err(&chip->dev, "go idle failed with %d\n", rc1);

so we log the problem and move on.  If it is a timeout, it will likely
show up on the next TPM operation.  Since this is the only caller of
tpm_go_idle(), I think all looping should be done inside that function,
but we should probably wait for Tomas to comment since he wrote it.

James