[PATCH net v5 3/4] ipmr: set up GSO state for tunnel vifs

[Julius Bairaktaris <julius@bairaktaris.de>]

ip_encap() pushes the outer IPv4 header but does not set SKB_GSO_IPXIP4,
skb->encapsulation or the inner headers. A GSO packet forwarded to a
VIFF_TUNNEL vif is then rejected by ipip_gso_segment() and dropped in
validate_xmit_skb(), after being counted as sent. A device with UDP
segmentation offload is handed a GSO packet whose transport header
points at the inner IP header.

Call iptunnel_handle_offloads() and skb_set_inner_ipproto() as
ipip_tunnel_xmit() does, reserve one outer IP ID per segment as
iptunnel_xmit() does, and set the outer length with iph_set_totlen(),
since a GSO packet plus the outer header can exceed 64 KB. A GSO packet
that GRE or UDP tunnel GRO marked as encapsulated already uses the inner
headers for its own tunnel; drop it before the vif counts it, as
segmentation dropped it before.

Fixes: 9fd1ff5d2ac7 ("udp: Support UDP fraglist GRO/GSO.")
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Julius Bairaktaris <julius@bairaktaris.de>
---
 net/ipv4/ipmr.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 836f3f95b20c4..09d6b0ff1ffb7 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -1869,6 +1869,10 @@ static void ip_encap(struct net *net, struct sk_buff *skb,
 	struct iphdr *iph;
 	const struct iphdr *old_iph = ip_hdr(skb);
 
+	/* skb_cow() in ipmr_prepare_xmit() leaves no header to unclone */
+	iptunnel_handle_offloads(skb, SKB_GSO_IPXIP4);
+	skb_set_inner_ipproto(skb, IPPROTO_IPIP);
+
 	skb_push(skb, sizeof(struct iphdr));
 	skb->transport_header = skb->network_header;
 	skb_reset_network_header(skb);
@@ -1882,8 +1886,8 @@ static void ip_encap(struct net *net, struct sk_buff *skb,
 	iph->saddr	=	saddr;
 	iph->protocol	=	IPPROTO_IPIP;
 	iph->ihl	=	5;
-	iph->tot_len	=	htons(skb->len);
-	ip_select_ident(net, skb, NULL);
+	iph_set_totlen(iph, skb->len);
+	ip_select_ident_segs(net, skb, NULL, skb_shinfo(skb)->gso_segs ?: 1);
 	ip_send_check(iph);
 
 	memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt));
@@ -1951,6 +1955,9 @@ static int ipmr_prepare_xmit(struct net *net, struct mr_table *mrt,
 	}
 
 	if (vif->flags & VIFF_TUNNEL) {
+		/* The inner headers can describe one tunnel only */
+		if (skb_is_gso(skb) && skb->encapsulation)
+			return -1;
 		rt = ip_route_output_ports(net, &fl4, NULL,
 					   vif->remote, vif->local,
 					   0, 0,
-- 
2.53.0