[PATCH v9 13/19] tpm: Protect against locality counter underflow

Ross Philipson
2024-05-31T01:33:04Z

From: "Daniel P. Smith" <dpsmith@apertussolutions.com>

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@apertussolutions.com>
Signed-off-by: Ross Philipson <ross.philipson@oracle.com>
Reported-by: Kanth Ghatraju <kanth.ghatraju@oracle.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 176cd8dbf1db..7c1761bd6000 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);
--
2.39.3