From 9c54a55ebe7b0d242bd2a06359dcc5b627694dcd Mon Sep 17 00:00:00 2001
From: Daniel P. Berrange <berrange@redhat.com>
Date: Fri, 16 Sep 2011 16:23:36 -0600
Subject: [PATCH] Prevent crash from dlclose() of libvirt.so
To: libvir-list@redhat.com

https://bugzilla.redhat.com/show_bug.cgi?id=735127

When libvirt calls virInitialize it creates a thread local
for the virErrorPtr storage, and registers a callback to
cleanup memory when a thread exits. When libvirt is dlclose()d
or otherwise made non-resident, the callback function is
removed from memory, but the thread local may still exist
and if a thread later exists, it will invoke the callback
and SEGV. There may also be other thread locals with callbacks
pointing to libvirt code, so it is in general never safe to
unload libvirt.so from memory once initialized.

To allow dlclose() to succeed, but keep libvirt.so resident
in memory, link with '-z nodelete'. This issue was first
found with the libvirt CIM provider, but can potentially
hit many of the dynamic language bindings which all ultimately
involve dlopen() in some way, either on libvirt.so itself,
or on the glue code for the binding which in turns links
to libvirt

* configure.ac, src/Makefile.am: Ensure libvirt.so is linked
  with -z nodelete
* cfg.mk, .gitignore, tests/Makefile.am, tests/shunloadhelper.c,
  tests/shunloadtest.c: A test case to unload libvirt while
  a thread is still running.
(cherry picked from commit 8e44e5593eb9b89fbc0b54fde15f130707a0d81e)

Conflicts:

	.gitignore - lots of upstream divergence
	cfg.mk - exemptions are stored in .x-sc_avoid_write instead
	src/Makefile.am - some upstream divergence
	tests/Makefile.am - some upstream divergence

Signed-off-by: Daniel Veillard <veillard@redhat.com>
---
 .gitignore             |    3 +
 .x-sc_avoid_write      |    1 +
 configure.ac           |    9 +++
 src/Makefile.am        |    1 +
 tests/Makefile.am      |   14 ++++-
 tests/shunloadhelper.c |   52 ++++++++++++++++
 tests/shunloadtest.c   |  153 ++++++++++++++++++++++++++++++++++++++++++++++++
 7 files changed, 232 insertions(+), 1 deletions(-)
 create mode 100644 tests/shunloadhelper.c
 create mode 100644 tests/shunloadtest.c

diff --git a/.x-sc_avoid_write b/.x-sc_avoid_write
index 1f893b8..e7066d0 100644
--- a/.x-sc_avoid_write
+++ b/.x-sc_avoid_write
@@ -5,3 +5,4 @@
 ^src/xen/xend_internal\.c$
 ^daemon/libvirtd.c$
 ^gnulib/
+^tests/shunloadtest\.c$
diff --git a/configure.ac b/configure.ac
index f30c5e0..eec83bf 100644
--- a/configure.ac
+++ b/configure.ac
@@ -66,9 +66,18 @@ AM_PROG_LIBTOOL
 AM_PROG_CC_C_O
 AM_PROG_LD
 
+AC_MSG_CHECKING([for how to mark DSO non-deletable at runtime])
+LIBVIRT_NODELETE=
+`$LD --help 2>&1 | grep -- "-z nodelete" >/dev/null` && \
+    LIBVIRT_NODELETE="-Wl,-z -Wl,nodelete"
+AC_MSG_RESULT([$LIBVIRT_NODELETE])
+AC_SUBST([LIBVIRT_NODELETE])
+
+AC_MSG_CHECKING([for how to set DSO symbol versions])
 VERSION_SCRIPT_FLAGS=-Wl,--version-script=
 `$LD --help 2>&1 | grep -- --version-script >/dev/null` || \
     VERSION_SCRIPT_FLAGS="-Wl,-M -Wl,"
+AC_MSG_RESULT([$VERSION_SCRIPT_FLAGS])
 
