[PATCH net] ppp: linearize and segment bridged packets when required

@@ -45,6 +45,7 @@
 #include <linux/slab.h>
 #include <linux/file.h>
 #include <linux/unaligned.h>
+#include <net/gso.h>
 #include <net/netdev_lock.h>
 #include <net/slhc_vj.h>
 #include <linux/atomic.h>

@@ -2278,6 +2279,61 @@ static bool ppp_decompress_proto(struct sk_buff *skb)
 	return pskb_may_pull(skb, 2);
 }
 
+/* Segment a GSO packet (built by PPPoE GRO, or injected with a
+ * virtio_net_hdr) before sending it to a bridged channel that does
+ * not accept GSO packets.
+ * skb->data points to the PPP protocol field, which is replicated
+ * in front of each segment.
+ * Returns a list of segments, or NULL if the packet was dropped.
+ */
+static struct sk_buff *ppp_bridge_gso_segment(struct sk_buff *skb,
+					      netdev_features_t features)
+{
+	struct sk_buff *segs;
+
+	if (!pskb_may_pull(skb, PPP_PROTO_LEN))
+		goto drop;
+
+	switch (get_unaligned((__be16 *)skb->data)) {
+	case htons(PPP_IP):
+		skb->protocol = htons(ETH_P_IP);
+		break;
+	case htons(PPP_IPV6):
+		skb->protocol = htons(ETH_P_IPV6);
+		break;
+	default:
+		goto drop;
+	}
+	skb_set_network_header(skb, PPP_PROTO_LEN);
+
+	/* No checksum offload: skb_segment() computes the checksums. */
+	segs = skb_gso_segment(skb, features);
+	if (IS_ERR_OR_NULL(segs))
+		goto drop;
+
+	consume_skb(skb);
+	return segs;
+
+drop:
+	kfree_skb(skb);
+	return NULL;
+}
+
+static void ppp_bridge_xmit(struct ppp_channel *chan, struct sk_buff *skb)
+{
+	if (!chan->direct_xmit && skb_linearize(skb))
+		goto drop;
+
+	if (!chan->xmit_offload && skb->ip_summed == CHECKSUM_PARTIAL &&
+	    skb_checksum_help(skb))
+		goto drop;
+
+	if (chan->ops->start_xmit(chan, skb))
+		return;
+drop:
+	kfree_skb(skb);
+}
+
 /* Attempt to handle a frame via. a bridged channel, if one exists.
  * If the channel is bridged, the frame is consumed by the bridge.
  * If not, the caller must handle the frame by normal recv mechanisms.

@@ -2285,6 +2341,8 @@ static bool ppp_decompress_proto(struct sk_buff *skb)
  */
 static bool ppp_channel_bridge_input(struct channel *pch, struct sk_buff *skb)
 {
+	struct sk_buff *segs, *next;
+	struct ppp_channel *chan;
 	struct channel *pchb;
 
 	rcu_read_lock();

@@ -2300,8 +2358,21 @@ static bool ppp_channel_bridge_input(struct channel *pch, struct sk_buff *skb)
 	}
 
 	skb_scrub_packet(skb, !net_eq(pch->chan_net, pchb->chan_net));
-	if (!pchb->chan->ops->start_xmit(pchb->chan, skb))
-		kfree_skb(skb);
+
+	chan = pchb->chan;
+	if (!chan->xmit_offload && skb_is_gso(skb)) {
+		/* Channels needing linear packets get linear segments,
+		 * others keep references to the original pages.
+		 */
+		segs = ppp_bridge_gso_segment(skb, chan->direct_xmit ?
+						   NETIF_F_SG : 0);
+		skb_list_walk_safe(segs, skb, next) {
+			skb_mark_not_on_list(skb);
+			ppp_bridge_xmit(chan, skb);
+		}
+	} else {
+		ppp_bridge_xmit(chan, skb);
+	}
 
 outl:
 	spin_unlock_bh(&pchb->downl);

@@ -664,6 +664,7 @@ static int pppoe_connect(struct socket *sock, struct sockaddr_unsized *uservaddr
 		po->chan.private = sk;
 		po->chan.ops = &pppoe_chan_ops;
 		po->chan.direct_xmit = true;
+		po->chan.xmit_offload = true;
 
 		error = ppp_register_net_channel(dev_net(dev), &po->chan);
 		if (error) {

@@ -43,6 +43,7 @@ struct ppp_channel {
 	void		*ppp;		/* opaque to channel */
 	int		speed;		/* transfer rate (bytes/second) */
 	bool		direct_xmit;	/* no qdisc, xmit directly */
+	bool		xmit_offload;	/* accepts GSO and CHECKSUM_PARTIAL skbs */
 };
 
 #ifdef __KERNEL__