[PATCH] USB: Limiting of resource use in skeleton driver

this introduces limits whose lack in the skeleton driver someone recently
complained about.

Signed-off-by: Oliver Neukum <oliver@neukum.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 18 insertions, 7 deletions

diff --git a/drivers/usb/usb-skeleton.c b/drivers/usb/usb-skeleton.c
index 60c458ebaa2d..719d23a4ac51 100644
--- a/drivers/usb/usb-skeleton.c
+++ b/drivers/usb/usb-skeleton.c
@@ -39,10 +39,15 @@ MODULE_DEVICE_TABLE (usb, skel_table);
 /* Get a minor range for your devices from the usb maintainer */
 #define USB_SKEL_MINOR_BASE     192
 
+/* our private defines. if this grows any larger, use your own .h file */
+#define MAX_TRANSFER            ( PAGE_SIZE - 512 )
+#define WRITES_IN_FLIGHT        8
+
 /* Structure to hold all of our device specific stuff */
 struct usb_skel {
         struct usb_device *     udev;                   /* the usb device for this device */
         struct usb_interface *  interface;              /* the interface for this device */
+        struct semaphore        limit_sem;              /* limiting the number of writes in progress */
         unsigned char *         bulk_in_buffer;         /* the buffer to receive data */
         size_t                  bulk_in_size;           /* the size of the receive buffer */
         __u8                    bulk_in_endpointAddr;   /* the address of the bulk in endpoint */
@@ -152,6 +157,7 @@ static void skel_write_bulk_callback(struct urb *urb, struct pt_regs *regs)
         /* free up our allocated buffer */
         usb_buffer_free(urb->dev, urb->transfer_buffer_length, 
                         urb->transfer_buffer, urb->transfer_dma);
+        up(&dev->limit_sem);
 }
 
 static ssize_t skel_write(struct file *file, const char *user_buffer, size_t count, loff_t *ppos)
@@ -160,6 +166,7 @@ static ssize_t skel_write(struct file *file, const char *user_buffer, size_t cou
         int retval = 0;
         struct urb *urb = NULL;
         char *buf = NULL;
+        size_t writesize = max(count, MAX_TRANSFER);
 
         dev = (struct usb_skel *)file->private_data;
 
@@ -167,6 +174,9 @@ static ssize_t skel_write(struct file *file, const char *user_buffer, size_t cou
         if (count == 0)
                 goto exit;
 
+        /* limit the number of URBs in flight to stop a user from using up all RAM */
+        down (&dev->limit_sem);
+
         /* create a urb, and a buffer for it, and copy the data to the urb */
         urb = usb_alloc_urb(0, GFP_KERNEL);
         if (!urb) {
@@ -174,13 +184,13 @@ static ssize_t skel_write(struct file *file, const char *user_buffer, size_t cou
                 goto error;
         }
 
-        buf = usb_buffer_alloc(dev->udev, count, GFP_KERNEL, &urb->transfer_dma);
+        buf = usb_buffer_alloc(dev->udev, writesize, GFP_KERNEL, &urb->transfer_dma);
         if (!buf) {
                 retval = -ENOMEM;
                 goto error;
         }
 
-        if (copy_from_user(buf, user_buffer, count)) {
+        if (copy_from_user(buf, user_buffer, writesize)) {
                 retval = -EFAULT;
                 goto error;
         }
@@ -188,7 +198,7 @@ static ssize_t skel_write(struct file *file, const char *user_buffer, size_t cou
         /* initialize the urb properly */
         usb_fill_bulk_urb(urb, dev->udev,
                           usb_sndbulkpipe(dev->udev, dev->bulk_out_endpointAddr),
-                          buf, count, skel_write_bulk_callback, dev);
+                          buf, writesize, skel_write_bulk_callback, dev);
         urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
 
         /* send the data out the bulk port */
@@ -202,11 +212,12 @@ static ssize_t skel_write(struct file *file, const char *user_buffer, size_t cou
         usb_free_urb(urb);
 
 exit:
-        return count;
+        return writesize;
 
 error:
-        usb_buffer_free(dev->udev, count, buf, urb->transfer_dma);
+        usb_buffer_free(dev->udev, writesize, buf, urb->transfer_dma);
         usb_free_urb(urb);
+        up(&dev->limit_sem);
         return retval;
 }
 
@@ -238,13 +249,13 @@ static int skel_probe(struct usb_interface *interface, const struct usb_device_i
         int retval = -ENOMEM;
 
         /* allocate memory for our device state and initialize it */
-        dev = kmalloc(sizeof(*dev), GFP_KERNEL);
+        dev = kzalloc(sizeof(*dev), GFP_KERNEL);
         if (dev == NULL) {
                 err("Out of memory");
                 goto error;
         }
-        memset(dev, 0x00, sizeof(*dev));
         kref_init(&dev->kref);
+        sema_init(&dev->limit_sem, WRITES_IN_FLIGHT);
 
         dev->udev = usb_get_dev(interface_to_usbdev(interface));
         dev->interface = interface;