[PATCH net-next] net: sock: adapt SOCK_MIN_RCVBUF and SOCK_MIN_SNDBUF

[Daniel Borkmann <dborkman@redhat.com>]

The current situation is that SOCK_MIN_RCVBUF is 2048 + sizeof(struct sk_buff))
while SOCK_MIN_SNDBUF is 2048. Since in both cases, skb->truesize is used for
sk_{r,w}mem_alloc accounting, we should have both sizes equal and adjusted
through the macro SKB_TRUESIZE(), which is also used elsewhere to adjust sk
buffer sizes. The minor adaption in sk_stream_moderate_sndbuf() is to silence
a warning by using a typed max macro, as similarly done in SOCK_MIN_RCVBUF
occurences, that would appear otherwise.

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
---
 include/net/sock.h | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index ac8e181..189ef98 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -2045,18 +2045,19 @@ static inline void sk_wake_async(struct sock *sk, int how, int band)
 		sock_wake_async(sk->sk_socket, how, band);
 }
 
-#define SOCK_MIN_SNDBUF 2048
 /*
- * Since sk_rmem_alloc sums skb->truesize, even a small frame might need
- * sizeof(sk_buff) + MTU + padding, unless net driver perform copybreak
+ * Since sk_{r,w}mem_alloc sums skb->truesize, even a small frame might
+ * need sizeof(sk_buff) + sizeof(skb_shared_info) + MTU + padding, unless
+ * net driver perform copybreak.
  */
-#define SOCK_MIN_RCVBUF (2048 + sizeof(struct sk_buff))
+#define SOCK_MIN_RCVBUF		SKB_TRUESIZE(2048)
+#define SOCK_MIN_SNDBUF		SKB_TRUESIZE(2048)
 
 static inline void sk_stream_moderate_sndbuf(struct sock *sk)
 {
 	if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK)) {
 		sk->sk_sndbuf = min(sk->sk_sndbuf, sk->sk_wmem_queued >> 1);
-		sk->sk_sndbuf = max(sk->sk_sndbuf, SOCK_MIN_SNDBUF);
+		sk->sk_sndbuf = max_t(u32, sk->sk_sndbuf, SOCK_MIN_SNDBUF);
 	}
 }
 
-- 
1.7.11.7