net: skb_checksum: allow custom update/combine for walking skb

Currently, skb_checksum walks over 1) linearized, 2) frags[], and
3) frag_list data and calculats the one's complement, a 32 bit
result suitable for feeding into itself or csum_tcpudp_magic(),
but unsuitable for SCTP as we're calculating CRC32c there.

Hence, in order to not re-implement the very same function in
SCTP (and maybe other protocols) over and over again, use an
update() + combine() callback internally to allow for walking
over the skb with different algorithms.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 21 insertions, 10 deletions

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 0ab32faa520f..31aab5376cb4 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -1928,9 +1928,8 @@ fault:
 EXPORT_SYMBOL(skb_store_bits);
 
 /* Checksum skb data. */
-
-__wsum skb_checksum(const struct sk_buff *skb, int offset,
-                          int len, __wsum csum)
+__wsum __skb_checksum(const struct sk_buff *skb, int offset, int len,
+                      __wsum csum, const struct skb_checksum_ops *ops)
 {
         int start = skb_headlen(skb);
         int i, copy = start - offset;
@@ -1941,7 +1940,7 @@ __wsum skb_checksum(const struct sk_buff *skb, int offset,
         if (copy > 0) {
                 if (copy > len)
                         copy = len;
-                csum = csum_partial(skb->data + offset, copy, csum);
+                csum = ops->update(skb->data + offset, copy, csum);
                 if ((len -= copy) == 0)
                         return csum;
                 offset += copy;
@@ -1962,10 +1961,10 @@ __wsum skb_checksum(const struct sk_buff *skb, int offset,
                         if (copy > len)
                                 copy = len;
                         vaddr = kmap_atomic(skb_frag_page(frag));
-                        csum2 = csum_partial(vaddr + frag->page_offset +
-                                             offset - start, copy, 0);
+                        csum2 = ops->update(vaddr + frag->page_offset +
+                                            offset - start, copy, 0);
                         kunmap_atomic(vaddr);
-                        csum = csum_block_add(csum, csum2, pos);
+                        csum = ops->combine(csum, csum2, pos, copy);
                         if (!(len -= copy))
                                 return csum;
                         offset += copy;
@@ -1984,9 +1983,9 @@ __wsum skb_checksum(const struct sk_buff *skb, int offset,
                         __wsum csum2;
                         if (copy > len)
                                 copy = len;
-                        csum2 = skb_checksum(frag_iter, offset - start,
-                                             copy, 0);
-                        csum = csum_block_add(csum, csum2, pos);
+                        csum2 = __skb_checksum(frag_iter, offset - start,
+                                               copy, 0, ops);
+                        csum = ops->combine(csum, csum2, pos, copy);
                         if ((len -= copy) == 0)
                                 return csum;
                         offset += copy;
@@ -1998,6 +1997,18 @@ __wsum skb_checksum(const struct sk_buff *skb, int offset,
 
         return csum;
 }
+EXPORT_SYMBOL(__skb_checksum);
+
+__wsum skb_checksum(const struct sk_buff *skb, int offset,
+                    int len, __wsum csum)
+{
+        const struct skb_checksum_ops ops = {
+                .update  = csum_partial,
+                .combine = csum_block_add_ext,
+        };
+
+        return __skb_checksum(skb, offset, len, csum, &ops);
+}
 EXPORT_SYMBOL(skb_checksum);
 
 /* Both of above in one bottle. */