linux-kernel - [PATCH 1/3] tpm: protect against locality counter underflow

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Message-Id: <20240131170824.6183-2-dpsmith@apertussolutions.com>
Date: Wed, 31 Jan 2024 12:08:21 -0500
From: "Daniel P. Smith" <dpsmith@...rtussolutions.com>
To: Jason Gunthorpe <jgg@...pe.ca>,
	Jarkko Sakkinen <jarkko@...nel.org>,
	Sasha Levin <sashal@...nel.org>,
	Lino Sanfilippo <l.sanfilippo@...bus.com>,
	linux-integrity@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: "Daniel P. Smith" <dpsmith@...rtussolutions.com>,
	Ross Philipson <ross.philipson@...cle.com>,
	Kanth Ghatraju <kanth.ghatraju@...cle.com>,
	Peter Huewe <peterhuewe@....de>
Subject: [PATCH 1/3] tpm: protect against locality counter underflow

Commit 933bfc5ad213 introduced the use of a locality counter to control when a
locality request is allowed to be sent to the TPM. In the commit, the counter
is indiscriminately decremented. Thus creating a situation for an integer
underflow of the counter.

Signed-off-by: Daniel P. Smith <dpsmith@...rtussolutions.com>
Signed-off-by: Ross Philipson <ross.philipson@...cle.com>
Reported-by: Kanth Ghatraju <kanth.ghatraju@...cle.com>
Fixes: 933bfc5ad213 ("tpm, tpm: Implement usage counter for locality")
---
 drivers/char/tpm/tpm_tis_core.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
index 1b350412d8a6..4176d3bd1f04 100644
--- a/drivers/char/tpm/tpm_tis_core.c
+++ b/drivers/char/tpm/tpm_tis_core.c
@@ -180,7 +180,8 @@ static int tpm_tis_relinquish_locality(struct tpm_chip *chip, int l)
 	struct tpm_tis_data *priv = dev_get_drvdata(&chip->dev);
 
 	mutex_lock(&priv->locality_count_mutex);
-	priv->locality_count--;
+	if (priv->locality_count > 0)
+		priv->locality_count--;
 	if (priv->locality_count == 0)
 		__tpm_tis_relinquish_locality(priv, l);
 	mutex_unlock(&priv->locality_count_mutex);
-- 
2.30.2