net: fix skb_add_data_nocache() to calc csum correctly

commit c6e1a0d12ca7b4f22c58e55a16beacfb7d3d8462 broken the calc (net: Allow no-cache copy from user on transmit)
of checksum, which may cause some tcp packets be dropped because incorrect checksum. ssh does not work under today's net-next-2.6 tree.

Signed-off-by Wei Yongjun <[email protected]>

---
 include/net/sock.h |   15 ++++++++-------

 1 files changed, 8 insertions(+), 7 deletions(-)

include/net/sock.h +2 -2

index 43bd515..9cbf23c 100644
@@ -1392,14 +1392,14 @@ static inline void sk_nocaps_add(struct sock *sk, int flags)
 
  static inline int skb_do_copy_data_nocache(struct sock *sk, struct sk_buff *skb,
                                           char __user *from, char *to,
-                                          int copy)
+                                          int copy, int offset)
  {
        if (skb->ip_summed == CHECKSUM_NONE) {
                int err = 0;
                __wsum csum = csum_and_copy_from_user(from, to, copy, 0, &err);
                if (err)
                        return err;
-               skb->csum = csum_block_add(skb->csum, csum, skb->len);
+               skb->csum = csum_block_add(skb->csum, csum, offset);
        } else if (sk->sk_route_caps & NETIF_F_NOCACHE_COPY) {

               if (!access_ok(VERIFY_READ, from, copy) || __copy_from_user_nocache(to, from, copy))

include/net/sock.h +6 -6

@@ -1413,11 +1413,12 @@ static inline int skb_do_copy_data_nocache(struct sock *sk, struct sk_buff *skb,
  static inline int skb_add_data_nocache(struct sock *sk, struct sk_buff *skb,
                                       char __user *from, int copy)
  {
-       int err;
+       int err, offset = skb->len;
 
-       err = skb_do_copy_data_nocache(sk, skb, from, skb_put(skb, copy), copy);
+       err = skb_do_copy_data_nocache(sk, skb, from, skb_put(skb, copy),
+                                      copy, offset);
        if (err)
-               __skb_trim(skb, skb->len);
+               __skb_trim(skb, offset);
 
        return err;
  }

@@ -1429,8 +1430,8 @@ static inline int skb_copy_to_page_nocache(struct sock *sk, char __user *from,
  {
        int err;
 
-       err = skb_do_copy_data_nocache(sk, skb, from,
-                                      page_address(page) + off, copy);
+       err = skb_do_copy_data_nocache(sk, skb, from, page_address(page) + off,
+                                      copy, skb->len);
        if (err)
                return err;
 
--

1.6.5.2

Nice catch.

Acked-by Tom Herbert <[email protected]>

Quoted 7 lines · Wei Yongjun

commit c6e1a0d12ca7b4f22c58e55a16beacfb7d3d8462 broken the calc (net: Allow no-cache copy from user on transmit)
of checksum, which may cause some tcp packets be dropped because incorrect checksum. ssh does not work under today's net-next-2.6 tree.

Signed-off-by Wei Yongjun <[email protected]>