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.

Fixes 1107d065fdf1 (tpm_tis: Introduce intermediate layer for TPM access)

Signed-off-by Josh Zimmerman <[email protected]>

---
Changelog v5:
- Move burstcnt < 0 check to before the min_t() call for enhanced readability.
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 | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

drivers/char/tpm/tpm_tis_core.c +13 -2

index e3bf31b..a1ce060 100644
@@ -185,7 +185,12 @@ static int recv_data(struct tpm_chip *chip, u8 *buf, size_t count)
 				 TPM_STS_DATA_AVAIL | TPM_STS_VALID,
 				 chip->timeout_c,
 				 &priv->read_queue, true) == 0) {
-		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);

@@ -271,7 +276,13 @@ 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)

Signature · 1 line

2.8.0.rc3.226.g39d4020

Quoted 64 lines · Josh Zimmerman

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 <[email protected]>

---
Changelog v5:
- Move burstcnt < 0 check to before the min_t() call for enhanced readability.
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 | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

drivers/char/tpm/tpm_tis_core.c +13 -2

index e3bf31b..a1ce060 100644
@@ -185,7 +185,12 @@ static int recv_data(struct tpm_chip *chip, u8 *buf, size_t count)
 				 TPM_STS_DATA_AVAIL | TPM_STS_VALID,
 				 chip->timeout_c,
 				 &priv->read_queue, true) == 0) {
-		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);

@@ -271,7 +276,13 @@ 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)

Signature · 1 line

2.8.0.rc3.226.g39d4020

LGTM

Reviewed-by Jarkko Sakkinen <jarkko.sakkinen-VuQAYsv1563Yd54FQh9/[email protected]>

Quoted 68 lines · Jarkko Sakkinen

Quoted 64 lines · Josh Zimmerman

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 <[email protected]>

---
Changelog v5:
- Move burstcnt < 0 check to before the min_t() call for enhanced readability.
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 | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

drivers/char/tpm/tpm_tis_core.c +13 -2

index e3bf31b..a1ce060 100644
@@ -185,7 +185,12 @@ static int recv_data(struct tpm_chip *chip, u8 *buf, size_t count)
 				 TPM_STS_DATA_AVAIL | TPM_STS_VALID,
 				 chip->timeout_c,
 				 &priv->read_queue, true) == 0) {
-		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);

@@ -271,7 +276,13 @@ 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)

Signature · 1 line

2.8.0.rc3.226.g39d4020

LGTM

Quoted 1 line

Reviewed-by Jarkko Sakkinen <[email protected]>

I'm sorry for the delay with testing but I cannot test this during this week. The network connection is terrible at the Linux Plumbers Conference and also at the hotel. I can barely read my email and LWN.