[PATCH v3] tpm: flush timeout work outside buffer_mutex to avoid deadlock

[hyunjungg <hj351016@gmail.com>]

From: Hyunjung Ko <hj351016@gmail.com>

tpm_common_read() calls flush_work(&priv->timeout_work) under
priv->buffer_mutex, but tpm_timeout_work() also takes buffer_mutex, so a
running timeout work deadlocks the flush. Flush after unlocking; the timer
is deleted under the lock, so no new work can be queued.

Fixes: 9488585b21be ("tpm: add support for partial reads")
Cc: stable@vger.kernel.org
Signed-off-by: Hyunjung Ko <hj351016@gmail.com>
---
v3: Trim the commit message to the essentials per Jarkko's review.
    No functional change (same as v2).
 drivers/char/tpm/tpm-dev-common.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/char/tpm/tpm-dev-common.c b/drivers/char/tpm/tpm-dev-common.c
index 6569212..ee91f45 100644
--- a/drivers/char/tpm/tpm-dev-common.c
+++ b/drivers/char/tpm/tpm-dev-common.c
@@ -132,6 +132,7 @@ ssize_t tpm_common_read(struct file *file, char __user *buf,
 {
 	struct file_priv *priv = file->private_data;
 	ssize_t ret_size = 0;
+	bool flush = false;
 	int rc;
 
 	if (!size)
@@ -164,9 +165,18 @@ out:
 	if (!priv->response_length) {
 		*off = 0;
 		timer_delete_sync(&priv->user_read_timer);
-		flush_work(&priv->timeout_work);
+		flush = true;
 	}
 	mutex_unlock(&priv->buffer_mutex);
+
+	/*
+	 * tpm_timeout_work() takes buffer_mutex, so flush it after dropping
+	 * the mutex to avoid a deadlock; the timer is deleted above, so no new
+	 * timeout work can be queued once the mutex is released.
+	 */
+	if (flush)
+		flush_work(&priv->timeout_work);
+
 	return ret_size;
 }
 
-- 
2.43.0