af_unix: Add OOB support

This patch adds OOB support for AF_UNIX sockets.
The semantics is same as TCP.

The last byte of a message with the OOB flag is
treated as the OOB byte. The byte is separated into
a skb and a pointer to the skb is stored in unix_sock.
The pointer is used to enforce OOB semantics.

Signed-off-by: Rao Shoaib <rao.shoaib@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 156 insertions, 2 deletions

diff --git a/net/unix/Kconfig b/net/unix/Kconfig
index b6c4282899ec..b7f811216820 100644
--- a/net/unix/Kconfig
+++ b/net/unix/Kconfig
@@ -25,6 +25,11 @@ config UNIX_SCM
 	depends on UNIX
 	default y
 
+config	AF_UNIX_OOB
+	bool
+	depends on UNIX
+	default y
+
 config UNIX_DIAG
 	tristate "UNIX: socket monitoring interface"
 	depends on UNIX
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 256c4e31132e..ec02e70a549b 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -503,6 +503,12 @@ static void unix_sock_destructor(struct sock *sk)
 
 	skb_queue_purge(&sk->sk_receive_queue);
 
+#if IS_ENABLED(CONFIG_AF_UNIX_OOB)
+	if (u->oob_skb) {
+		kfree_skb(u->oob_skb);
+		u->oob_skb = NULL;
+	}
+#endif
 	WARN_ON(refcount_read(&sk->sk_wmem_alloc));
 	WARN_ON(!sk_unhashed(sk));
 	WARN_ON(sk->sk_socket);
@@ -1889,6 +1895,46 @@ out:
  */
 #define UNIX_SKB_FRAGS_SZ (PAGE_SIZE << get_order(32768))
 
+#if (IS_ENABLED(CONFIG_AF_UNIX_OOB))
+static int queue_oob(struct socket *sock, struct msghdr *msg, struct sock *other)
+{
+	struct unix_sock *ousk = unix_sk(other);
+	struct sk_buff *skb;
+	int err = 0;
+
+	skb = sock_alloc_send_skb(sock->sk, 1, msg->msg_flags & MSG_DONTWAIT, &err);
+
+	if (!skb)
+		return err;
+
+	skb_put(skb, 1);
+	skb->len = 1;
+	err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, 1);
+
+	if (err) {
+		kfree_skb(skb);
+		return err;
+	}
+
+	unix_state_lock(other);
+	maybe_add_creds(skb, sock, other);
+	skb_get(skb);
+
+	if (ousk->oob_skb)
+		kfree_skb(ousk->oob_skb);
+
+	ousk->oob_skb = skb;
+
+	scm_stat_add(other, skb);
+	skb_queue_tail(&other->sk_receive_queue, skb);
+	sk_send_sigurg(other);
+	unix_state_unlock(other);
+	other->sk_data_ready(other);
+
+	return err;
+}
+#endif
+
 static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,
 			       size_t len)
 {
@@ -1907,8 +1953,14 @@ static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,
 		return err;
 
 	err = -EOPNOTSUPP;
-	if (msg->msg_flags&MSG_OOB)
-		goto out_err;
+	if (msg->msg_flags & MSG_OOB) {
+#if (IS_ENABLED(CONFIG_AF_UNIX_OOB))
+		if (len)
+			len--;
+		else
+#endif
+			goto out_err;
+	}
 
 	if (msg->msg_namelen) {
 		err = sk->sk_state == TCP_ESTABLISHED ? -EISCONN : -EOPNOTSUPP;
@@ -1973,6 +2025,15 @@ static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,
 		sent += size;
 	}
 
+#if (IS_ENABLED(CONFIG_AF_UNIX_OOB))
+	if (msg->msg_flags & MSG_OOB) {
+		err = queue_oob(sock, msg, other);
+		if (err)
+			goto out_err;
+		sent++;
+	}
+#endif
+
 	scm_destroy(&scm);
 
 	return sent;
@@ -2358,6 +2419,59 @@ struct unix_stream_read_state {
 	unsigned int splice_flags;
 };
 
