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Message-ID: <3953c743ce7e7fc1db26f5b849b53df671b2f221.camel@HansenPartnership.com>
Subject: [PATCH] tpm: use try_get_ops() in tpm-space.c
From:   James Bottomley <James.Bottomley@HansenPartnership.com>
To:     Jarkko Sakkinen <jarkko@kernel.org>
Cc:     Sergey Temerkhanov <s.temerkhanov@gmail.com>,
        Peter Huewe <peterhuewe@gmx.de>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Jerry Snitselaar <jsnitsel@redhat.com>,
        linux-integrity@vger.kernel.org,
        linux-kernel <linux-kernel@vger.kernel.org>
Date:   Mon, 07 Mar 2022 15:58:03 -0500
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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.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
---
 drivers/char/tpm/tpm2-space.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/char/tpm/tpm2-space.c b/drivers/char/tpm/tpm2-space.c
index 265ec72b1d81..ffb35f0154c1 100644
--- 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);
 }
-- 
2.34.1