tpm: use try_get_ops() in tpm-space.c

commit fb5abce6b2bb5cb3d628aaa63fa821da8c4600f9 upstream.

As part of the series conversion to remove nested TPM operations:

https://lore.kernel.org/all/20190205224723.19671-1-jarkko.sakkinen@linux.intel.com/

exposure of the chip->tpm_mutex was removed from much of the upper
level code.  In this conversion, tpm2_del_space() was missed.  This
didn't matter much because it's usually called closely after a
converted operation, so there's only a very tiny race window where the
chip can be removed before the space flushing is done which causes a
NULL deref on the mutex.  However, there are reports of this window
being hit in practice, so fix this by converting tpm2_del_space() to
use tpm_try_get_ops(), which performs all the teardown checks before
acquring the mutex.

Cc: stable@vger.kernel.org # 5.4.x
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/char/tpm/tpm2-space.c b/drivers/char/tpm/tpm2-space.c
index 97e9168..d222502 100644 (file)
--- a/drivers/char/tpm/tpm2-space.c
+++ b/drivers/char/tpm/tpm2-space.c
@@ -58,12 +58,12 @@ 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) == 0) {
                tpm2_flush_sessions(chip, space);
-               tpm_chip_stop(chip);
+               tpm_put_ops(chip);
        }
-       mutex_unlock(&chip->tpm_mutex);
+
        kfree(space->context_buf);
        kfree(space->session_buf);
 }