+#if IS_ENABLED(CONFIG_AF_UNIX_OOB)
+static int unix_stream_recv_urg(struct unix_stream_read_state *state)
+{
+	struct socket *sock = state->socket;
+	struct sock *sk = sock->sk;
+	struct unix_sock *u = unix_sk(sk);
+	int chunk = 1;
+
+	if (sock_flag(sk, SOCK_URGINLINE) || !u->oob_skb)
+		return -EINVAL;
+
+	chunk = state->recv_actor(u->oob_skb, 0, chunk, state);
+	if (chunk < 0)
+		return -EFAULT;
+
+	if (!(state->flags & MSG_PEEK)) {
+		UNIXCB(u->oob_skb).consumed += 1;
+		kfree_skb(u->oob_skb);
+		u->oob_skb = NULL;
+	}
+	state->msg->msg_flags |= MSG_OOB;
+	return 1;
+}
+
+static struct sk_buff *manage_oob(struct sk_buff *skb, struct sock *sk,
+				  int flags, int copied)
+{
+	struct unix_sock *u = unix_sk(sk);
+
+	if (!unix_skb_len(skb) && !(flags & MSG_PEEK)) {
+		skb_unlink(skb, &sk->sk_receive_queue);
+		consume_skb(skb);
+		skb = NULL;
+	} else {
+		if (skb == u->oob_skb) {
+			if (copied) {
+				skb = NULL;
+			} else if (sock_flag(sk, SOCK_URGINLINE)) {
+				if (!(flags & MSG_PEEK)) {
+					u->oob_skb = NULL;
+					consume_skb(skb);
+				}
+			} else if (!(flags & MSG_PEEK)) {
+				skb_unlink(skb, &sk->sk_receive_queue);
+				consume_skb(skb);
+				skb = skb_peek(&sk->sk_receive_queue);
+			}
+		}
+	}
+	return skb;
+}
+#endif
+
 static int unix_stream_read_generic(struct unix_stream_read_state *state,
 				    bool freezable)
 {
@@ -2383,6 +2497,15 @@ static int unix_stream_read_generic(struct unix_stream_read_state *state,
 
 	if (unlikely(flags & MSG_OOB)) {
 		err = -EOPNOTSUPP;
+#if IS_ENABLED(CONFIG_AF_UNIX_OOB)
+		mutex_lock(&u->iolock);
+		unix_state_lock(sk);
+
+		err = unix_stream_recv_urg(state);
+
+		unix_state_unlock(sk);
+		mutex_unlock(&u->iolock);
+#endif
 		goto out;
 	}
 
@@ -2411,6 +2534,18 @@ redo:
 		}
 		last = skb = skb_peek(&sk->sk_receive_queue);
 		last_len = last ? last->len : 0;
+
+#if IS_ENABLED(CONFIG_AF_UNIX_OOB)
+		if (skb) {
+			skb = manage_oob(skb, sk, flags, copied);
+			if (!skb) {
+				unix_state_unlock(sk);
+				if (copied)
+					break;
+				goto redo;
+			}
+		}
+#endif
 again:
 		if (skb == NULL) {
 			if (copied >= target)
@@ -2746,6 +2881,20 @@ static int unix_ioctl(struct socket *sock, unsigned int cmd, unsigned long arg)
 	case SIOCUNIXFILE:
 		err = unix_open_file(sk);
 		break;
+#if IS_ENABLED(CONFIG_AF_UNIX_OOB)
+	case SIOCATMARK:
+		{
+			struct sk_buff *skb;
+			struct unix_sock *u = unix_sk(sk);
+			int answ = 0;
+
+			skb = skb_peek(&sk->sk_receive_queue);
+			if (skb && skb == u->oob_skb)
+				answ = 1;
+			err = put_user(answ, (int __user *)arg);
+		}
+		break;
+#endif
 	default:
 		err = -ENOIOCTLCMD;
 		break;