linux-kernel - [PATCH v3 2/2] tpm: in tpm2_del_space check if ops pointer is still valid

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Message-Id: <1612482643-11796-3-git-send-email-LinoSanfilippo@gmx.de>
Date:   Fri,  5 Feb 2021 00:50:43 +0100
From:   Lino Sanfilippo <LinoSanfilippo@....de>
To:     peterhuewe@....de, jarkko@...nel.org
Cc:     jgg@...pe.ca, stefanb@...ux.vnet.ibm.com,
        James.Bottomley@...senpartnership.com, stable@...r.kernel.org,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        LinoSanfilippo@....de, Lino Sanfilippo <l.sanfilippo@...bus.com>
Subject: [PATCH v3 2/2] tpm: in tpm2_del_space check if ops pointer is still valid

From: Lino Sanfilippo <l.sanfilippo@...bus.com>

In tpm2_del_space() chip->ops is used for flushing the sessions. However
this function may be called after tpm_chip_unregister() which sets
the chip->ops pointer to NULL.
Avoid a possible NULL pointer dereference by checking if chip->ops is still
valid before accessing it.

Fixes: a3fbfae82b4c ("tpm: take TPM chip power gating out of tpm_transmit()")
Signed-off-by: Lino Sanfilippo <l.sanfilippo@...bus.com>
---
 drivers/char/tpm/tpm2-space.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/char/tpm/tpm2-space.c b/drivers/char/tpm/tpm2-space.c
index 784b8b3..9a29a40 100644
--- a/drivers/char/tpm/tpm2-space.c
+++ b/drivers/char/tpm/tpm2-space.c
@@ -58,12 +58,17 @@ int tpm2_init_space(struct tpm_space *space, unsigned int buf_size)
 
 void tpm2_del_space(struct tpm_chip *chip, struct tpm_space *space)
 {
-	mutex_lock(&chip->tpm_mutex);
-	if (!tpm_chip_start(chip)) {
-		tpm2_flush_sessions(chip, space);
-		tpm_chip_stop(chip);
+	down_read(&chip->ops_sem);
+	if (chip->ops) {
+		mutex_lock(&chip->tpm_mutex);
+		if (!tpm_chip_start(chip)) {
+			tpm2_flush_sessions(chip, space);
+			tpm_chip_stop(chip);
+		}
+		mutex_unlock(&chip->tpm_mutex);
 	}
-	mutex_unlock(&chip->tpm_mutex);
+	up_read(&chip->ops_sem);
+
 	kfree(space->context_buf);
 	kfree(space->session_buf);
 }
-- 
2.7.4