linux-kernel - [PATCH] char: xillybus: Fix trivial bug with mutex

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Date:   Thu, 17 Nov 2022 09:18:25 +0200
From:   Eli Billauer <eli.billauer@...il.com>
To:     gregkh@...uxfoundation.org
Cc:     arnd@...db.de, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org, imv4bel@...il.com,
        stern@...land.harvard.edu, Eli Billauer <eli.billauer@...il.com>
Subject: [PATCH] char: xillybus: Fix trivial bug with mutex

@unit_mutex protects @unit from being freed, so obviously it should be
released after @unit is used, and not before.

This is a follow-up to commit 282a4b71816b ("char: xillybus: Prevent
use-after-free due to race condition") which ensures, among others, the
protection of @private_data after @unit_mutex has been released.

Reported-by: Hyunwoo Kim <imv4bel@...il.com>
Signed-off-by: Eli Billauer <eli.billauer@...il.com>
---
 drivers/char/xillybus/xillybus_class.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/char/xillybus/xillybus_class.c b/drivers/char/xillybus/xillybus_class.c
index 0f238648dcfe..e9a288e61c15 100644
--- a/drivers/char/xillybus/xillybus_class.c
+++ b/drivers/char/xillybus/xillybus_class.c
@@ -227,14 +227,15 @@ int xillybus_find_inode(struct inode *inode,
 			break;
 		}
 
-	mutex_unlock(&unit_mutex);
-
-	if (!unit)
+	if (!unit) {
+		mutex_unlock(&unit_mutex);
 		return -ENODEV;
+	}
 
 	*private_data = unit->private_data;
 	*index = minor - unit->lowest_minor;
 
+	mutex_unlock(&unit_mutex);
 	return 0;
 }
 EXPORT_SYMBOL(xillybus_find_inode);
-- 
2.17.1