[PATCH 2/2] net/virtio: fix fortify memcpy warning

[Stephen Hemminger <stephen@networkplumber.org>]

If fortify is enabled, it will generate a warning if memcpy
src is NULL even if size is zero. This happens if the MP message
sync is called with no file descriptors.

Bugzilla ID 1446
Fixes: 6a84c37e3975 ("net/virtio-user: add vhost-user adapter layer")

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
 drivers/net/virtio/virtio_user/vhost_user.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/virtio/virtio_user/vhost_user.c b/drivers/net/virtio/virtio_user/vhost_user.c
index 3c05ac9cc0..c10252506b 100644
--- a/drivers/net/virtio/virtio_user/vhost_user.c
+++ b/drivers/net/virtio/virtio_user/vhost_user.c
@@ -128,7 +128,8 @@ vhost_user_write(int fd, struct vhost_user_msg *msg, int *fds, int fd_num)
 	cmsg->cmsg_len = CMSG_LEN(fd_size);
 	cmsg->cmsg_level = SOL_SOCKET;
 	cmsg->cmsg_type = SCM_RIGHTS;
-	memcpy(CMSG_DATA(cmsg), fds, fd_size);
+	if (fd_size > 0)
+		memcpy(CMSG_DATA(cmsg), fds, fd_size);
 
 	do {
 		r = sendmsg(fd, &msgh, 0);
-- 
2.43.0