linux-kernel - [PATCH 5.15 673/846] tpm: fix potential NULL pointer access in tpm_del_char

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Date:   Mon, 24 Jan 2022 19:43:10 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Lino Sanfilippo <LinoSanfilippo@....de>,
        Stefan Berger <stefanb@...ux.ibm.com>,
        Jarkko Sakkinen <jarkko@...nel.org>
Subject: [PATCH 5.15 673/846] tpm: fix potential NULL pointer access in tpm_del_char_device

From: Lino Sanfilippo <LinoSanfilippo@....de>

commit eabad7ba2c752392ae50f24a795093fb115b686d upstream.

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@...r.kernel.org
Signed-off-by: Lino Sanfilippo <LinoSanfilippo@....de>
Fixes: 39d0099f9439 ("powerpc/pseries: Add shutdown() to vio_driver and vio_bus")
Reviewed-by: Stefan Berger <stefanb@...ux.ibm.com>
Tested-by: Stefan Berger <stefanb@...ux.ibm.com>
Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/char/tpm/tpm-chip.c |   18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

--- 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 t
 
 	/* 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);
 }