linux-kernel - [PATCH 5.16 34/37] tpm: use try_get

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Date:   Fri, 25 Mar 2022 16:14:44 +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,
        James Bottomley <James.Bottomley@...senPartnership.com>,
        Jarkko Sakkinen <jarkko@...nel.org>
Subject: [PATCH 5.16 34/37] tpm: use try_get_ops() in tpm-space.c

From: James Bottomley <James.Bottomley@...senPartnership.com>

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@...r.kernel.org # 5.4.x
Signed-off-by: James Bottomley <James.Bottomley@...senPartnership.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/tpm2-space.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- 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 *sp

 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);
 }