tpm_tis: Check return values from get_burstcount.

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.

Cc: stable@vger.kernel.org
Fixes: 1107d065fdf1 (tpm_tis: Introduce intermediate layer for TPM access)
Signed-off-by: Josh Zimmerman <joshz@google.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>

1 files changed, 13 insertions, 2 deletions

diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
index 73f4c4bbc4df..2d1e451fb1b3 100644
--- a/drivers/char/tpm/tpm_tis_core.c
+++ b/drivers/char/tpm/tpm_tis_core.c
@@ -187,7 +187,12 @@ static int recv_data(struct tpm_chip *chip, u8 *buf, size_t count)
                                  &priv->read_queue, true);
                 if (rc < 0)
                         return rc;
-                burstcnt = min_t(int, get_burstcount(chip), count - size);
+                burstcnt = get_burstcount(chip);
+                if (burstcnt < 0) {
+                        dev_err(&chip->dev, "Unable to read burstcount\n");
+                        return burstcnt;
+                }
+                burstcnt = min_t(int, burstcnt, count - size);
 
                 rc = tpm_tis_read_bytes(priv, TPM_DATA_FIFO(priv->locality),
                                         burstcnt, buf + size);
@@ -276,7 +281,13 @@ 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);
+                burstcnt = get_burstcount(chip);
+                if (burstcnt < 0) {
+                        dev_err(&chip->dev, "Unable to read burstcount\n");
+                        rc = burstcnt;
+                        goto out_err;
+                }
+                burstcnt = min_t(int, burstcnt, len - count - 1);
                 rc = tpm_tis_write_bytes(priv, TPM_DATA_FIFO(priv->locality),
                                          burstcnt, buf + count);
                 if (rc < 0)