linux-kernel - [PATCH] mailbox: mailbox-test: fix a locking issue in mbox_test_message

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Date:   Fri, 5 May 2023 12:22:09 +0300
From:   Dan Carpenter <dan.carpenter@...aro.org>
To:     Lee Jones <lee@...nel.org>
Cc:     Jassi Brar <jassisinghbrar@...il.com>,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: [PATCH] mailbox: mailbox-test: fix a locking issue in
 mbox_test_message_write()

There was a bug where this code forgot to unlock the tdev->mutex if the
kzalloc() failed.  Fix this issue, by moving the allocation outside the
lock.

Fixes: 2d1e952a2b8e ("mailbox: mailbox-test: Fix potential double-free in mbox_test_message_write()")
Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
---
 drivers/mailbox/mailbox-test.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/mailbox/mailbox-test.c b/drivers/mailbox/mailbox-test.c
index c4a705c30331..fc6a12a51b40 100644
--- a/drivers/mailbox/mailbox-test.c
+++ b/drivers/mailbox/mailbox-test.c
@@ -98,6 +98,7 @@ static ssize_t mbox_test_message_write(struct file *filp,
 				       size_t count, loff_t *ppos)
 {
 	struct mbox_test_device *tdev = filp->private_data;
+	char *message;
 	void *data;
 	int ret;
 
@@ -113,12 +114,13 @@ static ssize_t mbox_test_message_write(struct file *filp,
 		return -EINVAL;
 	}
 
-	mutex_lock(&tdev->mutex);
-
-	tdev->message = kzalloc(MBOX_MAX_MSG_LEN, GFP_KERNEL);
-	if (!tdev->message)
+	message = kzalloc(MBOX_MAX_MSG_LEN, GFP_KERNEL);
+	if (!message)
 		return -ENOMEM;
 
+	mutex_lock(&tdev->mutex);
+
+	tdev->message = message;
 	ret = copy_from_user(tdev->message, userbuf, count);
 	if (ret) {
 		ret = -EFAULT;
-- 
2.39.2