[NET] gso: Fix up GSO packets with broken checksums

Certain subsystems in the stack (e.g., netfilter) can break the partial
checksum on GSO packets.  Until they're fixed, this patch allows this to
work by recomputing the partial checksums through the GSO mechanism.

Once they've all been converted to update the partial checksum instead of
clearing it, this workaround can be removed.

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

2 files changed, 54 insertions, 0 deletions

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 318d4674faa1..c84a32070f8d 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -1097,6 +1097,40 @@ int inet_sk_rebuild_header(struct sock *sk)
 
 EXPORT_SYMBOL(inet_sk_rebuild_header);
 
+static int inet_gso_send_check(struct sk_buff *skb)
+{
+        struct iphdr *iph;
+        struct net_protocol *ops;
+        int proto;
+        int ihl;
+        int err = -EINVAL;
+
+        if (unlikely(!pskb_may_pull(skb, sizeof(*iph))))
+                goto out;
+
+        iph = skb->nh.iph;
+        ihl = iph->ihl * 4;
+        if (ihl < sizeof(*iph))
+                goto out;
+
+        if (unlikely(!pskb_may_pull(skb, ihl)))
+                goto out;
+
+        skb->h.raw = __skb_pull(skb, ihl);
+        iph = skb->nh.iph;
+        proto = iph->protocol & (MAX_INET_PROTOS - 1);
+        err = -EPROTONOSUPPORT;
+
+        rcu_read_lock();
+        ops = rcu_dereference(inet_protos[proto]);
+        if (likely(ops && ops->gso_send_check))
+                err = ops->gso_send_check(skb);
+        rcu_read_unlock();
+
+out:
+        return err;
+}
+
 static struct sk_buff *inet_gso_segment(struct sk_buff *skb, int features)
 {
         struct sk_buff *segs = ERR_PTR(-EINVAL);
@@ -1162,6 +1196,7 @@ static struct net_protocol igmp_protocol = {
 static struct net_protocol tcp_protocol = {
         .handler =      tcp_v4_rcv,
         .err_handler =  tcp_v4_err,
+        .gso_send_check = tcp_v4_gso_send_check,
         .gso_segment =  tcp_tso_segment,
         .no_policy =    1,
 };
@@ -1208,6 +1243,7 @@ static int ipv4_proc_init(void);
 static struct packet_type ip_packet_type = {
         .type = __constant_htons(ETH_P_IP),
         .func = ip_rcv,
+        .gso_send_check = inet_gso_send_check,
         .gso_segment = inet_gso_segment,
 };
 
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 5a886e6efbbe..a891133f00e4 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -496,6 +496,24 @@ void tcp_v4_send_check(struct sock *sk, int len, struct sk_buff *skb)
         }
 }
 
+int tcp_v4_gso_send_check(struct sk_buff *skb)
+{
+        struct iphdr *iph;
+        struct tcphdr *th;
+
+        if (!pskb_may_pull(skb, sizeof(*th)))
+                return -EINVAL;
+
+        iph = skb->nh.iph;
+        th = skb->h.th;
+
+        th->check = 0;
+        th->check = ~tcp_v4_check(th, skb->len, iph->saddr, iph->daddr, 0);
+        skb->csum = offsetof(struct tcphdr, check);
+        skb->ip_summed = CHECKSUM_HW;
+        return 0;
+}
+
 /*
  *      This routine will send an RST to the other tcp.
  *