[libvirt] [PATCH 03/14] build: prevent unloading of dlopen'd modules

[Daniel P. Berrangé]

We previously added "-z nodelete" to the build of libvirt.so to prevent
crashes when thread local destructors run which point to a code that
has been dlclose()d:

  commit 384b9a76a5e387f64cfe8f83f4a518bb302e80f7
  Author: Daniel P. Berrangé <berrange at redhat.com>
  Date:   Thu Apr 19 11:42:22 2018 +0100

    driver: prevent unloading of dlopen'd modules

The libvirtd loadable modules can suffer from the same problem if they
were ever unloaded. Fortunately we don't ever call dlclose() on them,
but lets add a second layer of protection by linking them with the
"-z nodelete" flag. While we're doing this, lets add a third layer of
protection by passing RTLD_NODELETE to dlopen().

Signed-off-by: Daniel P. Berrangé <berrange at redhat.com>
---
 src/Makefile.am | 6 +++++-
 src/driver.c    | 7 ++++++-
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/Makefile.am b/src/Makefile.am
index 2f8e5f6908..0d8d380df1 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -51,7 +51,11 @@ AM_LDFLAGS =	$(DRIVER_MODULES_LDFLAGS) \
 		$(CYGWIN_EXTRA_LDFLAGS) \
 		$(MINGW_EXTRA_LDFLAGS) \
 		$(NULL)
-AM_LDFLAGS_MOD = -module -avoid-version $(AM_LDFLAGS)
+AM_LDFLAGS_MOD = \
+	-module \
+	-avoid-version \
+	$(LIBVIRT_NODELETE) \
+	$(AM_LDFLAGS)
 AM_LDFLAGS_MOD_NOUNDEF = $(AM_LDFLAGS_MOD) $(NO_UNDEFINED_LDFLAGS)
 
 POD2MAN = pod2man -c "Virtualization Support" -r "$(PACKAGE)-$(VERSION)"
diff --git a/src/driver.c b/src/driver.c
index 52e1ae345a..7d4c78eaaa 100644
--- a/src/driver.c
+++ b/src/driver.c
@@ -45,6 +45,11 @@ static void *
 virDriverLoadModuleFile(const char *file)
 {
     void *handle = NULL;
+    int flags = RTLD_NOW | RTLD_GLOBAL;
+
+# ifdef RTLD_NODELETE
+    flags |= RTLD_NODELETE;
+# endif
 
     VIR_DEBUG("Load module file '%s'", file);
 
@@ -55,7 +60,7 @@ virDriverLoadModuleFile(const char *file)
 
     virUpdateSelfLastChanged(file);
 
-    if (!(handle = dlopen(file, RTLD_NOW | RTLD_GLOBAL)))
+    if (!(handle = dlopen(file, flags)))
         VIR_ERROR(_("failed to load module %s %s"), file, dlerror());
 
     return handle;
-- 
2.14.3