net: Fix save software checksum complete

Geert reported issues regarding checksum complete and UDP.
The logic introduced in commit 7e3cead5172927732f51fde
("net: Save software checksum complete") is not correct.

This patch:
1) Restores code in __skb_checksum_complete_header except for setting
   CHECKSUM_UNNECESSARY. This function may be calculating checksum on
   something less than skb->len.
2) Adds saving checksum to __skb_checksum_complete. The full packet
   checksum 0..skb->len is calculated without adding in pseudo header.
   This value is saved in skb->csum and then the pseudo header is added
   to that to derive the checksum for validation.
3) In both __skb_checksum_complete_header and __skb_checksum_complete,
   set skb->csum_valid to whether checksum of zero was computed. This
   allows skb_csum_unnecessary to return true without changing to
   CHECKSUM_UNNECESSARY which was done previously.
4) Copy new csum related bits in __copy_skb_header.

Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 29 insertions, 10 deletions

diff --git a/net/core/datagram.c b/net/core/datagram.c
index 6b1c04ca1d50..488dd1a825c0 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -739,22 +739,38 @@ __sum16 __skb_checksum_complete_head(struct sk_buff *skb, int len)
         __sum16 sum;
 
         sum = csum_fold(skb_checksum(skb, 0, len, skb->csum));
-        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;
-
+        if (likely(!sum)) {
+                if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE) &&
+                    !skb->csum_complete_sw)
+                        netdev_rx_csum_fault(skb->dev);
+        }
+        skb->csum_valid = !sum;
         return sum;
 }
 EXPORT_SYMBOL(__skb_checksum_complete_head);
 
 __sum16 __skb_checksum_complete(struct sk_buff *skb)
 {
-        return __skb_checksum_complete_head(skb, skb->len);
+        __wsum csum;
+        __sum16 sum;
+
+        csum = skb_checksum(skb, 0, skb->len, 0);
+
+        /* skb->csum holds pseudo checksum */
+        sum = csum_fold(csum_add(skb->csum, csum));
+        if (likely(!sum)) {
+                if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE) &&
+                    !skb->csum_complete_sw)
+                        netdev_rx_csum_fault(skb->dev);
+        }
+
+        /* Save full packet checksum */
+        skb->csum = csum;
+        skb->ip_summed = CHECKSUM_COMPLETE;
+        skb->csum_complete_sw = 1;
+        skb->csum_valid = !sum;
+
+        return sum;
 }
 EXPORT_SYMBOL(__skb_checksum_complete);
 
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index bf92824af3f7..9cd5344fad73 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -689,6 +689,9 @@ static void __copy_skb_header(struct sk_buff *new, const struct sk_buff *old)
         new->ooo_okay           = old->ooo_okay;
         new->no_fcs             = old->no_fcs;
         new->encapsulation      = old->encapsulation;
+        new->encap_hdr_csum     = old->encap_hdr_csum;
+        new->csum_valid         = old->csum_valid;
+        new->csum_complete_sw   = old->csum_complete_sw;
 #ifdef CONFIG_XFRM
         new->sp                 = secpath_get(old->sp);
 #endif