unix_diag: Pending connections IDs NLA

When establishing a unix connection on stream sockets the
server end receives an skb with socket in its receive queue.

Report who is waiting for these ends to be accepted for
listening sockets via NLA.

There's a lokcing issue with this -- the unix sk state lock is
required to access the peer, and it is taken under the listening
sk's queue lock. Strictly speaking the queue lock should be taken
inside the state lock, but since in this case these two sockets
are different it shouldn't lead to deadlock.
Signed-off-by: NPavel Emelyanov <xemul@parallels.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/unix_diag.h

@@ -14,6 +14,7 @@ struct unix_diag_req {
 #define UDIAG_SHOW_NAME		0x00000001	/* show name (not path) */
 #define UDIAG_SHOW_VFS		0x00000002	/* show VFS inode info */
 #define UDIAG_SHOW_PEER		0x00000004	/* show peer socket info */
+#define UDIAG_SHOW_ICONS	0x00000008	/* show pending connections */
 
 struct unix_diag_msg {
 	__u8	udiag_family;
@@ -29,6 +30,7 @@ enum {
 	UNIX_DIAG_NAME,
 	UNIX_DIAG_VFS,
 	UNIX_DIAG_PEER,
+	UNIX_DIAG_ICONS,
 
 	UNIX_DIAG_MAX,
 };

net/unix/diag.c

@@ -63,6 +63,41 @@ static int sk_diag_dump_peer(struct sock *sk, struct sk_buff *nlskb)
 	return -EMSGSIZE;
 }
 
+static int sk_diag_dump_icons(struct sock *sk, struct sk_buff *nlskb)
+{
+	struct sk_buff *skb;
+	u32 *buf;
+	int i;
+
+	if (sk->sk_state == TCP_LISTEN) {
+		spin_lock(&sk->sk_receive_queue.lock);
+		buf = UNIX_DIAG_PUT(nlskb, UNIX_DIAG_ICONS, sk->sk_receive_queue.qlen);
+		i = 0;
+		skb_queue_walk(&sk->sk_receive_queue, skb) {
+			struct sock *req, *peer;
+
+			req = skb->sk;
+			/*
+			 * The state lock is outer for the same sk's
+			 * queue lock. With the other's queue locked it's
+			 * OK to lock the state.
+			 */
+			unix_state_lock_nested(req);
+			peer = unix_sk(req)->peer;
+			if (peer)
+				buf[i++] = sock_i_ino(peer);
+			unix_state_unlock(req);
+		}
+		spin_unlock(&sk->sk_receive_queue.lock);
+	}
+
+	return 0;
+
+rtattr_failure:
+	spin_unlock(&sk->sk_receive_queue.lock);
+	return -EMSGSIZE;
+}
+
 static int sk_diag_fill(struct sock *sk, struct sk_buff *skb, struct unix_diag_req *req,
 		u32 pid, u32 seq, u32 flags, int sk_ino)
 {
@@ -93,6 +128,10 @@ static int sk_diag_fill(struct sock *sk, struct sk_buff *skb, struct unix_diag_r
 			sk_diag_dump_peer(sk, skb))
 		goto nlmsg_failure;
 
+	if ((req->udiag_show & UDIAG_SHOW_ICONS) &&
+			sk_diag_dump_icons(sk, skb))
+		goto nlmsg_failure;
+
 	nlh->nlmsg_len = skb_tail_pointer(skb) - b;
 	return skb->len;