[NET]: Added GSO header verification

When GSO packets come from an untrusted source (e.g., a Xen guest domain),
we need to verify the header integrity before passing it to the hardware.

Since the first step in GSO is to verify the header, we can reuse that
code by adding a new bit to gso_type: SKB_GSO_DODGY.  Packets with this
bit set can only be fed directly to devices with the corresponding bit
NETIF_F_GSO_ROBUST.  If the device doesn't have that bit, then the skb
is fed to the GSO engine which will allow the packet to be sent to the
hardware if it passes the header check.

This patch changes the sg flag to a full features flag.  The same method
can be used to implement TSO ECN support.  We simply have to mark packets
with CWR set with SKB_GSO_ECN so that only hardware with a corresponding
NETIF_F_TSO_ECN can accept them.  The GSO engine can either fully segment
the packet, or segment the first MTU and pass the rest to the hardware for
further segmentation.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 27 insertions, 11 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index f1c52cb..4f20149 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1190,11 +1190,14 @@ out:
 /**
  *	skb_gso_segment - Perform segmentation on skb.
  *	@skb: buffer to segment
- *	@sg: whether scatter-gather is supported on the target.
+ *	@features: features for the output path (see dev->features)
  *
  *	This function segments the given skb and returns a list of segments.
+ *
+ *	It may return NULL if the skb requires no segmentation.  This is
+ *	only possible when GSO is used for verifying header integrity.
  */
-struct sk_buff *skb_gso_segment(struct sk_buff *skb, int sg)
+struct sk_buff *skb_gso_segment(struct sk_buff *skb, int features)
 {
 	struct sk_buff *segs = ERR_PTR(-EPROTONOSUPPORT);
 	struct packet_type *ptype;
@@ -1210,12 +1213,14 @@ struct sk_buff *skb_gso_segment(struct sk_buff *skb, int sg)
 	rcu_read_lock();
 	list_for_each_entry_rcu(ptype, &ptype_base[ntohs(type) & 15], list) {
 		if (ptype->type == type && !ptype->dev && ptype->gso_segment) {
-			segs = ptype->gso_segment(skb, sg);
+			segs = ptype->gso_segment(skb, features);
 			break;
 		}
 	}
 	rcu_read_unlock();
 
+	__skb_push(skb, skb->data - skb->mac.raw);
+
 	return segs;
 }
 
@@ -1291,9 +1296,15 @@ static int dev_gso_segment(struct sk_buff *skb)
 {
 	struct net_device *dev = skb->dev;
 	struct sk_buff *segs;
+	int features = dev->features & ~(illegal_highdma(dev, skb) ?
+					 NETIF_F_SG : 0);
+
+	segs = skb_gso_segment(skb, features);
+
+	/* Verifying header integrity only. */
+	if (!segs)
+		return 0;
 
-	segs = skb_gso_segment(skb, dev->features & NETIF_F_SG &&
-				    !illegal_highdma(dev, skb));
 	if (unlikely(IS_ERR(segs)))
 		return PTR_ERR(segs);
 
@@ -1310,13 +1321,17 @@ int dev_hard_start_xmit(struct sk_buff *skb, struct net_device *dev)
 		if (netdev_nit)
 			dev_queue_xmit_nit(skb, dev);
 
-		if (!netif_needs_gso(dev, skb))
-			return dev->hard_start_xmit(skb, dev);
+		if (netif_needs_gso(dev, skb)) {
+			if (unlikely(dev_gso_segment(skb)))
+				goto out_kfree_skb;
+			if (skb->next)
+				goto gso;
+		}
 
-		if (unlikely(dev_gso_segment(skb)))
-			goto out_kfree_skb;
+		return dev->hard_start_xmit(skb, dev);
 	}
 
+gso:
 	do {
 		struct sk_buff *nskb = skb->next;
 		int rc;
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 6edbb90..dfef9ee 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1848,13 +1848,13 @@ EXPORT_SYMBOL_GPL(skb_pull_rcsum);
 /**
  *	skb_segment - Perform protocol segmentation on skb.
  *	@skb: buffer to segment
- *	@sg: whether scatter-gather can be used for generated segments
+ *	@features: features for the output path (see dev->features)
  *
  *	This function performs segmentation on the given skb.  It returns
  *	the segment at the given position.  It returns NULL if there are
  *	no more segments to generate, or when an error is encountered.
  */
-struct sk_buff *skb_segment(struct sk_buff *skb, int sg)
+struct sk_buff *skb_segment(struct sk_buff *skb, int features)
 {
 	struct sk_buff *segs = NULL;
 	struct sk_buff *tail = NULL;
@@ -1863,6 +1863,7 @@ struct sk_buff *skb_segment(struct sk_buff *skb, int sg)
 	unsigned int offset = doffset;
 	unsigned int headroom;
 	unsigned int len;
+	int sg = features & NETIF_F_SG;
 	int nfrags = skb_shinfo(skb)->nr_frags;
 	int err = -ENOMEM;
 	int i = 0;