 LIBVIRT_COMPILE_WARNINGS([maximum])
 
diff --git a/src/Makefile.am b/src/Makefile.am
index f8f1354..2d878b0 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -1017,6 +1017,7 @@ libvirt_la_SOURCES =
 libvirt_la_LDFLAGS = $(VERSION_SCRIPT_FLAGS)$(LIBVIRT_SYMBOL_FILE) \
                      -version-info $(LIBVIRT_VERSION_INFO) \
                     $(COVERAGE_CFLAGS:-f%=-Wc,-f%) \
+		    $(LIBVIRT_NODELETE) \
 		    $(CYGWIN_EXTRA_LDFLAGS) $(MINGW_EXTRA_LDFLAGS)
 libvirt_la_BUILT_LIBADD += ../gnulib/lib/libgnu.la
 libvirt_la_LIBADD += $(LIBXML_LIBS) \
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 81a660e..57cf6f4 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -72,7 +72,9 @@ EXTRA_DIST =		\
 	qemuhelpdata
 
 noinst_PROGRAMS = virshtest conftest \
-        nodeinfotest statstest qparamtest virbuftest
+        nodeinfotest statstest qparamtest virbuftest shunloadtest
+
+check_LTLIBRARIES = libshunload.la
 
 if WITH_XEN
 noinst_PROGRAMS += xml2sexprtest sexpr2xmltest \
@@ -151,6 +153,7 @@ TESTS = virshtest \
 	statstest \
 	qparamtest \
 	virbuftest \
+	shunloadtest \
 	$(test_scripts)
 
 if WITH_XEN
@@ -362,6 +365,15 @@ eventtest_SOURCES = \
 eventtest_LDADD = -lrt $(LDADDS)
 endif
 
