[PATCH v2] libs/light: make it build without setresuid()

[Manuel Bouyer <bouyer@netbsd.org>]

NetBSD doesn't have setresuid(). introcuce libxl__setresuid(),
which on NetBSD assert() that it's never called (it should not be called when
dm restriction is off, and NetBSD doesn't support dm restriction at
this time).
On linux and FreeBSD it just calls setresuid().

Signed-off-by: Manuel Bouyer <bouyer@netbsd.org>
---
 tools/libs/light/Makefile          |  4 ++--
 tools/libs/light/libxl_dm.c        |  2 +-
 tools/libs/light/libxl_internal.h  |  3 +++
 tools/libs/light/libxl_netbsd.c    |  5 +++++
 tools/libs/light/libxl_setresuid.c | 23 +++++++++++++++++++++++
 5 files changed, 34 insertions(+), 3 deletions(-)
 create mode 100644 tools/libs/light/libxl_setresuid.c

diff --git a/tools/libs/light/Makefile b/tools/libs/light/Makefile
index 68f6fa315f..d62ca6e477 100644
--- a/tools/libs/light/Makefile
+++ b/tools/libs/light/Makefile
@@ -64,8 +64,8 @@ SRCS-$(CONFIG_ARM) += libxl_arm_no_acpi.c
 endif
 
 SRCS-OS-$(CONFIG_NetBSD) = libxl_netbsd.c
-SRCS-OS-$(CONFIG_Linux) = libxl_linux.c
-SRCS-OS-$(CONFIG_FreeBSD) = libxl_freebsd.c
+SRCS-OS-$(CONFIG_Linux) = libxl_linux.c libxl_setresuid.c
+SRCS-OS-$(CONFIG_FreeBSD) = libxl_freebsd.c libxl_setresuid.c
 ifeq ($(SRCS-OS-y),)
 $(error Your Operating System is not supported by libxenlight, \
 please check libxl_linux.c and libxl_netbsd.c to see how to get it ported)
diff --git a/tools/libs/light/libxl_dm.c b/tools/libs/light/libxl_dm.c
index 13f79ec471..291dee9b3f 100644
--- a/tools/libs/light/libxl_dm.c
+++ b/tools/libs/light/libxl_dm.c
@@ -3655,7 +3655,7 @@ static int kill_device_model_uid_child(libxl__destroy_devicemodel_state *ddms,
 
     LOGD(DEBUG, domid, "DM reaper: calling setresuid(%d, %d, 0)",
          reaper_uid, dm_kill_uid);
-    r = setresuid(reaper_uid, dm_kill_uid, 0);
+    r = libxl__setresuid(reaper_uid, dm_kill_uid, 0);
     if (r) {
         LOGED(ERROR, domid, "setresuid to (%d, %d, 0)",
               reaper_uid, dm_kill_uid);
diff --git a/tools/libs/light/libxl_internal.h b/tools/libs/light/libxl_internal.h
index 6c8b7d71a9..028bc013d9 100644
--- a/tools/libs/light/libxl_internal.h
+++ b/tools/libs/light/libxl_internal.h
@@ -4845,6 +4845,9 @@ _hidden int libxl__domain_pvcontrol(libxl__egc *egc,
 /* Check whether a domid is recent */
 int libxl__is_domid_recent(libxl__gc *gc, uint32_t domid, bool *recent);
 
+/* os-specific implementation of setresuid() */
+int libxl__setresuid(uid_t ruid, uid_t euid, uid_t suid);
+
 #endif
 
 /*
diff --git a/tools/libs/light/libxl_netbsd.c b/tools/libs/light/libxl_netbsd.c
index 6ad4ed34c2..67caafab9e 100644
--- a/tools/libs/light/libxl_netbsd.c
+++ b/tools/libs/light/libxl_netbsd.c
@@ -124,3 +124,8 @@ int libxl__local_dm_preexec_restrict(libxl__gc *gc)
 {
     return 0;
 }
+
+int libxl__setresuid(uid_t ruid, uid_t euid, uid_t suid)
+{
+    assert(!"setresuid is not available on NetBSD, and dm restrction is not supported, so this code path should not have been reached");
+}
diff --git a/tools/libs/light/libxl_setresuid.c b/tools/libs/light/libxl_setresuid.c
new file mode 100644
index 0000000000..ac5cb5db53
--- /dev/null
+++ b/tools/libs/light/libxl_setresuid.c
@@ -0,0 +1,23 @@
+/*
+ * Copyright (C) 2021
+ * Author Manuel Bouyer <bouyer@netbsd.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation; version 2.1 only. with the special
+ * exception on linking described in file LICENSE.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ */
+ 
+#include "libxl_osdeps.h" /* must come before any other headers */
+
+#include "libxl_internal.h"
+
+int libxl__setresuid(uid_t ruid, uid_t euid, uid_t suid)
+{
+    setresuid(ruid, euid, suid);
+}
-- 
2.29.2