Re: [PATCH v4] tpm_tis: Check return values from get_burstcount.

From: Josh Zimmerman <joshz-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
To: "Winkler, Tomas" <tomas.winkler-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Cc: "tpmdd-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org"
	<tpmdd-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org>
Subject: Re: [PATCH v4] tpm_tis: Check return values from get_burstcount.
Date: Thu, 27 Oct 2016 14:50:29 -0700	[thread overview]
Message-ID: <CAHSjozAcL7W-WN+Hf4LGBO8AsGQ+e3SG+VeKB0xnonrSt5SS_A@mail.gmail.com> (raw)
In-Reply-To: <5B8DA87D05A7694D9FA63FD143655C1B5430F484-Jy8z56yoSI8MvF1YICWikbfspsVTdybXVpNB7YpNyf8@public.gmane.org>

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Thanks, that's a fair point. Updated patch sent.

Josh

On Thu, Oct 27, 2016 at 1:31 PM, Winkler, Tomas <tomas.winkler-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
wrote:

> >
> > If the TPM we're connecting to uses a static burst count, it will report
> a burst
> > count of zero throughout the response read. However, get_burstcount
> assumes
> > that a response of zero indicates that the TPM is not ready to receive
> more
> > data. In this case, it returns a negative error code, which is passed on
> to
> > tpm_tis_{write,read}_bytes as a u16, causing them to read/write far too
> many
> > bytes.
> >
> > This patch checks for negative return codes and bails out from recv_data
> and
> > tpm_tis_send_data.
> >
> > Fixes: 1107d065fdf1 (tpm_tis: Introduce intermediate layer for TPM
> access)
> > Signed-off-by: Josh Zimmerman <joshz-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
> >
> > ---
> > Changelog v4:
> >  - Add short description to Fixes tag line.
> >  - Remove some unnecessary information in dev_err statements.
> > Changelog v3:
> >  - Add signed-off-by.
> > Changelog v2:
> >  - Fix typo (rc->burstcnt)
> >
> > ---
> >  drivers/char/tpm/tpm_tis_core.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_
> core.c
> > index e3bf31b..0f2c233 100644
> > --- a/drivers/char/tpm/tpm_tis_core.c
> > +++ b/drivers/char/tpm/tpm_tis_core.c
> > @@ -186,6 +186,10 @@ static int recv_data(struct tpm_chip *chip, u8 *buf,
> > size_t count)
> >                                chip->timeout_c,
> >                                &priv->read_queue, true) == 0) {
> >               burstcnt = min_t(int, get_burstcount(chip), count - size);
> > +             if (burstcnt < 0) {
>
> It is much more readable to directly check get_burstcount return value,
> 'count - size' is protected be above condition to not reach negative value.
>                              burstcnt = get_burstcount(chip)
>                              if (brustcnt < 0) ...
>
>
> > +                     dev_err(&chip->dev, "Unable to read burstcount\n");
> > +                     return burstcnt;
> > +             }
> >
> >               rc = tpm_tis_read_bytes(priv,
> TPM_DATA_FIFO(priv->locality),
> >                                       burstcnt, buf + size);
> > @@ -272,6 +276,11 @@ static int tpm_tis_send_data(struct tpm_chip *chip,
> u8
> > *buf, size_t len)
> >
> >       while (count < len - 1) {
> >               burstcnt = min_t(int, get_burstcount(chip), len - count -
> 1);
> > +             if (burstcnt < 0) {
> Same here
> > +                     dev_err(&chip->dev, "Unable to read burstcount\n");
> > +                     rc = burstcnt;
> > +                     goto out_err;
> > +             }
> >               rc = tpm_tis_write_bytes(priv,
> TPM_DATA_FIFO(priv->locality),
> >                                        burstcnt, buf + count);
> >               if (rc < 0)
> > --
> > 2.8.0.rc3.226.g39d4020
>
> Thanks
> Tomas
>

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