[PATCH v2 02/12] crypto: atmel-ecc - fix use after free situation

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

Fixes the very likely race condition, having multiple of such devices
attached (identified by sashiko feedback).

The Scenario:
    Thread A (Device 1 Probe): Successfully adds i2c_priv to the global
             list (Line 324). The lock is released.
    Thread B (An active crypto request): Concurrently calls
              atmel_ecc_i2c_client_alloc(). It scans the global list, sees
              Device 1, and assigns a crypto job to it.
    Thread A: Moves to line 332. crypto_register_kpp() fails (e.g., out of
              memory or name clash).
    Thread A: Enters the error path. It removes Device 1 from the list and
              frees the i2c_priv memory.
    Thread B: Is still actively trying to talk to the I2C hardware using
              the i2c_priv pointer it grabbed in Step 2. The memory is now
              gone. Result: Kernel crash (Use-After-Free).

Fixes: 11105693fa05 ("crypto: atmel-ecc - introduce Microchip / Atmel ECC driver")
Signed-off-by: Lothar Rubusch <l.rubusch@gmail.com>
---
 drivers/crypto/atmel-ecc.c | 12 ++++++++++++
 drivers/crypto/atmel-i2c.h |  2 ++
 2 files changed, 14 insertions(+)

diff --git a/drivers/crypto/atmel-ecc.c b/drivers/crypto/atmel-ecc.c
index c9f798ebf44f..19d5435aa42b 100644
--- a/drivers/crypto/atmel-ecc.c
+++ b/drivers/crypto/atmel-ecc.c
@@ -218,6 +218,8 @@ static struct i2c_client *atmel_ecc_i2c_client_alloc(void)
 
 	list_for_each_entry(i2c_priv, &atmel_i2c_mgmt.i2c_client_list,
 			    i2c_client_list_node) {
+		if (!i2c_priv->ready)
+			continue;
 		tfm_cnt = atomic_read(&i2c_priv->tfm_count);
 		if (tfm_cnt < min_tfm_cnt) {
 			min_tfm_cnt = tfm_cnt;
@@ -322,6 +324,7 @@ static int atmel_ecc_probe(struct i2c_client *client)
 		return ret;
 
 	i2c_priv = i2c_get_clientdata(client);
+	i2c_priv->ready = false;
 
 	spin_lock(&atmel_i2c_mgmt.i2c_list_lock);
 	list_add_tail(&i2c_priv->i2c_client_list_node,
@@ -336,10 +339,15 @@ static int atmel_ecc_probe(struct i2c_client *client)
 
 		dev_err(&client->dev, "%s alg registration failed\n",
 			atmel_ecdh_nist_p256.base.cra_driver_name);
+		return ret;
 	} else {
 		dev_info(&client->dev, "atmel ecc algorithms registered in /proc/crypto\n");
 	}
 
+	spin_lock(&atmel_i2c_mgmt.i2c_list_lock);
+	i2c_priv->ready = true;
+	spin_unlock(&atmel_i2c_mgmt.i2c_list_lock);
+
 	return ret;
 }
 
@@ -347,6 +355,10 @@ static void atmel_ecc_remove(struct i2c_client *client)
 {
 	struct atmel_i2c_client_priv *i2c_priv = i2c_get_clientdata(client);
 
+	spin_lock(&atmel_i2c_mgmt.i2c_list_lock);
+	i2c_priv->ready = false;
+	spin_unlock(&atmel_i2c_mgmt.i2c_list_lock);
+
 	/* Return EBUSY if i2c client already allocated. */
 	if (atomic_read(&i2c_priv->tfm_count)) {
 		/*
diff --git a/drivers/crypto/atmel-i2c.h b/drivers/crypto/atmel-i2c.h
index 72f04c15682f..e3b12030f9c4 100644
--- a/drivers/crypto/atmel-i2c.h
+++ b/drivers/crypto/atmel-i2c.h
@@ -129,6 +129,7 @@ struct atmel_ecc_driver_data {
  * @wake_token_sz       : size in bytes of the wake_token
  * @tfm_count           : number of active crypto transformations on i2c client
  * @hwrng               : hold the hardware generated rng
+ * @ready               : hw client is ready to use
  *
  * Reads and writes from/to the i2c client are sequential. The first byte
  * transmitted to the device is treated as the byte size. Any attempt to send
@@ -145,6 +146,7 @@ struct atmel_i2c_client_priv {
 	size_t wake_token_sz;
 	atomic_t tfm_count ____cacheline_aligned;
 	struct hwrng hwrng;
+	bool ready;
 };
 
 /**
-- 
2.39.5