[PATCH v3 1/3] crypto: atmel-sha204a - fix memory leak at non-blocking RNG work_data

[Lothar Rubusch <l.rubusch@gmail.com>]

The driver allocated memory for work_data in the non-blocking read
path but never free'd it again. After first read-out the memory pointer
seemed to be recycled and never was allocated again, due to some errors
in the logic, so that the leak was not growing.

Add kfree(work_data) in the completion callback on error. then add
kfree(work_data) after the data is consumed in the subsequent read
call. Finally ensure atomic_dec() is called only after the data has
been consumed or an error occurred to prevent race conditions.

Fixes: da001fb651b0 ("crypto: atmel-i2c - add support for SHA204A random number generator")
Signed-off-by: Lothar Rubusch <l.rubusch@gmail.com>
---
 drivers/crypto/atmel-sha204a.c | 43 ++++++++++++++++++++--------------
 1 file changed, 26 insertions(+), 17 deletions(-)

diff --git a/drivers/crypto/atmel-sha204a.c b/drivers/crypto/atmel-sha204a.c
index dbb39ed0cea1..19720bdd446d 100644
--- a/drivers/crypto/atmel-sha204a.c
+++ b/drivers/crypto/atmel-sha204a.c
@@ -25,13 +25,17 @@ static void atmel_sha204a_rng_done(struct atmel_i2c_work_data *work_data,
 	struct atmel_i2c_client_priv *i2c_priv = work_data->ctx;
 	struct hwrng *rng = areq;
 
-	if (status)
+	if (status) {
 		dev_warn_ratelimited(&i2c_priv->client->dev,
 				     "i2c transaction failed (%d)\n",
 				     status);
+		kfree(work_data);
+		rng->priv = 0;
+		atomic_dec(&i2c_priv->tfm_count);
+		return;
+	}
 
 	rng->priv = (unsigned long)work_data;
-	atomic_dec(&i2c_priv->tfm_count);
 }
 
 static int atmel_sha204a_rng_read_nonblocking(struct hwrng *rng, void *data,
@@ -42,31 +46,36 @@ static int atmel_sha204a_rng_read_nonblocking(struct hwrng *rng, void *data,
 
 	i2c_priv = container_of(rng, struct atmel_i2c_client_priv, hwrng);
 
-	/* keep maximum 1 asynchronous read in flight at any time */
-	if (!atomic_add_unless(&i2c_priv->tfm_count, 1, 1))
-		return 0;
-
+	/* Verify if data available from last run */
 	if (rng->priv) {
 		work_data = (struct atmel_i2c_work_data *)rng->priv;
 		max = min(sizeof(work_data->cmd.data), max);
 		memcpy(data, &work_data->cmd.data, max);
-		rng->priv = 0;
-	} else {
-		work_data = kmalloc_obj(*work_data, GFP_ATOMIC);
-		if (!work_data) {
-			atomic_dec(&i2c_priv->tfm_count);
-			return -ENOMEM;
-		}
-		work_data->ctx = i2c_priv;
-		work_data->client = i2c_priv->client;
 
-		max = 0;
+		/* Now, free memory */
+		kfree(work_data);
+		rng->priv = 0;
+		atomic_dec(&i2c_priv->tfm_count);
+		return max;
 	}
 
+	/* When a request is still in-flight but not processed */
+	if (atomic_read(&i2c_priv->tfm_count) > 0)
+		return 0;
+
+	/* Start a new request */
+	work_data = kmalloc_obj(*work_data, GFP_ATOMIC);
+	if (!work_data)
+		return -ENOMEM;
+
+	atomic_inc(&i2c_priv->tfm_count);
+	work_data->ctx = i2c_priv;
+	work_data->client = i2c_priv->client;
+
 	atmel_i2c_init_random_cmd(&work_data->cmd);
 	atmel_i2c_enqueue(work_data, atmel_sha204a_rng_done, rng);
 
-	return max;
+	return 0;
 }
 
 static int atmel_sha204a_rng_read(struct hwrng *rng, void *data, size_t max,
-- 
2.53.0