[PATCH] net/virtio: do not gso when no header is present

[Emmanuel Roullit <emmanuel.roullit@gmail.com>]

Found with clang static analysis:
lib/librte_vhost/virtio_net.c:723:17: warning:
Access to field 'data_off' results in a dereference of a null pointer
(loaded from variable 'tcp_hdr')
        m->l4_len = (tcp_hdr->data_off & 0xf0) >> 2;
                     ^~~~~~~~~~~~~~~~~

Fixes: 2a51b1091cb5 ("vhost: support indirect descriptor in non-mergeable Rx")

Signed-off-by: Emmanuel Roullit <emmanuel.roullit@gmail.com>
---
 lib/librte_vhost/virtio_net.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
index 595f67c4d..82444b7b9 100644
--- a/lib/librte_vhost/virtio_net.c
+++ b/lib/librte_vhost/virtio_net.c
@@ -677,6 +677,7 @@ parse_ethernet(struct rte_mbuf *m, uint16_t *l4_proto, void **l4_hdr)
 	default:
 		m->l3_len = 0;
 		*l4_proto = 0;
+		*l4_hdr = NULL;
 		break;
 	}
 }
@@ -713,7 +714,7 @@ vhost_dequeue_offload(struct virtio_net_hdr *hdr, struct rte_mbuf *m)
 		}
 	}
 
-	if (hdr->gso_type != VIRTIO_NET_HDR_GSO_NONE) {
+	if (l4_hdr && hdr->gso_type != VIRTIO_NET_HDR_GSO_NONE) {
 		switch (hdr->gso_type & ~VIRTIO_NET_HDR_GSO_ECN) {
 		case VIRTIO_NET_HDR_GSO_TCPV4:
 		case VIRTIO_NET_HDR_GSO_TCPV6:
-- 
2.11.0