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gmodule: Add locking around dlerror() for some libc implementations

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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
This commit is contained in:
Philip Withnall 2021-05-27 13:46:36 +01:00
parent 73a78f7470
commit 483843c282
1 changed files with 46 additions and 2 deletions
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48
gmodule/gmodule-dl.c
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@ -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;
}