Commit eabad7ba authored Dec 20, 2021 by Lino Sanfilippo Committed by Jarkko Sakkinen Jan 09, 2022

tpm: fix potential NULL pointer access in tpm_del_char_device



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: 39d0099f ("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>

parent 0aa69878

drivers/char/tpm/tpm-chip.c

+13 −5

Original line number	Diff line number	Diff line
		@@ -474,6 +474,13 @@ static void tpm_del_char_device(struct tpm_chip *chip)

		/* Make the driver uncallable. */
		down_write(&chip->ops_sem);

		/*
		* 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);
		@@ -481,6 +488,7 @@ static void tpm_del_char_device(struct tpm_chip *chip)
		}
		}
		chip->ops = NULL;
		}
		up_write(&chip->ops_sem);
		}