xfrm: replay: Fix ESN wrap around for GSO

When using GSO it can happen that the wrong seq_hi is used for the last
packets before the wrap around. This can lead to double usage of a
sequence number. To avoid this, we should serialize this last GSO
packet.

Fixes: d7dbefc4 ("xfrm: Add xfrm_replay_overflow functions for offloading")
Co-developed-by: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Christian Langrock <christian.langrock@secunet.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/ipv4/esp4_offload.c

@@ -314,6 +314,9 @@ static int esp_xmit(struct xfrm_state *x, struct sk_buff *skb,  netdev_features_
 			xo->seq.low += skb_shinfo(skb)->gso_segs;
 	}
 
+	if (xo->seq.low < seq)
+		xo->seq.hi++;
+
 	esp.seqno = cpu_to_be64(seq + ((u64)xo->seq.hi << 32));
 
 	ip_hdr(skb)->tot_len = htons(skb->len);

net/ipv6/esp6_offload.c

@@ -346,6 +346,9 @@ static int esp6_xmit(struct xfrm_state *x, struct sk_buff *skb,  netdev_features
 			xo->seq.low += skb_shinfo(skb)->gso_segs;
 	}
 
+	if (xo->seq.low < seq)
+		xo->seq.hi++;
+
 	esp.seqno = cpu_to_be64(xo->seq.low + ((u64)xo->seq.hi << 32));
 
 	len = skb->len - sizeof(struct ipv6hdr);

net/xfrm/xfrm_device.c

@@ -97,6 +97,18 @@ static void xfrm_outer_mode_prep(struct xfrm_state *x, struct sk_buff *skb)
 	}
 }
 
+static inline bool xmit_xfrm_check_overflow(struct sk_buff *skb)
+{
+	struct xfrm_offload *xo = xfrm_offload(skb);
+	__u32 seq = xo->seq.low;
+
+	seq += skb_shinfo(skb)->gso_segs;
+	if (unlikely(seq < xo->seq.low))
+		return true;
+
+	return false;
+}
+
 struct sk_buff *validate_xmit_xfrm(struct sk_buff *skb, netdev_features_t features, bool *again)
 {
 	int err;
@@ -134,7 +146,8 @@ struct sk_buff *validate_xmit_xfrm(struct sk_buff *skb, netdev_features_t featur
 		return skb;
 	}
 
-	if (skb_is_gso(skb) && unlikely(x->xso.dev != dev)) {
+	if (skb_is_gso(skb) && (unlikely(x->xso.dev != dev) ||
+				unlikely(xmit_xfrm_check_overflow(skb)))) {
 		struct sk_buff *segs;
 
 		/* Packet got rerouted, fixup features and segment it. */

net/xfrm/xfrm_replay.c

@@ -714,7 +714,7 @@ static int xfrm_replay_overflow_offload_esn(struct xfrm_state *x, struct sk_buff
 			oseq += skb_shinfo(skb)->gso_segs;
 		}
 
-		if (unlikely(oseq < replay_esn->oseq)) {
+		if (unlikely(xo->seq.low < replay_esn->oseq)) {
 			XFRM_SKB_CB(skb)->seq.output.hi = ++oseq_hi;
 			xo->seq.hi = oseq_hi;
 			replay_esn->oseq_hi = oseq_hi;