sctp: count both sk and asoc sndbuf with skb truesize and sctp_chunk size

Now it's confusing that asoc sndbuf_used is doing memory accounting with
SCTP_DATA_SNDSIZE(chunk) + sizeof(sk_buff) + sizeof(sctp_chunk) while sk
sk_wmem_alloc is doing that with skb->truesize + sizeof(sctp_chunk).

It also causes sctp_prsctp_prune to count with a wrong freed memory when
sndbuf_policy is not set.

To make this right and also keep consistent between asoc sndbuf_used, sk
sk_wmem_alloc and sk_wmem_queued, use skb->truesize + sizeof(sctp_chunk)
for them.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index f73e9d3..c6f2950 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -166,12 +166,9 @@ static inline void sctp_set_owner_w(struct sctp_chunk *chunk)
 	/* Save the chunk pointer in skb for sctp_wfree to use later.  */
 	skb_shinfo(chunk->skb)->destructor_arg = chunk;
 
-	asoc->sndbuf_used += SCTP_DATA_SNDSIZE(chunk) +
-				sizeof(struct sk_buff) +
-				sizeof(struct sctp_chunk);
-
 	refcount_add(sizeof(struct sctp_chunk), &sk->sk_wmem_alloc);
-	sk->sk_wmem_queued += chunk->skb->truesize;
+	asoc->sndbuf_used += chunk->skb->truesize + sizeof(struct sctp_chunk);
+	sk->sk_wmem_queued += chunk->skb->truesize + sizeof(struct sctp_chunk);
 	sk_mem_charge(sk, chunk->skb->truesize);
 }
 
@@ -8460,17 +8457,11 @@ static void sctp_wfree(struct sk_buff *skb)
 	struct sctp_association *asoc = chunk->asoc;
 	struct sock *sk = asoc->base.sk;
 
-	asoc->sndbuf_used -= SCTP_DATA_SNDSIZE(chunk) +
-				sizeof(struct sk_buff) +
-				sizeof(struct sctp_chunk);
-
-	WARN_ON(refcount_sub_and_test(sizeof(struct sctp_chunk), &sk->sk_wmem_alloc));
-
-	/*
-	 * This undoes what is done via sctp_set_owner_w and sk_mem_charge
-	 */
-	sk->sk_wmem_queued   -= skb->truesize;
 	sk_mem_uncharge(sk, skb->truesize);
+	sk->sk_wmem_queued -= skb->truesize + sizeof(struct sctp_chunk);
+	asoc->sndbuf_used -= skb->truesize + sizeof(struct sctp_chunk);
+	WARN_ON(refcount_sub_and_test(sizeof(struct sctp_chunk),
+				      &sk->sk_wmem_alloc));
 
 	if (chunk->shkey) {
 		struct sctp_shared_key *shkey = chunk->shkey;