Bluetooth: Add debugfs support for min LE encryption key size

This patch adds a debugfs control to set a different minimum LE
encryption key size. This is useful for testing that implementation of
the encryption key size handling is behaving correctly (e.g. that we
get appropriate 'Encryption Key Size' error responses when necessary).

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

net/bluetooth/smp.c

@@ -84,6 +84,7 @@ struct smp_dev {
 	u8			local_rand[16];
 	bool			debug_key;
 
+	u8			min_key_size;
 	u8			max_key_size;
 
 	struct crypto_blkcipher	*tfm_aes;
@@ -3136,6 +3137,7 @@ static struct l2cap_chan *smp_add_cid(struct hci_dev *hdev, u16 cid)
 
 	smp->tfm_aes = tfm_aes;
 	smp->tfm_cmac = tfm_cmac;
+	smp->min_key_size = SMP_MIN_ENC_KEY_SIZE;
 	smp->max_key_size = SMP_MAX_ENC_KEY_SIZE;
 
 create_chan:
@@ -3259,6 +3261,50 @@ static const struct file_operations force_bredr_smp_fops = {
 	.llseek		= default_llseek,
 };
 
+static ssize_t le_min_key_size_read(struct file *file,
+				     char __user *user_buf,
+				     size_t count, loff_t *ppos)
+{
+	struct hci_dev *hdev = file->private_data;
+	char buf[4];
+
+	snprintf(buf, sizeof(buf), "%2u\n", SMP_DEV(hdev)->min_key_size);
+
+	return simple_read_from_buffer(user_buf, count, ppos, buf, strlen(buf));
+}
+
+static ssize_t le_min_key_size_write(struct file *file,
+				      const char __user *user_buf,
+				      size_t count, loff_t *ppos)
+{
+	struct hci_dev *hdev = file->private_data;
+	char buf[32];
+	size_t buf_size = min(count, (sizeof(buf) - 1));
+	u8 key_size;
+
+	if (copy_from_user(buf, user_buf, buf_size))
+		return -EFAULT;
+
+	buf[buf_size] = '\0';
+
+	sscanf(buf, "%hhu", &key_size);
+
+	if (key_size > SMP_DEV(hdev)->max_key_size ||
+	    key_size < SMP_MIN_ENC_KEY_SIZE)
+		return -EINVAL;
+
+	SMP_DEV(hdev)->min_key_size = key_size;
+
+	return count;
+}
+
+static const struct file_operations le_min_key_size_fops = {
+	.open		= simple_open,
+	.read		= le_min_key_size_read,
+	.write		= le_min_key_size_write,
+	.llseek		= default_llseek,
+};
+
 static ssize_t le_max_key_size_read(struct file *file,
 				     char __user *user_buf,
 				     size_t count, loff_t *ppos)
@@ -3287,7 +3333,8 @@ static ssize_t le_max_key_size_write(struct file *file,
 
 	sscanf(buf, "%hhu", &key_size);
 
-	if (key_size > SMP_MAX_ENC_KEY_SIZE || key_size < SMP_MIN_ENC_KEY_SIZE)
+	if (key_size > SMP_MAX_ENC_KEY_SIZE ||
+	    key_size < SMP_DEV(hdev)->min_key_size)
 		return -EINVAL;
 
 	SMP_DEV(hdev)->max_key_size = key_size;
@@ -3326,6 +3373,8 @@ int smp_register(struct hci_dev *hdev)
 
 	hdev->smp_data = chan;
 
+	debugfs_create_file("le_min_key_size", 0644, hdev->debugfs, hdev,
+			    &le_min_key_size_fops);
 	debugfs_create_file("le_max_key_size", 0644, hdev->debugfs, hdev,
 			    &le_max_key_size_fops);