[glib: 2/3] gmodule: Add locking around dlerror() for some libc implementations
- From: Sebastian Dröge <sdroege src gnome org>
- To: commits-list gnome org
- Cc:
- Subject: [glib: 2/3] gmodule: Add locking around dlerror() for some libc implementations
- Date: Fri, 28 May 2021 10:03:00 +0000 (UTC)
commit 483843c282c62ab8c81113578fd8163bcec238e1
Author: Philip Withnall <pwithnall endlessos org>
Date: Thu May 27 13:46:36 2021 +0100
gmodule: Add locking around dlerror() for some libc implementations
Specifically, for uclibc at the moment. Other implementations may need
locking, but I haven’t checked any aside from uclibc-ng and glibc.
POSIX.1-2001 specifies that `dlerror()` is not thread-safe, but the
glibc (and likely other libc) implementation is.
Issue #399 was originally reported about eglibc, but that project has
since died and been merged back into glibc. So that’s one less thing to
worry about.
Signed-off-by: Philip Withnall <pwithnall endlessos org>
Fixes: #399
gmodule/gmodule-dl.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 46 insertions(+), 2 deletions(-)
---
diff --git a/gmodule/gmodule-dl.c b/gmodule/gmodule-dl.c
index 7fb30bd84..0d75e9d31 100644
--- a/gmodule/gmodule-dl.c
+++ b/gmodule/gmodule-dl.c
@@ -28,6 +28,7 @@
#include "config.h"
#include <dlfcn.h>
+#include <glib.h>
/* Perl includes <nlist.h> and <link.h> instead of <dlfcn.h> on some systems? */
@@ -73,7 +74,42 @@
#endif /* RTLD_GLOBAL */
-/* --- functions --- */
+/* According to POSIX.1-2001, dlerror() is not necessarily thread-safe
+ * (see https://pubs.opengroup.org/onlinepubs/009695399/), and so must be
+ * called within the same locked section as the dlopen()/dlsym() call which
+ * may have caused an error.
+ *
+ * However, some libc implementations, such as glibc, implement dlerror() using
+ * thread-local storage, so are thread-safe. As of early 2021:
+ * - glibc is thread-safe: https://github.com/bminor/glibc/blob/master/dlfcn/libc_dlerror_result.c
+ * - uclibc-ng is not thread-safe:
https://cgit.uclibc-ng.org/cgi/cgit/uclibc-ng.git/tree/ldso/libdl/libdl.c?id=132decd2a043d0ccf799f42bf89f3ae0c11e95d5#n1075
+ * - Other libc implementations have not been checked, and no problems have
+ * been reported with them in 10 years, so default to assuming that they
+ * don’t need additional thread-safety from GLib
+ */
+#if defined(__UCLIBC__)
+G_LOCK_DEFINE_STATIC (errors);
+#else
+#define DLERROR_IS_THREADSAFE 1
+#endif
+
+static void
+lock_dlerror (void)
+{
+#ifndef DLERROR_IS_THREADSAFE
+ G_LOCK (errors);
+#endif
+}
+
+static void
+unlock_dlerror (void)
+{
+#ifndef DLERROR_IS_THREADSAFE
+ G_UNLOCK (errors);
+#endif
+}
+
+/* This should be called with lock_dlerror() held */
static const gchar *
fetch_dlerror (gboolean replace_null)
{
@@ -95,10 +131,12 @@ _g_module_open (const gchar *file_name,
{
gpointer handle;
+ lock_dlerror ();
handle = dlopen (file_name,
(bind_local ? 0 : RTLD_GLOBAL) | (bind_lazy ? RTLD_LAZY : RTLD_NOW));
if (!handle)
g_module_set_error (fetch_dlerror (TRUE));
+ unlock_dlerror ();
return handle;
}
@@ -119,6 +157,7 @@ _g_module_self (void)
* always returns 'undefined symbol'. Only if RTLD_DEFAULT or
* NULL is given, dlsym returns an appropriate pointer.
*/
+ lock_dlerror ();
#if defined(__BIONIC__)
handle = RTLD_DEFAULT;
#else
@@ -126,6 +165,7 @@ _g_module_self (void)
#endif
if (!handle)
g_module_set_error (fetch_dlerror (TRUE));
+ unlock_dlerror ();
return handle;
}
@@ -137,8 +177,10 @@ _g_module_close (gpointer handle)
if (handle != RTLD_DEFAULT)
#endif
{
+ lock_dlerror ();
if (dlclose (handle) != 0)
- g_module_set_error (fetch_dlerror (TRUE));
+ g_module_set_error (fetch_dlerror (TRUE));
+ unlock_dlerror ();
}
}
@@ -149,11 +191,13 @@ _g_module_symbol (gpointer handle,
gpointer p;
const gchar *msg;
+ lock_dlerror ();
fetch_dlerror (FALSE);
p = dlsym (handle, symbol_name);
msg = fetch_dlerror (FALSE);
if (msg)
g_module_set_error (msg);
+ unlock_dlerror ();
return p;
}
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