linux-kernel - [PATCH 3/4] tpm: in tpm2_del_space check if ops pointer is still valid

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Message-Id: <1610760161-21982-4-git-send-email-LinoSanfilippo@gmx.de>
Date:   Sat, 16 Jan 2021 02:22:40 +0100
From:   Lino Sanfilippo <LinoSanfilippo@....de>
To:     peterhuewe@....de, jarkko@...nel.org
Cc:     jgg@...pe.ca, stefanb@...ux.vnet.ibm.com,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        LinoSanfilippo@....de, p.rosenberger@...bus.com,
        Lino Sanfilippo <l.sanfilippo@...bus.com>
Subject: [PATCH 3/4] tpm: in tpm2_del_space check if ops pointer is still valid

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

In tpm2_del_space() the sessions are flushed by means of the tpm_chip
operations. However the concerning operations pointer my already be NULL at
this time in case that the chip has been unregistered (see
tpm_chip_unregister() which calls tpm_del_char_device() which sets
chip->ops to NULL).
Avoid the NULL pointer access by first calling tpm_try_get_ops() to check
if the operations pointer is still valid and skipping the session flushing
in case of an unregistered chip.

Signed-off-by: Lino Sanfilippo <l.sanfilippo@...bus.com>
---
 drivers/char/tpm/tpm2-space.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/char/tpm/tpm2-space.c b/drivers/char/tpm/tpm2-space.c
index 784b8b3..ea6eee9 100644
--- a/drivers/char/tpm/tpm2-space.c
+++ b/drivers/char/tpm/tpm2-space.c
@@ -59,7 +59,7 @@ 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)) {
+	if (!tpm_try_get_ops(chip) && !tpm_chip_start(chip)) {
 		tpm2_flush_sessions(chip, space);
 		tpm_chip_stop(chip);
 	}
-- 
2.7.4