[PATCH v3 1/1] crypto: atmel-sha204a - fix heap info leak on I2C transfer failure

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

The nonblocking RNG path allocates a work_data structure to track the
state of an in-flight asynchronous I2C request. This pointer is stored
in rng->priv and later consumed by the read path once the transaction
completes.

If the underlying I2C transfer fails, the completion callback is invoked
with a non-zero status. In this case, the allocated work_data is not
usable for producing RNG output and must not remain associated with the
hwrng state.

Previously, the failure path only logged a warning but left the pointer
state uncleared, which can result in subsequent read attempts observing
stale state and interpreting it as valid completion data.

Fix this by freeing the pending work_data. The I2C transaction reports
an error. This ensures that failed requests do not leave residual state
behind that could be interpreted as valid RNG data on later reads.
Clearing rng->priv is done at the subsequent call to nonblocking read.

Fixes: da001fb651b0 ("crypto: atmel-i2c - add support for SHA204A random number generator")
Signed-off-by: Lothar Rubusch <l.rubusch@gmail.com>
Assisted-by: Gemini:1.5 Pro [google]
Reviewed-by: Thorsten Blum <thorsten.blum@linux.dev>
---
v2 -> v3:
- remove existing error-path cleanup behavior [`rng->priv = 0;`],
  update commit msg
- rebased

v1 -> v2:
- reword commit message for clarity and precision
- keep existing error-path cleanup behavior unchanged, update commit msg

 drivers/crypto/atmel-sha204a.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/crypto/atmel-sha204a.c b/drivers/crypto/atmel-sha204a.c
index 4c9af737b33a..5eb76245347d 100644
--- a/drivers/crypto/atmel-sha204a.c
+++ b/drivers/crypto/atmel-sha204a.c
@@ -31,10 +31,14 @@ 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);
+		atomic_dec(&i2c_priv->tfm_count);
+		return;
+	}
 
 	rng->priv = (unsigned long)work_data;
 	atomic_dec(&i2c_priv->tfm_count);

base-commit: 6ea0ce3a19f9c37a014099e2b0a46b27fa164564
-- 
2.53.0