net: Introduce skb_send_sock() for sock_map

We only have skb_send_sock_locked() which requires callers
to use lock_sock(). Introduce a variant skb_send_sock()
which locks on its own, callers do not need to lock it
any more. This will save us from adding a ->sendmsg_locked
for each protocol.

To reuse the code, pass function pointers to __skb_send_sock()
and build skb_send_sock() and skb_send_sock_locked() on top.

Signed-off-by: Cong Wang <cong.wang@bytedance.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
Link: https://lore.kernel.org/bpf/20210331023237.41094-4-xiyou.wangcong@gmail.com

include/linux/skbuff.h

@@ -3626,6 +3626,7 @@ int skb_splice_bits(struct sk_buff *skb, struct sock *sk, unsigned int offset,
 		    unsigned int flags);
 int skb_send_sock_locked(struct sock *sk, struct sk_buff *skb, int offset,
 			 int len);
+int skb_send_sock(struct sock *sk, struct sk_buff *skb, int offset, int len);
 void skb_copy_and_csum_dev(const struct sk_buff *skb, u8 *to);
 unsigned int skb_zerocopy_headlen(const struct sk_buff *from);
 int skb_zerocopy(struct sk_buff *to, struct sk_buff *from,

net/core/skbuff.c

@@ -2500,9 +2500,32 @@ int skb_splice_bits(struct sk_buff *skb, struct sock *sk, unsigned int offset,
 }
 EXPORT_SYMBOL_GPL(skb_splice_bits);
 
-/* Send skb data on a socket. Socket must be locked. */
-int skb_send_sock_locked(struct sock *sk, struct sk_buff *skb, int offset,
-			 int len)
+static int sendmsg_unlocked(struct sock *sk, struct msghdr *msg,
+			    struct kvec *vec, size_t num, size_t size)
+{
+	struct socket *sock = sk->sk_socket;
+
+	if (!sock)
+		return -EINVAL;
+	return kernel_sendmsg(sock, msg, vec, num, size);
+}
+
+static int sendpage_unlocked(struct sock *sk, struct page *page, int offset,
+			     size_t size, int flags)
+{
+	struct socket *sock = sk->sk_socket;
+
+	if (!sock)
+		return -EINVAL;
+	return kernel_sendpage(sock, page, offset, size, flags);
+}
+
+typedef int (*sendmsg_func)(struct sock *sk, struct msghdr *msg,
+			    struct kvec *vec, size_t num, size_t size);
+typedef int (*sendpage_func)(struct sock *sk, struct page *page, int offset,
+			     size_t size, int flags);
+static int __skb_send_sock(struct sock *sk, struct sk_buff *skb, int offset,
+			   int len, sendmsg_func sendmsg, sendpage_func sendpage)
 {
 	unsigned int orig_len = len;
 	struct sk_buff *head = skb;
@@ -2522,7 +2545,8 @@ int skb_send_sock_locked(struct sock *sk, struct sk_buff *skb, int offset,
 		memset(&msg, 0, sizeof(msg));
 		msg.msg_flags = MSG_DONTWAIT;
 
-		ret = kernel_sendmsg_locked(sk, &msg, &kv, 1, slen);
+		ret = INDIRECT_CALL_2(sendmsg, kernel_sendmsg_locked,
+				      sendmsg_unlocked, sk, &msg, &kv, 1, slen);
 		if (ret <= 0)
 			goto error;
 
@@ -2553,9 +2577,11 @@ int skb_send_sock_locked(struct sock *sk, struct sk_buff *skb, int offset,
 		slen = min_t(size_t, len, skb_frag_size(frag) - offset);
 
 		while (slen) {
-			ret = kernel_sendpage_locked(sk, skb_frag_page(frag),
-						     skb_frag_off(frag) + offset,
-						     slen, MSG_DONTWAIT);
+			ret = INDIRECT_CALL_2(sendpage, kernel_sendpage_locked,
+					      sendpage_unlocked, sk,
+					      skb_frag_page(frag),
+					      skb_frag_off(frag) + offset,
+					      slen, MSG_DONTWAIT);
 			if (ret <= 0)
 				goto error;
 
@@ -2587,8 +2613,23 @@ int skb_send_sock_locked(struct sock *sk, struct sk_buff *skb, int offset,
 error:
 	return orig_len == len ? ret : orig_len - len;
 }
+
+/* Send skb data on a socket. Socket must be locked. */
+int skb_send_sock_locked(struct sock *sk, struct sk_buff *skb, int offset,
+			 int len)
+{
+	return __skb_send_sock(sk, skb, offset, len, kernel_sendmsg_locked,
+			       kernel_sendpage_locked);
+}
 EXPORT_SYMBOL_GPL(skb_send_sock_locked);
 
+/* Send skb data on a socket. Socket must be unlocked. */
+int skb_send_sock(struct sock *sk, struct sk_buff *skb, int offset, int len)
+{
+	return __skb_send_sock(sk, skb, offset, len, sendmsg_unlocked,
+			       sendpage_unlocked);
+}
+
 /**
  *	skb_store_bits - store bits from kernel buffer to skb
  *	@skb: destination buffer