listen, client: enable SO_PASSCRED, get client's uid

Enable authentication over unix sockets.  Store the client's uid in
the client struct.

src/client.c

@@ -72,8 +72,13 @@ struct client {
 	char buffer[CLIENT_MAX_BUFFER_LENGTH];
 	size_t bufferLength;
 	size_t bufferPos;
+
 	int fd;	/* file descriptor; -1 if expired */
 	int permission;
+
+	/** the uid of the client process, or -1 if unknown */
+	int uid;
+
 	time_t lastTime;
 	struct strnode *cmd_list;	/* for when in list mode */
 	struct strnode *cmd_list_tail;	/* for when in list mode */
@@ -147,6 +152,11 @@ int client_is_expired(const struct client *client)
 	return client->fd < 0;
 }
 
+int client_get_uid(const struct client *client)
+{
+	return client->uid;
+}
+
 int client_get_permission(const struct client *client)
 {
 	return client->permission;
@@ -323,7 +333,7 @@ sockaddr_to_tmp_string(const struct sockaddr *addr)
 	return hostname;
 }
 
-void client_new(int fd, const struct sockaddr *addr)
+void client_new(int fd, const struct sockaddr *addr, int uid)
 {
 	struct client *client;
 
@@ -337,6 +347,7 @@ void client_new(int fd, const struct sockaddr *addr)
 	list_add(&client->siblings, &clients);
 	++num_clients;
 	client_init(client, fd);
+	client->uid = uid;
 	SECURE("client %i: opened from %s\n", client->num,
 	       sockaddr_to_tmp_string(addr));
 }

src/client.h

@@ -33,10 +33,16 @@ void client_manager_deinit(void);
 int client_manager_io(void);
 void client_manager_expire(void);
 
-void client_new(int fd, const struct sockaddr *addr);
+void client_new(int fd, const struct sockaddr *addr, int uid);
 
 int client_is_expired(const struct client *client);
 
+/**
+ * returns the uid of the client process, or a negative value if the
+ * uid is unknown
+ */
+int client_get_uid(const struct client *client);
+
 int client_get_permission(const struct client *client);
 
 void client_set_permission(struct client *client, int permission);

src/listen.c

@@ -74,6 +74,7 @@ static int establishListen(int pf, const struct sockaddr *addrp,
 {
 	int sock;
 	int allowReuse = ALLOW_REUSE;
+	int passcred = 1;
 
 	if ((sock = socket(pf, SOCK_STREAM, 0)) < 0)
 		FATAL("socket < 0\n");
@@ -96,6 +97,10 @@ static int establishListen(int pf, const struct sockaddr *addrp,
 	if (listen(sock, 5) < 0)
 		FATAL("problems listen'ing: %s\n", strerror(errno));
 
+#if defined(HAVE_UN) && defined(SO_PASSCRED)
+	setsockopt(sock, SOL_SOCKET, SO_PASSCRED, &passcred, sizeof(passcred));
+#endif
+
 	numberOfListenSockets++;
 	listenSockets =
 	    xrealloc(listenSockets, sizeof(int) * numberOfListenSockets);
@@ -258,6 +263,22 @@ void freeAllListenSockets(void)
 	listenSockets = NULL;
 }
 
+static int get_remote_uid(int fd)
+{
+#if defined(HAVE_UN) && defined(SO_PEERCRED)
+	struct ucred cred;
+	socklen_t len = sizeof (cred);
+
+	if (getsockopt(fd, SOL_SOCKET, SO_PEERCRED, &cred, &len) < 0)
+		return 0;
+
+	return cred.uid;
+#else
+	(void)fd;
+	return -1;
+#endif
+}
+
 void getConnections(fd_set * fds)
 {
 	int i;
@@ -269,7 +290,7 @@ void getConnections(fd_set * fds)
 		if (FD_ISSET(listenSockets[i], fds)) {
 			if ((fd = accept(listenSockets[i], &sockAddr, &socklen))
 			    >= 0) {
-				client_new(fd, &sockAddr);
+				client_new(fd, &sockAddr, get_remote_uid(fd));
 			} else if (fd < 0
 				   && (errno != EAGAIN && errno != EINTR)) {
 				ERROR("Problems accept()'ing\n");