Xen-netback: Fix issue caused by using gso_type wrongly

Current netback uses gso_type to check whether the skb contains
gso offload, and this is wrong. Gso_size is the right one to
check gso existence, and gso_type is only used to check gso type.

Some skbs contains nonzero gso_type and zero gso_size, current
netback would treat these skbs as gso and create wrong response
for this. This also causes ssh failure to domu from other server.

V2: use skb_is_gso function as Paul Durrant suggested
Signed-off-by: Annie Li <annie.li@oracle.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/xen-netback/netback.c

@@ -240,7 +240,7 @@ static void xenvif_gop_frag_copy(struct xenvif *vif, struct sk_buff *skb,
 	struct gnttab_copy *copy_gop;
 	struct xenvif_rx_meta *meta;
 	unsigned long bytes;
-	int gso_type;
+	int gso_type = XEN_NETIF_GSO_TYPE_NONE;
 
 	/* Data must not cross a page boundary. */
 	BUG_ON(size + offset > PAGE_SIZE<<compound_order(page));
@@ -299,12 +299,12 @@ static void xenvif_gop_frag_copy(struct xenvif *vif, struct sk_buff *skb,
 		}
 
 		/* Leave a gap for the GSO descriptor. */
+		if (skb_is_gso(skb)) {
 			if (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4)
 				gso_type = XEN_NETIF_GSO_TYPE_TCPV4;
 			else if (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6)
 				gso_type = XEN_NETIF_GSO_TYPE_TCPV6;
-		else
-			gso_type = XEN_NETIF_GSO_TYPE_NONE;
+		}
 
 		if (*head && ((1 << gso_type) & vif->gso_mask))
 			vif->rx.req_cons++;
@@ -338,19 +338,15 @@ static int xenvif_gop_skb(struct sk_buff *skb,
 	int head = 1;
 	int old_meta_prod;
 	int gso_type;
-	int gso_size;
 
 	old_meta_prod = npo->meta_prod;
 
-	if (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4) {
+	gso_type = XEN_NETIF_GSO_TYPE_NONE;
+	if (skb_is_gso(skb)) {
+		if (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4)
 			gso_type = XEN_NETIF_GSO_TYPE_TCPV4;
-		gso_size = skb_shinfo(skb)->gso_size;
-	} else if (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6) {
+		else if (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6)
 			gso_type = XEN_NETIF_GSO_TYPE_TCPV6;
-		gso_size = skb_shinfo(skb)->gso_size;
-	} else {
-		gso_type = XEN_NETIF_GSO_TYPE_NONE;
-		gso_size = 0;
 	}
 
 	/* Set up a GSO prefix descriptor, if necessary */
@@ -358,7 +354,7 @@ static int xenvif_gop_skb(struct sk_buff *skb,
 		req = RING_GET_REQUEST(&vif->rx, vif->rx.req_cons++);
 		meta = npo->meta + npo->meta_prod++;
 		meta->gso_type = gso_type;
-		meta->gso_size = gso_size;
+		meta->gso_size = skb_shinfo(skb)->gso_size;
 		meta->size = 0;
 		meta->id = req->id;
 	}
@@ -368,7 +364,7 @@ static int xenvif_gop_skb(struct sk_buff *skb,
 
 	if ((1 << gso_type) & vif->gso_mask) {
 		meta->gso_type = gso_type;
-		meta->gso_size = gso_size;
+		meta->gso_size = skb_shinfo(skb)->gso_size;
 	} else {
 		meta->gso_type = XEN_NETIF_GSO_TYPE_NONE;
 		meta->gso_size = 0;
@@ -500,8 +496,9 @@ static void xenvif_rx_action(struct xenvif *vif)
 			size = skb_frag_size(&skb_shinfo(skb)->frags[i]);
 			max_slots_needed += DIV_ROUND_UP(size, PAGE_SIZE);
 		}
-		if (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4 ||
-		    skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6)
+		if (skb_is_gso(skb) &&
+		   (skb_shinfo(skb)->gso_type & SKB_GSO_TCPV4 ||
+		    skb_shinfo(skb)->gso_type & SKB_GSO_TCPV6))
 			max_slots_needed++;
 
 		/* If the skb may not fit then bail out now */