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>

2 files changed, 16 insertions, 3 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 2c154976394b..44727b5d4981 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2360,8 +2360,6 @@ int skb_copy_datagram_const_iovec(const struct sk_buff *from, int offset,
 void skb_free_datagram(struct sock *sk, struct sk_buff *skb);
 void skb_free_datagram_locked(struct sock *sk, struct sk_buff *skb);
 int skb_kill_datagram(struct sock *sk, struct sk_buff *skb, unsigned int flags);
-__wsum skb_checksum(const struct sk_buff *skb, int offset, int len,
-                    __wsum csum);
 int skb_copy_bits(const struct sk_buff *skb, int offset, void *to, int len);
 int skb_store_bits(struct sk_buff *skb, int offset, const void *from, int len);
 __wsum skb_copy_and_csum_bits(const struct sk_buff *skb, int offset, u8 *to,
@@ -2373,9 +2371,18 @@ void skb_copy_and_csum_dev(const struct sk_buff *skb, u8 *to);
 void skb_split(struct sk_buff *skb, struct sk_buff *skb1, const u32 len);
 int skb_shift(struct sk_buff *tgt, struct sk_buff *skb, int shiftlen);
 void skb_scrub_packet(struct sk_buff *skb, bool xnet);
-
 struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features);
 
+struct skb_checksum_ops {
+        __wsum (*update)(const void *mem, int len, __wsum wsum);
+        __wsum (*combine)(__wsum csum, __wsum csum2, int offset, int len);
+};
+
+__wsum __skb_checksum(const struct sk_buff *skb, int offset, int len,
+                      __wsum csum, const struct skb_checksum_ops *ops);
+__wsum skb_checksum(const struct sk_buff *skb, int offset, int len,
+                    __wsum csum);
+
 static inline void *skb_header_pointer(const struct sk_buff *skb, int offset,
                                        int len, void *buffer)
 {
diff --git a/include/net/checksum.h b/include/net/checksum.h
index 8f59ca50477c..15f33fde826e 100644
--- a/include/net/checksum.h
+++ b/include/net/checksum.h
@@ -79,6 +79,12 @@ csum_block_add(__wsum csum, __wsum csum2, int offset)
 }
 
 static inline __wsum
+csum_block_add_ext(__wsum csum, __wsum csum2, int offset, int len)
+{
+        return csum_block_add(csum, csum2, offset);
+}
+
+static inline __wsum
 csum_block_sub(__wsum csum, __wsum csum2, int offset)
 {
         u32 sum = (__force u32)csum2;