linux-kernel - [PATCH] w1: Use kfree_sensitive to clear sensitive information

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Date:   Fri, 23 Dec 2022 04:09:22 +0530
From:   Deepak R Varma <drv@...lo.com>
To:     Evgeniy Polyakov <zbr@...emap.net>, linux-kernel@...r.kernel.org
Cc:     Saurabh Singh Sengar <ssengar@...rosoft.com>,
        Praveen Kumar <kumarpraveen@...ux.microsoft.com>, drv@...lo.com
Subject: [PATCH] w1: Use kfree_sensitive to clear sensitive information

Replace combination of 'memset(0) + kfree()' by kfree_sensitive() as it
prevents compiler from optimizing away from zeroing out memory at the
end of a scope. kfree_sensitive() is also safe in case the memory
pointer turns out to be null, which simply gets ignored.

Issue identified using kfree_sensitive.cocci coccinelle semantic patch.

Signed-off-by: Deepak R Varma <drv@...lo.com>
---
Note: proposed change is compile tested only.

 drivers/w1/w1.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/w1/w1.c b/drivers/w1/w1.c
index f2ae2e563dc5..e08467e08b73 100644
--- a/drivers/w1/w1.c
+++ b/drivers/w1/w1.c
@@ -73,8 +73,7 @@ static void w1_master_release(struct device *dev)
 	struct w1_master *md = dev_to_w1_master(dev);

 	dev_dbg(dev, "%s: Releasing %s.\n", __func__, md->name);
-	memset(md, 0, sizeof(struct w1_master) + sizeof(struct w1_bus_master));
-	kfree(md);
+	kfree_sensitive(md);
 }

 static void w1_slave_release(struct device *dev)
@@ -805,9 +804,10 @@ int w1_unref_slave(struct w1_slave *sl)
 		w1_family_notify(BUS_NOTIFY_DEL_DEVICE, sl);
 		device_unregister(&sl->dev);
 		#ifdef DEBUG
-		memset(sl, 0, sizeof(*sl));
-		#endif
+		kfree_sensitive(sl);
+		#else
 		kfree(sl);
+		#endif
 	}
 	atomic_dec(&dev->refcnt);
 	mutex_unlock(&dev->list_mutex);
--
2.34.1