From 2fb4cdcedd8720f78c4bd44739a5d30dd1a7d9a5 Mon Sep 17 00:00:00 2001
From: Alejandro Vallejo <alejandro.vallejo@cloud.com>
Date: Mon, 25 Sep 2023 18:32:24 +0100
Subject: [PATCH 08/11] tools/libfsimage: Export a new function to preload all
 plugins

This is work required in order to let pygrub operate in highly deprivileged
chroot mode. This patch adds a function that preloads every plugin, hence
ensuring that a on function exit, every shared library is loaded in memory.

The new "init" function is supposed to be used before depriv, but that's
fine because it's not acting on untrusted data.

This is part of XSA-443 / CVE-2023-34325

Signed-off-by: Alejandro Vallejo <alejandro.vallejo@cloud.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
 tools/libfsimage/common/fsimage_plugin.c |  4 ++--
 tools/libfsimage/common/mapfile-GNU      |  1 +
 tools/libfsimage/common/mapfile-SunOS    |  1 +
 tools/libfsimage/common/xenfsimage.h     |  8 ++++++++
 tools/pygrub/src/fsimage/fsimage.c       | 15 +++++++++++++++
 5 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/tools/libfsimage/common/fsimage_plugin.c b/tools/libfsimage/common/fsimage_plugin.c
index de1412b4233a..d0cb9e96a654 100644
--- a/tools/libfsimage/common/fsimage_plugin.c
+++ b/tools/libfsimage/common/fsimage_plugin.c
@@ -119,7 +119,7 @@ fail:
 	return (-1);
 }
 
-static int load_plugins(void)
+int fsi_init(void)
 {
 	const char *fsdir = getenv("XEN_FSIMAGE_FSDIR");
 	struct dirent *dp = NULL;
@@ -180,7 +180,7 @@ int find_plugin(fsi_t *fsi, const char *path, const char *options)
 	fsi_plugin_t *fp;
 	int ret = 0;
 
-	if (plugins == NULL && (ret = load_plugins()) != 0)
+	if (plugins == NULL && (ret = fsi_init()) != 0)
 		goto out;
 
 	for (fp = plugins; fp != NULL; fp = fp->fp_next) {
diff --git a/tools/libfsimage/common/mapfile-GNU b/tools/libfsimage/common/mapfile-GNU
index 26d4d7a69ec7..2d54d527d7f5 100644
--- a/tools/libfsimage/common/mapfile-GNU
+++ b/tools/libfsimage/common/mapfile-GNU
@@ -1,6 +1,7 @@
 VERSION {
 	libfsimage.so.1.0 {
 		global:
+			fsi_init;
 			fsi_open_fsimage;
 			fsi_close_fsimage;
 			fsi_file_exists;
diff --git a/tools/libfsimage/common/mapfile-SunOS b/tools/libfsimage/common/mapfile-SunOS
index e99b90b65077..48deedb4252f 100644
--- a/tools/libfsimage/common/mapfile-SunOS
+++ b/tools/libfsimage/common/mapfile-SunOS
@@ -1,5 +1,6 @@
 libfsimage.so.1.0 {
 	global:
+		fsi_init;
 		fsi_open_fsimage;
 		fsi_close_fsimage;
 		fsi_file_exists;
diff --git a/tools/libfsimage/common/xenfsimage.h b/tools/libfsimage/common/xenfsimage.h
index 201abd54f23a..341883b2d71a 100644
--- a/tools/libfsimage/common/xenfsimage.h
+++ b/tools/libfsimage/common/xenfsimage.h
@@ -35,6 +35,14 @@ extern C {
 typedef struct fsi fsi_t;
 typedef struct fsi_file fsi_file_t;
 
+/*
+ * Optional initialization function. If invoked it loads the associated
+ * dynamic libraries for the backends ahead of time. This is required if
+ * the library is to run as part of a highly deprivileged executable, as
+ * the libraries may not be reachable after depriv.
+ */
+int fsi_init(void);
+
 fsi_t *fsi_open_fsimage(const char *, uint64_t, const char *);
 void fsi_close_fsimage(fsi_t *);
 
diff --git a/tools/pygrub/src/fsimage/fsimage.c b/tools/pygrub/src/fsimage/fsimage.c
index 2ebbbe35df92..92fbf2851f01 100644
--- a/tools/pygrub/src/fsimage/fsimage.c
+++ b/tools/pygrub/src/fsimage/fsimage.c
@@ -286,6 +286,15 @@ fsimage_getbootstring(PyObject *o, PyObject *args)
 	return Py_BuildValue("s", bootstring);
 }
 
+static PyObject *
+fsimage_init(PyObject *o, PyObject *args)
+{
+	if (!PyArg_ParseTuple(args, ""))
+		return (NULL);
+
+	return Py_BuildValue("i", fsi_init());
+}
+
 PyDoc_STRVAR(fsimage_open__doc__,
     "open(name, [offset=off]) - Open the given file as a filesystem image.\n"
     "\n"
@@ -297,7 +306,13 @@ PyDoc_STRVAR(fsimage_getbootstring__doc__,
     "getbootstring(fs) - Return the boot string needed for this file system "
     "or NULL if none is needed.\n");
 
+PyDoc_STRVAR(fsimage_init__doc__,
+    "init() - Loads every dynamic library contained in xenfsimage "
+    "into memory so that it can be used in chrooted environments.\n");
+
 static struct PyMethodDef fsimage_module_methods[] = {
+	{ "init", (PyCFunction)fsimage_init,
+	    METH_VARARGS, fsimage_init__doc__ },
 	{ "open", (PyCFunction)fsimage_open,
 	    METH_VARARGS|METH_KEYWORDS, fsimage_open__doc__ },
 	{ "getbootstring", (PyCFunction)fsimage_getbootstring,
-- 
2.42.0