unix_diag: Unix peer inode NLA

Report the peer socket inode ID as NLA. With this it's finally
possible to find out the other end of an interesting unix connection.
Signed-off-by: NPavel Emelyanov <xemul@parallels.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/unix_diag.h

@@ -13,6 +13,7 @@ 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 */
 
 struct unix_diag_msg {
 	__u8	udiag_family;
@@ -27,6 +28,7 @@ struct unix_diag_msg {
 enum {
 	UNIX_DIAG_NAME,
 	UNIX_DIAG_VFS,
+	UNIX_DIAG_PEER,
 
 	UNIX_DIAG_MAX,
 };

net/unix/diag.c

@@ -43,6 +43,26 @@ static int sk_diag_dump_vfs(struct sock *sk, struct sk_buff *nlskb)
 	return -EMSGSIZE;
 }
 
+static int sk_diag_dump_peer(struct sock *sk, struct sk_buff *nlskb)
+{
+	struct sock *peer;
+	int ino;
+
+	peer = unix_peer_get(sk);
+	if (peer) {
+		unix_state_lock(peer);
+		ino = sock_i_ino(peer);
+		unix_state_unlock(peer);
+		sock_put(peer);
+
+		RTA_PUT_U32(nlskb, UNIX_DIAG_PEER, ino);
+	}
+
+	return 0;
+rtattr_failure:
+	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)
 {
@@ -69,6 +89,10 @@ static int sk_diag_fill(struct sock *sk, struct sk_buff *skb, struct unix_diag_r
 			sk_diag_dump_vfs(sk, skb))
 		goto nlmsg_failure;
 
+	if ((req->udiag_show & UDIAG_SHOW_PEER) &&
+			sk_diag_dump_peer(sk, skb))
+		goto nlmsg_failure;
+
 	nlh->nlmsg_len = skb_tail_pointer(skb) - b;
 	return skb->len;