+libshunload_la_SOURCES = shunloadhelper.c
+libshunload_la_LIBADD = ../src/libvirt.la
+libshunload_la_LDFLAGS = -module -avoid-version -rpath /evil/libtool/hack/to/force/shared/lib/creation
+
+shunloadtest_SOURCES = \
+	shunloadtest.c
+shunloadtest_LDADD = -lpthread -ldl
+shunloadtest_DEPENDENCIES = libshunload.la
+
 if WITH_CIL
 CILOPTFLAGS =
 CILOPTINCS =
diff --git a/tests/shunloadhelper.c b/tests/shunloadhelper.c
new file mode 100644
index 0000000..efd8af0
--- /dev/null
+++ b/tests/shunloadhelper.c
@@ -0,0 +1,52 @@
+/*
+ * Copyright (C) 2011 Red Hat, Inc.
+ *
+ * This library 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; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library 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.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307  USA
+ *
+ */
+
+/*
+ * This is a helper for shunloadtest.c. This function is built into
+ * a shared library and linked with libvirto.so
+ *
+ * The function initializes libvirt and primes the thread local with
+ * an error which needs to be freed at thread exit
+ */
+
+#include <config.h>
+#include "internal.h"
+
+#include <libvirt/libvirt.h>
+#include <libvirt/virterror.h>
+#include <stdlib.h>
+
+static void shunloadError(void *userData ATTRIBUTE_UNUSED,
+                          virErrorPtr error ATTRIBUTE_UNUSED)
+{
+}
+
+void shunloadStart(void);
+
+void shunloadStart(void) {
+    virConnectPtr conn;
+
+    virSetErrorFunc(NULL, shunloadError);
+    virInitialize();
+
+    conn = virConnectOpen("test:///default");
+    virDomainDestroy(NULL);
+    if (conn)
+        virConnectClose(conn);
+}
diff --git a/tests/shunloadtest.c b/tests/shunloadtest.c
new file mode 100644
index 0000000..2cdb8b8
--- /dev/null
+++ b/tests/shunloadtest.c
@@ -0,0 +1,153 @@
+/*
+ * Copyright (C) 2011 Red Hat, Inc.
+ *
+ * This library 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; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library 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.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307  USA
+ *
+ */
+
+/*
+ * When libvirt initializes, it creates a thread local for storing
+ * the last virErrorPtr instance. It also registers a cleanup
+ * callback for the thread local that will be invoked whenever
+ * a thread exits.
+ *
+ * If the libvirt.so library was dlopen()'d and is dlclose()'d
+ * while there is still a thread present, then when that thread
+ * later exits, the libvirt cleanup callback will be invoked.
+ * Unfortunately libvirt.so will no longer be in memory so the
+ * callback SEGVs (if you're lucky), or invokes unlreated
+ * code at the same address as the old callback (if you're
+ * unlucky).
+ *
+ * To fix the problem libvirt is linked '-z nodelete' which
+ * prevents the code being removed from memory at dlclose().
+ *
+ * This test case demonstrates this SEGV scenario. If this
+ * test does not SEGV, then the '-z nodelete' fix is working
+ */
+
+#include <config.h>
+
+#ifdef linux
+
+# include <dlfcn.h>
+# include <pthread.h>
+# include <stdbool.h>
+# include <stdio.h>
+# include <unistd.h>
+# include <signal.h>
+
+# include "internal.h"
+# include "ignore-value.h"
+# include "testutils.h"
+
+pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
+pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
+bool running = false;
+bool quit = false;
+
+static void *threadMain(void *arg)
+{
+    void (*startup)(void) = arg;
+
+    startup();
+
+    pthread_mutex_lock(&lock);
+    running = true;
+    pthread_cond_signal(&cond);
+
+    while (!quit) {
+        pthread_cond_wait(&cond, &lock);
+    }
+    pthread_mutex_unlock(&lock);
+
+    return NULL;
+}
+
+static void sigHandler(int sig)
+{
+    ignore_value(write(STDERR_FILENO, "FAIL\n", 5));
+    signal(sig, SIG_DFL);
+    raise(sig);
+}
+
+/* We're not using the testutils.c main() wrapper because
+ * we don't want  'shunloadtest' itself to link against
+ * libvirt.so. We need to test dlopen()'ing of libvirt.so
+ */
+int main(int argc ATTRIBUTE_UNUSED, char **argv)
+{
+    void (*startup)(void);
+    pthread_t t;
+    void *lib;
+    char *theprogname;
+
+    theprogname = argv[0];
+    if (STRPREFIX(theprogname, "./"))
+        theprogname += 2;
+
+    fprintf(stderr, "TEST: %s\n", theprogname);
+    fprintf(stderr, "      .%*s 1   ", 39, "");
+    signal(SIGSEGV, sigHandler);
+
+    if (!(lib = dlopen("./.libs/libshunload.so", RTLD_NOW))) {
+        fprintf(stderr, "Cannot load ./.libs/libshunload.so %s\n", dlerror());
+        return 1;
+    }
+    if (!(startup = dlsym(lib, "shunloadStart"))) {
+        fprintf(stderr, "Cannot find shunloadStart %s\n", dlerror());
+        return 1;
+    }
+
+    /*
+     * Create a thread which is going to initialize libvirt
+     * and raise an error
+     */
+    pthread_create(&t, NULL, threadMain, startup);
+
+    /* Wait for the thread to start and call libvirt */
+    pthread_mutex_lock(&lock);
+    while (!running) {
+        pthread_cond_wait(&cond, &lock);
+    }
+
+    /* Close the shared library (and thus make libvirt.so
+     * non-resident */
+    dlclose(lib);
+
+    /* Tell the thread to quit */
+    quit = true;
+    pthread_cond_signal(&cond);
+    pthread_mutex_unlock(&lock);
+
+    pthread_join(t, NULL);
+
+    /* If we got to here the thread successfully exited without
+     * causing a SEGV !
+     */
+
+    fprintf(stderr, "OK\n");
+
+    return 0;
+}
+
+#else
+
+int main(void)
+{
+    return EXIT_AM_SKIP;
+}
+
+#endif
-- 
1.7.4.4