Theoretically tap_read_packet() may return size less than
s->host_vnet_hdr_len, and next, we'll work with negative size
(in case of !s->using_vnet_hdr). Let's avoid it.

Don't proceed with size == s->host_vnet_hdr_len as well in case
of !s->using_vnet_hdr, it doesn't make sense.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
---

v2: change "<" -> "<="

 net/tap.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/tap.c b/net/tap.c
index 23536c09b46..2a859360193 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -190,6 +190,11 @@ static void tap_send(void *opaque)
             break;
         }

+        if (s->host_vnet_hdr_len && size <= s->host_vnet_hdr_len) {
+            /* Invalid packet */
+            break;
+        }
+
         if (s->host_vnet_hdr_len && !s->using_vnet_hdr) {
             buf  += s->host_vnet_hdr_len;
             size -= s->host_vnet_hdr_len;
--
2.48.1