[media] dvb_frontend: Use memdup_user() rather than duplicating its implementation

* Reuse existing functionality from memdup_user() instead of keeping
  duplicate source code.

  This issue was detected by using the Coccinelle software.

* Return directly if this copy operation failed.

* Replace the specification of data structures by pointer dereferences
  to make the corresponding size determination a bit safer according to
  the Linux coding style convention.
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

drivers/media/dvb-core/dvb_frontend.c

@@ -1969,17 +1969,9 @@ static int dvb_frontend_ioctl_properties(struct file *file,
 		if ((tvps->num == 0) || (tvps->num > DTV_IOCTL_MAX_MSGS))
 			return -EINVAL;
 
-		tvp = kmalloc(tvps->num * sizeof(struct dtv_property), GFP_KERNEL);
-		if (!tvp) {
-			err = -ENOMEM;
-			goto out;
-		}
-
-		if (copy_from_user(tvp, (void __user *)tvps->props,
-				   tvps->num * sizeof(struct dtv_property))) {
-			err = -EFAULT;
-			goto out;
-		}
+		tvp = memdup_user(tvps->props, tvps->num * sizeof(*tvp));
+		if (IS_ERR(tvp))
+			return PTR_ERR(tvp);
 
 		for (i = 0; i < tvps->num; i++) {
 			err = dtv_property_process_set(fe, tvp + i, file);
@@ -2002,17 +1994,9 @@ static int dvb_frontend_ioctl_properties(struct file *file,
 		if ((tvps->num == 0) || (tvps->num > DTV_IOCTL_MAX_MSGS))
 			return -EINVAL;
 
-		tvp = kmalloc(tvps->num * sizeof(struct dtv_property), GFP_KERNEL);
-		if (!tvp) {
-			err = -ENOMEM;
-			goto out;
-		}
-
-		if (copy_from_user(tvp, (void __user *)tvps->props,
-				   tvps->num * sizeof(struct dtv_property))) {
-			err = -EFAULT;
-			goto out;
-		}
+		tvp = memdup_user(tvps->props, tvps->num * sizeof(*tvp));
+		if (IS_ERR(tvp))
+			return PTR_ERR(tvp);
 
 		/*
 		 * Let's use our own copy of property cache, in order to