linux-kernel - [PATCH 3/3] tpm: make locality request return value consistent

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Message-Id: <20240131170824.6183-4-dpsmith@apertussolutions.com>
Date: Wed, 31 Jan 2024 12:08:23 -0500
From: "Daniel P. Smith" <dpsmith@...rtussolutions.com>
To: Jason Gunthorpe <jgg@...pe.ca>,
	linux-integrity@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: "Daniel P. Smith" <dpsmith@...rtussolutions.com>,
	Ross Philipson <ross.philipson@...cle.com>,
	Peter Huewe <peterhuewe@....de>,
	Jarkko Sakkinen <jarkko@...nel.org>
Subject: [PATCH 3/3] tpm: make locality request return value consistent

The function tpm_tis_request_locality() is expected to return the locality
value that was requested, or a negative error code upon failure. If it is called
while locality_count of struct tis_data is non-zero, no actual locality request
will be sent. Because the ret variable is initially set to 0, the
locality_count will still get increased, and the function will return 0. For a
caller, this would indicate that locality 0 was successfully requested and not
the state changes just mentioned.

Additionally, the function __tpm_tis_request_locality() provides inconsistent
error codes. It will provide either a failed IO write or a -1 should it have
timed out waiting for locality request to succeed.

This commit changes __tpm_tis_request_locality() to return valid negative error
codes to reflect the reason it fails. It then adjusts the return value check in
tpm_tis_request_locality() to check for a non-negative return value before
incrementing locality_cout. In addition, the initial value of the ret value is
set to a negative error to ensure the check does not pass if
__tpm_tis_request_locality() is not called.

Signed-off-by: Daniel P. Smith <dpsmith@...rtussolutions.com>
Signed-off-by: Ross Philipson <ross.philipson@...cle.com>
---
 drivers/char/tpm/tpm_tis_core.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
index 5709f87991d9..352fefc07823 100644
--- a/drivers/char/tpm/tpm_tis_core.c
+++ b/drivers/char/tpm/tpm_tis_core.c
@@ -208,7 +208,7 @@ static int __tpm_tis_request_locality(struct tpm_chip *chip, int l)
 again:
 		timeout = stop - jiffies;
 		if ((long)timeout <= 0)
-			return -1;
+			return -EBUSY;
 		rc = wait_event_interruptible_timeout(priv->int_queue,
 						      (check_locality
 						       (chip, l)),
@@ -227,18 +227,21 @@ static int __tpm_tis_request_locality(struct tpm_chip *chip, int l)
 			tpm_msleep(TPM_TIMEOUT);
 		} while (time_before(jiffies, stop));
 	}
-	return -1;
+	return -EBUSY;
 }

 static int tpm_tis_request_locality(struct tpm_chip *chip, int l)
 {
 	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
-	int ret = 0;
+	int ret = -EBUSY;
+
+	if (l < 0 || l > TPM_MAX_LOCALITY)
+		return -EINVAL;

 	mutex_lock(&priv->locality_count_mutex);
 	if (priv->locality_count == 0)
 		ret = __tpm_tis_request_locality(chip, l);
-	if (!ret)
+	if (ret >= 0)
 		priv->locality_count++;
 	mutex_unlock(&priv->locality_count_mutex);
 	return ret;
-- 
2.30.2