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: 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>

diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
index b4ed3ae..b009e74 100644 (file)
--- 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);
 }