USB: usblcd doesn't limit memory consumption during write

usblcd currently has no way to limit memory consumption by fast writers.
This is a security problem, as it allows users with write access to this
device to drive the system into oom despite resource limits.
Here's the fix taken from the modern skeleton driver.

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

diff --git a/drivers/usb/misc/usblcd.c b/drivers/usb/misc/usblcd.c
index 887ef95..12bad8a 100644 (file)
--- a/drivers/usb/misc/usblcd.c
+++ b/drivers/usb/misc/usblcd.c
@@ -42,10 +42,14 @@ struct usb_lcd {
        size_t                  bulk_in_size;           /* the size of the receive buffer */
        __u8                    bulk_in_endpointAddr;   /* the address of the bulk in endpoint */
        __u8                    bulk_out_endpointAddr;  /* the address of the bulk out endpoint */
-       struct kref             kref;
+       struct kref             kref;
+       struct semaphore        limit_sem;              /* to stop writes at full throttle from
+                                                        * using up all RAM */
 };
 #define to_lcd_dev(d) container_of(d, struct usb_lcd, kref)
 
+#define USB_LCD_CONCURRENT_WRITES      5
+
 static struct usb_driver lcd_driver;
 static DEFINE_MUTEX(usb_lcd_open_mutex);
 
@@ -186,12 +190,13 @@ static void lcd_write_bulk_callback(struct urb *urb)
        /* 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 lcd_write(struct file *file, const char __user * user_buffer, size_t count, loff_t *ppos)
 {
        struct usb_lcd *dev;
-        int retval = 0;
+        int retval = 0, r;
        struct urb *urb = NULL;
        char *buf = NULL;
        
@@ -201,10 +206,16 @@ static ssize_t lcd_write(struct file *file, const char __user * user_buffer, siz
        if (count == 0)
                goto exit;
 
+       r = down_interruptible(&dev->limit_sem);
+       if (r < 0)
+               return -EINTR;
+
        /* create a urb, and a buffer for it, and copy the data to the urb */
        urb = usb_alloc_urb(0, GFP_KERNEL);
-       if (!urb)
-               return -ENOMEM;
+       if (!urb) {
+               retval = -ENOMEM;
+               goto err_no_buf;
+       }
        
        buf = usb_buffer_alloc(dev->udev, count, GFP_KERNEL, &urb->transfer_dma);
        if (!buf) {
@@ -239,6 +250,8 @@ exit:
 error:
        usb_buffer_free(dev->udev, count, buf, urb->transfer_dma);
        usb_free_urb(urb);
+err_no_buf:
+       up(&dev->limit_sem);
        return retval;
 }
 
@@ -277,6 +290,7 @@ static int lcd_probe(struct usb_interface *interface, const struct usb_device_id
                goto error;
        }
        kref_init(&dev->kref);
+       sema_init(&dev->limit_sem, USB_LCD_CONCURRENT_WRITES);
 
        dev->udev = usb_get_dev(interface_to_usbdev(interface));
        dev->interface = interface;