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

fb5abce6 · James Bottomley <[email protected]> · 2022-03-07 15:58:03 -05:00

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

https://lore.kernel.org/all/[email protected]/

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: [email protected] # 5.4.x
Signed-off-by: James Bottomley <[email protected]>
Reviewed-by: Jarkko Sakkinen <[email protected]>
Signed-off-by: Jarkko Sakkinen <[email protected]>

Commit: fb5abce6b2bb5cb3d628aaa63fa821da8c4600f9
Parents: 590bfb57

Changes

1 files changed · +4 −4

File	Status	Add	Del	Content
drivers/char/tpm/tpm2-space.c	modified	+4	−4	View file

drivers/char/tpm/tpm2-space.c

View file

diff --git a/drivers/char/tpm/tpm2-space.c b/drivers/char/tpm/tpm2-space.c
index 265ec72..ffb35f0 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);
 }