[NET]: Revert sk_buff walker cleanups.

This reverts eefa3906283a2b60a6d02a2cda593a7d7d7946c5

The simplification made in that change works with the assumption that
the 'offset' parameter to these functions is always positive or zero,
which is not true.  It can be and often is negative in order to access
SKB header values in front of skb->data.

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 14 insertions, 8 deletions

diff --git a/net/xfrm/xfrm_algo.c b/net/xfrm/xfrm_algo.c
index be529c4241a6..6249a9405bb8 100644
--- a/net/xfrm/xfrm_algo.c
+++ b/net/xfrm/xfrm_algo.c
@@ -532,8 +532,8 @@ EXPORT_SYMBOL_GPL(xfrm_count_enc_supported);
 int skb_icv_walk(const struct sk_buff *skb, struct hash_desc *desc,
                  int offset, int len, icv_update_fn_t icv_update)
 {
-        int end = skb_headlen(skb);
-        int i, copy = end - offset;
+        int start = skb_headlen(skb);
+        int i, copy = start - offset;
         int err;
         struct scatterlist sg;
 
@@ -556,9 +556,11 @@ int skb_icv_walk(const struct sk_buff *skb, struct hash_desc *desc,
         }
 
         for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
-                BUG_TRAP(len >= 0);
+                int end;
 
-                end = offset + skb_shinfo(skb)->frags[i].size;
+                BUG_TRAP(start <= offset + len);
+
+                end = start + skb_shinfo(skb)->frags[i].size;
                 if ((copy = end - offset) > 0) {
                         skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
 
@@ -566,7 +568,7 @@ int skb_icv_walk(const struct sk_buff *skb, struct hash_desc *desc,
                                 copy = len;
 
                         sg.page = frag->page;
-                        sg.offset = frag->page_offset;
+                        sg.offset = frag->page_offset + offset-start;
                         sg.length = copy;
 
                         err = icv_update(desc, &sg, copy);
@@ -577,19 +579,22 @@ int skb_icv_walk(const struct sk_buff *skb, struct hash_desc *desc,
                                 return 0;
                         offset += copy;
                 }
+                start = end;
         }
 
         if (skb_shinfo(skb)->frag_list) {
                 struct sk_buff *list = skb_shinfo(skb)->frag_list;
 
                 for (; list; list = list->next) {
-                        BUG_TRAP(len >= 0);
+                        int end;
+
+                        BUG_TRAP(start <= offset + len);
 
-                        end = offset + list->len;
+                        end = start + list->len;
                         if ((copy = end - offset) > 0) {
                                 if (copy > len)
                                         copy = len;
-                                err = skb_icv_walk(list, desc, 0,
+                                err = skb_icv_walk(list, desc, offset-start,
                                                    copy, icv_update);
                                 if (unlikely(err))
                                         return err;
@@ -597,6 +602,7 @@ int skb_icv_walk(const struct sk_buff *skb, struct hash_desc *desc,
                                         return 0;
                                 offset += copy;
                         }
+                        start = end;
                 }
         }
         BUG_ON(len);