[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, 9 insertions, 5 deletions

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 461216b47948..8d157157bf8e 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -1097,7 +1097,7 @@ int inet_sk_rebuild_header(struct sock *sk)
 
 EXPORT_SYMBOL(inet_sk_rebuild_header);
 
-static struct sk_buff *inet_gso_segment(struct sk_buff *skb, int sg)
+static struct sk_buff *inet_gso_segment(struct sk_buff *skb, int features)
 {
         struct sk_buff *segs = ERR_PTR(-EINVAL);
         struct iphdr *iph;
@@ -1126,10 +1126,10 @@ static struct sk_buff *inet_gso_segment(struct sk_buff *skb, int sg)
         rcu_read_lock();
         ops = rcu_dereference(inet_protos[proto]);
         if (ops && ops->gso_segment)
-                segs = ops->gso_segment(skb, sg);
+                segs = ops->gso_segment(skb, features);
         rcu_read_unlock();
 
-        if (IS_ERR(segs))
+        if (!segs || unlikely(IS_ERR(segs)))
                 goto out;
 
         skb = segs;
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index c04176be7ed1..0336422c88a0 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2145,7 +2145,7 @@ int compat_tcp_getsockopt(struct sock *sk, int level, int optname,
 EXPORT_SYMBOL(compat_tcp_getsockopt);
 #endif
 
-struct sk_buff *tcp_tso_segment(struct sk_buff *skb, int sg)
+struct sk_buff *tcp_tso_segment(struct sk_buff *skb, int features)
 {
         struct sk_buff *segs = ERR_PTR(-EINVAL);
         struct tcphdr *th;
@@ -2166,10 +2166,14 @@ struct sk_buff *tcp_tso_segment(struct sk_buff *skb, int sg)
         if (!pskb_may_pull(skb, thlen))
                 goto out;
 
+        segs = NULL;
+        if (skb_gso_ok(skb, features | NETIF_F_GSO_ROBUST))
+                goto out;
+
         oldlen = (u16)~skb->len;
         __skb_pull(skb, thlen);
 
-        segs = skb_segment(skb, sg);
+        segs = skb_segment(skb, features);
         if (IS_ERR(segs))
                 goto out;