Re: [PATCH net-next v3 1/2] nfc: Add a virtual nci device driver

On Sat, 23 Jan 2021 18:24:24 +0900 Bongsu Jeon wrote:

From: Bongsu Jeon bongsu.jeon@samsung.com

NCI virtual device simulates a NCI device to the user. It can be used to validate the NCI module and applications. This driver supports communication between the virtual NCI device and NCI module.

Signed-off-by: Bongsu Jeon bongsu.jeon@samsung.com

+static bool virtual_ncidev_check_enabled(void) +{

• bool ret = true;
• mutex_lock(&nci_mutex);
• if (state != virtual_ncidev_enabled)

• ret = false;
  

• mutex_unlock(&nci_mutex);
• return ret;

This can be simplified like:

bool ret;

mutex_lock() ret = state == virtual_ncidev_enabled; mutex_unlock()

return ret;

+}

+static int virtual_nci_open(struct nci_dev *ndev) +{

• return 0;

+}

+static int virtual_nci_close(struct nci_dev *ndev) +{

• mutex_lock(&nci_mutex);
• if (send_buff)

• kfree_skb(send_buff);
  

kfree_skb() handles NULL, no need for the if, you can always call kfree_skb() here

• send_buff = NULL;
• mutex_unlock(&nci_mutex);
• return 0;

+}

+static int virtual_nci_send(struct nci_dev *ndev, struct sk_buff *skb) +{

• if (virtual_ncidev_check_enabled() == false)

• return 0;
  

Shouldn't you check this _under_ the lock below?

Otherwise there is a small window between check and use of send_buff

• mutex_lock(&nci_mutex);
• if (send_buff) {

• mutex_unlock(&nci_mutex);
  

• return -1;
  

• }
• send_buff = skb_copy(skb, GFP_KERNEL);
• mutex_unlock(&nci_mutex);
• return 0;

+}

+static struct nci_ops virtual_nci_ops = {

• .open = virtual_nci_open,
• .close = virtual_nci_close,
• .send = virtual_nci_send

+};

+static ssize_t virtual_ncidev_read(struct file *file, char __user *buf,

• 		   size_t count, loff_t *ppos)
  

+{

• size_t actual_len;
• mutex_lock(&nci_mutex);
• if (!send_buff) {

• mutex_unlock(&nci_mutex);
  

• return 0;
  

• }
• actual_len = min_t(size_t, count, send_buff->len);
• if (copy_to_user(buf, send_buff->data, actual_len)) {

• mutex_unlock(&nci_mutex);
  

• return -EFAULT;
  

• }
• skb_pull(send_buff, actual_len);
• if (send_buff->len == 0) {

• consume_skb(send_buff);
  

• send_buff = NULL;
  

• }
• mutex_unlock(&nci_mutex);
• return actual_len;

+}

+static ssize_t virtual_ncidev_write(struct file *file,

• 		    const char __user *buf,
  

• 		    size_t count, loff_t *ppos)
  

+{

• struct sk_buff *skb;
• skb = alloc_skb(count, GFP_KERNEL);
• if (!skb)

• return -ENOMEM;
  

• if (copy_from_user(skb_put(skb, count), buf, count)) {

• kfree_skb(skb);
  

• return -EFAULT;
  

• }
• nci_recv_frame(ndev, skb);
• return count;

+}

+static int virtual_ncidev_open(struct inode *inode, struct file *file) +{

• int ret = 0;
• mutex_lock(&nci_mutex);
• if (state != virtual_ncidev_disabled) {

• mutex_unlock(&nci_mutex);
  

• return -EBUSY;
  

• }
• ndev = nci_allocate_device(&virtual_nci_ops, VIRTUAL_NFC_PROTOCOLS,

• 		   0, 0);
  

• if (!ndev) {

• mutex_unlock(&nci_mutex);
  

• return -ENOMEM;
  

• }
• ret = nci_register_device(ndev);
• if (ret < 0) {

• nci_free_device(ndev);
  

• mutex_unlock(&nci_mutex);
  

• return ret;
  

• }
• state = virtual_ncidev_enabled;
• mutex_unlock(&nci_mutex);
• return 0;

+}

+static int virtual_ncidev_close(struct inode *inode, struct file *file) +{

• mutex_lock(&nci_mutex);
• if (state == virtual_ncidev_enabled) {

• state = virtual_ncidev_disabling;
  

• mutex_unlock(&nci_mutex);
  

• nci_unregister_device(ndev);
  

• nci_free_device(ndev);
  

• mutex_lock(&nci_mutex);
  

• }
• state = virtual_ncidev_disabled;
• mutex_unlock(&nci_mutex);
• return 0;

+}

+static long virtual_ncidev_ioctl(struct file *flip, unsigned int cmd,

• 		 unsigned long arg)
  

+{

• if (cmd == IOCTL_GET_NCIDEV_IDX) {

• struct nfc_dev *nfc_dev = ndev->nfc_dev;
  

• void __user *p = (void __user *)arg;
  

• if (copy_to_user(p, &nfc_dev->idx, sizeof(nfc_dev->idx)))
  

• 	return -EFAULT;
  

• } else {

• return -ENOTTY;
  

• }
• return 0;

Please flip the condition and return early. I think I suggested this already:

{ struct nfc_dev *nfc_dev = ndev->nfc_dev; void __user *p = (void __user *)arg;

if (cmd != IOCTL_GET_NCIDEV_IDX) return -ENOTTY;

if (copy_to_user(p, &nfc_dev->idx, sizeof(nfc_dev->idx))) return -EFAULT;

return 0;