[PATCH v2 11/12] crypto: atmel-sha204a - fix heap info leak on I2C transfer failure

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

When a non-blocking read operation is requested, the driver dynamically
allocates memory to track asynchronous transfer status. If the underlying
I2C transmission fails, atmel_sha204a_rng_done() logs a rate-limited
warning but incorrectly proceeds to cache the pointer to this uninitialized
buffer inside the rng->priv data field anyway.

On subsequent execution passes, atmel_sha204a_rng_read_nonblocking()
detects the stale rng->priv value, skips executing a hardware data read,
and copies up to 32 bytes of uninitialized kernel heap data from this
garbage memory pool straight back into the system's hwrng data stream.

Fix this information disclosure vector by immediately releasing the
allocated asynchronous work data buffer and explicitly clearing the
tracking pointer context whenever an I2C transaction returns a non-zero
error status.

Additionally, ensure that tfm counter is decremented within the error path
to prevent reference counter stagnation, which would otherwise leave the
driver in a permanently busy state. Finding by a sashiko side-review.

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 | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/crypto/atmel-sha204a.c b/drivers/crypto/atmel-sha204a.c
index 38a269186e2a..3d29543032cc 100644
--- a/drivers/crypto/atmel-sha204a.c
+++ b/drivers/crypto/atmel-sha204a.c
@@ -31,10 +31,15 @@ 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);
-- 
2.39.5