check for overlong unix socket paths

In pcu_l1if_open(), use osmo_strlcpy() instead of strncpy() and check for
overflow. This catches overlong and non-NUL-terminated socket paths.

Change-Id: I825190cbb34d052b797e9fb5208884d6f5992839
Related: OS#2673
diff --git a/src/osmobts_sock.cpp b/src/osmobts_sock.cpp
index 477521d..6b49347 100644
--- a/src/osmobts_sock.cpp
+++ b/src/osmobts_sock.cpp
@@ -265,8 +265,11 @@
 	}
 
 	local.sun_family = AF_UNIX;
-	strncpy(local.sun_path, bts->pcu_sock_path, sizeof(local.sun_path));
-	local.sun_path[sizeof(local.sun_path) - 1] = '\0';
+	if (osmo_strlcpy(local.sun_path, bts->pcu_sock_path, sizeof(local.sun_path)) >= sizeof(local.sun_path)) {
+		LOGP(DLGLOBAL, LOGL_ERROR, "Socket path exceeds maximum length of %zd bytes: %s\n",
+		     sizeof(local.sun_path), bts->pcu_sock_path);
+		return -ENOSPC;
+	}
 
 	/* we use the same magic that X11 uses in Xtranssock.c for
 	 * calculating the proper length of the sockaddr */