net: Save software checksum complete

In skb_checksum complete, if we need to compute the checksum for the
packet (via skb_checksum) save the result as CHECKSUM_COMPLETE.
Subsequent checksum verification can use this.

Also, added csum_complete_sw flag to distinguish between software and
hardware generated checksum complete, we should always be able to trust
the software computation.

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

4 files changed, 17 insertions, 9 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 72a53805858a..5b5cd3189c98 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -573,7 +573,8 @@ struct sk_buff {
         __u8                    encapsulation:1;
         __u8                    encap_hdr_csum:1;
         __u8                    csum_valid:1;
-        /* 4/6 bit hole (depending on ndisc_nodetype presence) */
+        __u8                    csum_complete_sw:1;
+        /* 3/5 bit hole (depending on ndisc_nodetype presence) */
         kmemcheck_bitfield_end(flags2);
 
 #if defined CONFIG_NET_DMA || defined CONFIG_NET_RX_BUSY_POLL
diff --git a/net/core/datagram.c b/net/core/datagram.c
index a16ed7bbe376..6b1c04ca1d50 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -739,11 +739,15 @@ __sum16 __skb_checksum_complete_head(struct sk_buff *skb, int len)
         __sum16 sum;
 
         sum = csum_fold(skb_checksum(skb, 0, len, skb->csum));
-        if (likely(!sum)) {
-                if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE))
-                        netdev_rx_csum_fault(skb->dev);
-                skb->ip_summed = CHECKSUM_UNNECESSARY;
-        }
+        if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE) && !sum &&
+            !skb->csum_complete_sw)
+                netdev_rx_csum_fault(skb->dev);
+
+        /* Save checksum complete for later use */
+        skb->csum = sum;
+        skb->ip_summed = CHECKSUM_COMPLETE;
+        skb->csum_complete_sw = 1;
+
         return sum;
 }
 EXPORT_SYMBOL(__skb_checksum_complete_head);
diff --git a/net/ipv4/gre_offload.c b/net/ipv4/gre_offload.c
index 24deb3928b9e..eb92deb12666 100644
--- a/net/ipv4/gre_offload.c
+++ b/net/ipv4/gre_offload.c
@@ -131,10 +131,12 @@ static __sum16 gro_skb_checksum(struct sk_buff *skb)
                 csum_partial(skb->data, skb_gro_offset(skb), 0));
         sum = csum_fold(NAPI_GRO_CB(skb)->csum);
         if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE)) {
-                if (unlikely(!sum))
+                if (unlikely(!sum) && !skb->csum_complete_sw)
                         netdev_rx_csum_fault(skb->dev);
-        } else
+        } else {
                 skb->ip_summed = CHECKSUM_COMPLETE;
+                skb->csum_complete_sw = 1;
+        }
 
         return sum;
 }
diff --git a/net/sunrpc/socklib.c b/net/sunrpc/socklib.c
index 0a648c502fc3..2df87f78e518 100644
--- a/net/sunrpc/socklib.c
+++ b/net/sunrpc/socklib.c
@@ -173,7 +173,8 @@ int csum_partial_copy_to_xdr(struct xdr_buf *xdr, struct sk_buff *skb)
                 return -1;
         if (csum_fold(desc.csum))
                 return -1;
-        if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE))
+        if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE) &&
+            !skb->csum_complete_sw)
                 netdev_rx_csum_fault(skb->dev);
         return 0;
 no_checksum: