datapath: Make our checksumming more closely match skb_checksum_help().

Our code that handles checksumming does essentially the same thing
as skb_checksum_help() except it folds the process into copying to
userspace.  This makes the two functions more closely resemble
each other in structure, including adding a couple of BUG() checks.
This should have no functional change but makes comparision easier
when debugging.

diff --git a/datapath/datapath.c b/datapath/datapath.c
index 8991e35..8833bc1 100644 (file)
--- a/datapath/datapath.c
+++ b/datapath/datapath.c
@@ -2196,18 +2196,13 @@ success:
                        int csum_start, csum_offset;
 
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,22)
-                       /* Until 2.6.22, the start of the transport header was
-                        * also the start of data to be checksummed.  Linux
-                        * 2.6.22 introduced the csum_start field for this
-                        * purpose, but we should point the transport header to
-                        * it anyway for backward compatibility, as
-                        * dev_queue_xmit() does even in 2.6.28. */
-                       skb_set_transport_header(skb, skb->csum_start - skb_headroom(skb));
+                       csum_start = skb->csum_start - skb_headroom(skb);
                        csum_offset = skb->csum_offset;
 #else
+                       csum_start = skb_transport_header(skb) - skb->data;
                        csum_offset = skb->csum;
 #endif
-                       csum_start = skb_transport_header(skb) - skb->data;
+                       BUG_ON(csum_start >= skb_headlen(skb));
                        retval = skb_copy_and_csum_datagram(skb, csum_start, buf + csum_start,
                                                            copy_bytes - csum_start, &csum);
                        if (!retval) {
@@ -2215,6 +2210,8 @@ success:
 
                                copy_bytes = csum_start;
                                csump = (__sum16 __user *)(buf + csum_start + csum_offset);
+
+                               BUG_ON((char *)csump + sizeof(__sum16) > buf + nbytes);
                                put_user(csum_fold(csum), csump);
                        }
                } else