[PATCH] crypto: atmel-sha204a - clear RNG data from memory

[Thorsten Blum <thorsten.blum@linux.dev>]

In atmel_sha204a_rng_read(), use memzero_explicit() to clear the local
stack variable cmd before it goes out of scope, since cmd.data may still
hold the last 32 random bytes.

Since atmel_sha204a_rng_done() caches work_data in hwrng::priv, and its
response data is later used as RNG entropy, use kfree_sensitive() to
clear the cached data on transaction failure and device removal.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
---
 drivers/crypto/atmel-sha204a.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/crypto/atmel-sha204a.c b/drivers/crypto/atmel-sha204a.c
index 5eb76245347d..21a84c29c9b7 100644
--- a/drivers/crypto/atmel-sha204a.c
+++ b/drivers/crypto/atmel-sha204a.c
@@ -15,6 +15,7 @@
 #include <linux/module.h>
 #include <linux/scatterlist.h>
 #include <linux/slab.h>
+#include <linux/string.h>
 #include <linux/sysfs.h>
 #include <linux/workqueue.h>
 #include "atmel-i2c.h"
@@ -35,7 +36,7 @@ static void atmel_sha204a_rng_done(struct atmel_i2c_work_data *work_data,
 		dev_warn_ratelimited(&i2c_priv->client->dev,
 				     "i2c transaction failed (%d)\n",
 				     status);
-		kfree(work_data);
+		kfree_sensitive(work_data);
 		atomic_dec(&i2c_priv->tfm_count);
 		return;
 	}
@@ -95,12 +96,15 @@ static int atmel_sha204a_rng_read(struct hwrng *rng, void *data, size_t max,
 
 	ret = atmel_i2c_send_receive(i2c_priv->client, &cmd);
 	if (ret)
-		return ret;
+		goto out;
 
 	max = min(RANDOM_RSP_SIZE - CMD_OVERHEAD_SIZE, max);
 	memcpy(data, &cmd.data[RSP_DATA_IDX], max);
+	ret = max;
 
-	return max;
+out:
+	memzero_explicit(&cmd, sizeof(cmd));
+	return ret;
 }
 
 static int atmel_sha204a_otp_read(struct i2c_client *client, u16 addr, u8 *otp)
@@ -209,7 +213,7 @@ static void atmel_sha204a_remove(struct i2c_client *client)
 	devm_hwrng_unregister(&client->dev, &i2c_priv->hwrng);
 	atmel_i2c_flush_queue();
 
-	kfree((void *)i2c_priv->hwrng.priv);
+	kfree_sensitive((void *)i2c_priv->hwrng.priv);
 }
 
 static const struct of_device_id atmel_sha204a_dt_ids[] = {

base-commit: e264401ce4776a288524e5b87593d4d864147115