From eabad7ba2c752392ae50f24a795093fb115b686d Mon Sep 17 00:00:00 2001

From: Lino Sanfilippo <LinoSanfilippo@gmx.de>

Date: Mon, 20 Dec 2021 16:06:35 +0100

Subject: [PATCH] tpm: fix potential NULL pointer access in tpm_del_char_device

Git-commit: eabad7ba2c752392ae50f24a795093fb115b686d

Patch-mainline: v5.17-rc1

References: git-fixes bsc#1193660 ltc#195634

Some SPI controller drivers unregister the controller in the shutdown

handler (e.g. BCM2835). If such a controller is used with a TPM 2 slave

chip->ops may be accessed when it is already NULL:

At system shutdown the pre-shutdown handler tpm_class_shutdown() shuts down

TPM 2 and sets chip->ops to NULL. Then at SPI controller unregistration

tpm_tis_spi_remove() is called and eventually calls tpm_del_char_device()

which tries to shut down TPM 2 again. Thereby it accesses chip->ops again:

(tpm_del_char_device calls tpm_chip_start which calls tpm_clk_enable which

calls chip->ops->clk_enable).

Avoid the NULL pointer access by testing if chip->ops is valid and skipping

the TPM 2 shutdown procedure in case it is NULL.

Cc: stable@vger.kernel.org

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>

Fixes: 39d0099f9439 ("powerpc/pseries: Add shutdown() to vio_driver and vio_bus")

Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>

Tested-by: Stefan Berger <stefanb@linux.ibm.com>

Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

Acked-by: Takashi Iwai <tiwai@suse.de>

---

 drivers/char/tpm/tpm-chip.c | 18 +++++++++++++-----

 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c

index b4ed3ae67a4b..b009e7479b70 100644

--- a/drivers/char/tpm/tpm-chip.c

+++ b/drivers/char/tpm/tpm-chip.c

@@ -474,13 +474,21 @@ static void tpm_del_char_device(struct tpm_chip *chip)

 	/* Make the driver uncallable. */

 	down_write(&chip->ops_sem);

-	if (chip->flags & TPM_CHIP_FLAG_TPM2) {

-		if (!tpm_chip_start(chip)) {

-			tpm2_shutdown(chip, TPM2_SU_CLEAR);

-			tpm_chip_stop(chip);

+

+	/*

+	 * Check if chip->ops is still valid: In case that the controller

+	 * drivers shutdown handler unregisters the controller in its

+	 * shutdown handler we are called twice and chip->ops to NULL.

+	 */

+	if (chip->ops) {

+		if (chip->flags & TPM_CHIP_FLAG_TPM2) {

+			if (!tpm_chip_start(chip)) {

+				tpm2_shutdown(chip, TPM2_SU_CLEAR);

+				tpm_chip_stop(chip);

+			}

 		}

+		chip->ops = NULL;

 	}

-	chip->ops = NULL;

 	up_write(&chip->ops_sem);

 }

-- 

2.31.1