cciss: switch to memdup_user_nul()

all we do to buffer is strncmp()...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

drivers/block/cciss.c

@@ -514,14 +514,9 @@ cciss_proc_write(struct file *file, const char __user *buf,
 	if (!buf || length > PAGE_SIZE - 1)
 		return -EINVAL;
 
-	buffer = (char *)__get_free_page(GFP_KERNEL);
-	if (!buffer)
-		return -ENOMEM;
-
-	err = -EFAULT;
-	if (copy_from_user(buffer, buf, length))
-		goto out;
-	buffer[length] = '\0';
+	buffer = memdup_user_nul(buf, length);
+	if (IS_ERR(buffer))
+		return PTR_ERR(buffer);
 
 #ifdef CONFIG_CISS_SCSI_TAPE
 	if (strncmp(ENGAGE_SCSI, buffer, sizeof ENGAGE_SCSI - 1) == 0) {
@@ -537,8 +532,7 @@ cciss_proc_write(struct file *file, const char __user *buf,
 	/* might be nice to have "disengage" too, but it's not
 	   safely possible. (only 1 module use count, lock issues.) */
 
-out:
-	free_page((unsigned long)buffer);
+	kfree(buffer);
 	return err;
 }