[PATCH v2 1/3] tools: hv: fcopy_daemon: Check buffer limits

["Matej Mužila" <mmuzila@redhat.com>]

From: Matej Mužila <mmuzila@redhat.com>

Check if cpmsg->size is in limits of DATA_FRAGMENT

Signed-off-by: Matej Mužila <mmuzila@redhat.com>
---

If corrupted data are read from /dev/vmbus/hv_fcopy, pwrite can
read from memory outside of the buffer (defined at line 138).
Added check. 

Changes made since v1:
	* max value of cmesg->size is now derived from structure
	  definition in sources/include/uapi/linux/hyperv.h
	* Fixed comments


diff --git a/tools/hv/hv_fcopy_daemon.c b/tools/hv/hv_fcopy_daemon.c
index 6f27e2f..1fc2dc2 100644
--- a/tools/hv/hv_fcopy_daemon.c
+++ b/tools/hv/hv_fcopy_daemon.c
@@ -104,6 +104,10 @@ static int hv_copy_data(struct hv_do_fcopy *cpmsg)
 {
 	ssize_t bytes_written;
 
+	/* Check if the cpmsg->size is in limits of DATA_FRAGMENT */
+	if (cpmsg->size > sizeof(cpmsg->data)) 
+		return HV_E_FAIL;
+
 	bytes_written = pwrite(target_fd, cpmsg->data, cpmsg->size,
 				cpmsg->offset);