[PATCH v2 03/12] crypto: atmel-ecc - fix multi-device kpp registration

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

In a scenario where multiple such devices are attached, the following
situation may arise (finding by sashiko):

Device 1 Probes:
Calls crypto_register_kpp(&atmel_ecdh_nist_p256). The Crypto Core modifies
fields inside this global structure to link it into the system-wide
algorithm list. Registration succeeds.

Device 2 Probes (Minutes later, on a system with two of these I2C chips):
It executes the exact same line of code. It passes the exact same global
&atmel_ecdh_nist_p256 memory address to crypto_register_kpp().

The Disaster:
The Crypto Core tries to register it again. It overwrites the internal
fields that Device 1 was already using. This corrupts the Linux crypto
subsystem's internal linked lists, usually leading to an immediate kernel
panic or silent memory corruption.

Introduce a global mutex and reference counter to ensure that the static
kpp algorithm is registered only once by the first probing device, and
unregistered only when the last matching device is removed.

Fixes: 11105693fa05 ("crypto: atmel-ecc - introduce Microchip / Atmel ECC driver")
Signed-off-by: Lothar Rubusch <l.rubusch@gmail.com>
---
 drivers/crypto/atmel-ecc.c | 55 +++++++++++++++++++++-----------------
 1 file changed, 30 insertions(+), 25 deletions(-)

diff --git a/drivers/crypto/atmel-ecc.c b/drivers/crypto/atmel-ecc.c
index 19d5435aa42b..e5dd166fd785 100644
--- a/drivers/crypto/atmel-ecc.c
+++ b/drivers/crypto/atmel-ecc.c
@@ -23,6 +23,9 @@
 #include <crypto/kpp.h>
 #include "atmel-i2c.h"
 
+static DEFINE_MUTEX(atmel_ecc_kpp_lock);
+static int atmel_ecc_kpp_refcnt;
+
 static struct atmel_ecc_driver_data atmel_i2c_mgmt;
 
 /**
@@ -331,23 +334,30 @@ static int atmel_ecc_probe(struct i2c_client *client)
 		      &atmel_i2c_mgmt.i2c_client_list);
 	spin_unlock(&atmel_i2c_mgmt.i2c_list_lock);
 
-	ret = crypto_register_kpp(&atmel_ecdh_nist_p256);
-	if (ret) {
-		spin_lock(&atmel_i2c_mgmt.i2c_list_lock);
-		list_del(&i2c_priv->i2c_client_list_node);
-		spin_unlock(&atmel_i2c_mgmt.i2c_list_lock);
+	mutex_lock(&atmel_ecc_kpp_lock);
+	if (atmel_ecc_kpp_refcnt == 0) {
+		ret = crypto_register_kpp(&atmel_ecdh_nist_p256);
+		if (ret) {
+			spin_lock(&atmel_i2c_mgmt.i2c_list_lock);
+			list_del(&i2c_priv->i2c_client_list_node);
+			spin_unlock(&atmel_i2c_mgmt.i2c_list_lock);
 
-		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");
+			dev_err(&client->dev, "%s alg registration failed\n",
+				atmel_ecdh_nist_p256.base.cra_driver_name);
+
+			mutex_unlock(&atmel_ecc_kpp_lock);
+			return ret;
+		}
 	}
+	atmel_ecc_kpp_refcnt++;
+	mutex_unlock(&atmel_ecc_kpp_lock);
 
 	spin_lock(&atmel_i2c_mgmt.i2c_list_lock);
 	i2c_priv->ready = true;
 	spin_unlock(&atmel_i2c_mgmt.i2c_list_lock);
 
+	dev_info(&client->dev, "atmel ecc algorithms registered in /proc/crypto\n");
+
 	return ret;
 }
 
@@ -359,21 +369,16 @@ static void atmel_ecc_remove(struct i2c_client *client)
 	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)) {
-		/*
-		 * After we return here, the memory backing the device is freed.
-		 * That happens no matter what the return value of this function
-		 * is because in the Linux device model there is no error
-		 * handling for unbinding a driver.
-		 * If there is still some action pending, it probably involves
-		 * accessing the freed memory.
-		 */
-		dev_emerg(&client->dev, "Device is busy, expect memory corruption.\n");
-		return;
-	}
-
-	crypto_unregister_kpp(&atmel_ecdh_nist_p256);
+	/*
+	 * Note, the Linux Crypto Core automatically blocks until all active
+	 * transformations utilizing that specific algorithm structure
+	 * are fully freed and closed.
+	 */
+	mutex_lock(&atmel_ecc_kpp_lock);
+	atmel_ecc_kpp_refcnt--;
+	if (atmel_ecc_kpp_refcnt == 0)
+		crypto_unregister_kpp(&atmel_ecdh_nist_p256);
+	mutex_unlock(&atmel_ecc_kpp_lock);
 
 	spin_lock(&atmel_i2c_mgmt.i2c_list_lock);
 	list_del(&i2c_priv->i2c_client_list_node);
-- 
2.39.5