Re: [PATCH v4 6/6] tpm: ensure that the output of PCR read contains the correct digest size

[Roberto Sassu]

On 11/8/2018 3:08 PM, Jarkko Sakkinen wrote:
> On Tue, Nov 06, 2018 at 04:01:59PM +0100, Roberto Sassu wrote:
> > This patch protects against data corruption that could happen in the bus,
> > by checking that that the digest size returned by the TPM during a PCR read
> > matches the size of the algorithm passed as argument to tpm2_pcr_read().
> >
> > This check is performed after information about the PCR banks has been
> > retrieved.
> >
> > Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> > ---
> >   drivers/char/tpm/tpm2-cmd.c | 16 +++++++++++++++-
> >   1 file changed, 15 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
> > index e2d5b84286a7..3b0b5b032901 100644
> > --- a/drivers/char/tpm/tpm2-cmd.c
> > +++ b/drivers/char/tpm/tpm2-cmd.c
> > @@ -187,15 +187,28 @@ struct tpm2_pcr_read_out {
> >   int tpm2_pcr_read(struct tpm_chip *chip, int pcr_idx,
> >   		  struct tpm_digest *digest_struct, u16 *digest_size_ptr)
> >   {
> > +	int i;
> >   	int rc;
> >   	struct tpm_buf buf;
> >   	struct tpm2_pcr_read_out *out;
> >   	u8 pcr_select[TPM2_PCR_SELECT_MIN] = {0};
> >   	u16 digest_size;
> > +	u16 expected_digest_size = 0;
> >   
> >   	if (pcr_idx >= TPM2_PLATFORM_PCR)
> >   		return -EINVAL;
> >   
> > +	if (!digest_size_ptr) {
> > +		for (i = 0; i < chip->nr_active_banks &&
> > +		     chip->active_banks[i].alg_id != digest_struct->alg_id; i++)
> > +			;
>
> Not sure if the semicolon should be in its own line.

scripts/Lindent suggests:

for (i = 0; i < chip->nr_active_banks &&
     chip->active_banks[i].alg_id != digest_struct->alg_id;
     i++) ;

but this is not accepted by scripts/checkpatch.pl (there are no
warnings/errors on the patch I sent).


> > +
> > +		if (i == chip->nr_active_banks)
> > +			return -EINVAL;
> > +
> > +		expected_digest_size = chip->active_banks[i].digest_size;
> > +	}
> > +
> >   	rc = tpm_buf_init(&buf, TPM2_ST_NO_SESSIONS, TPM2_CC_PCR_READ);
> >   	if (rc)
> >   		return rc;
> > @@ -215,7 +228,8 @@ int tpm2_pcr_read(struct tpm_chip *chip, int pcr_idx,
> >   
> >   	out = (struct tpm2_pcr_read_out *)&buf.data[TPM_HEADER_SIZE];
> >   	digest_size = be16_to_cpu(out->digest_size);
> > -	if (digest_size > sizeof(digest_struct->digest)) {
> > +	if (digest_size > sizeof(digest_struct->digest) ||
> > +	    (!digest_size_ptr && digest_size != expected_digest_size)) {
> >   		rc = -EINVAL;
> >   		goto out;
> >   	}
> > --
> > 2.17.1
>
> Please add
>
> Cc: stable@xxxxxxxxxxxxxxxx
>
> /Jarkko

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