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Merge branch '399-dlerror-thread-safety' into 'master'

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

Closes #399

See merge request GNOME/glib!2122
This commit is contained in:
Sebastian Dröge 2021-05-28 10:02:59 +00:00
commit 0d7f3e74e0
1 changed files with 49 additions and 5 deletions
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54
gmodule/gmodule-dl.c
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@ -28,6 +28,7 @@
#include "config.h" #include "config.h"
#include <dlfcn.h> #include <dlfcn.h>
#include <glib.h>
/* Perl includes <nlist.h> and <link.h> instead of <dlfcn.h> on some systems? */ /* Perl includes <nlist.h> and <link.h> instead of <dlfcn.h> on some systems? */
@ -73,11 +74,46 @@
#endif /* RTLD_GLOBAL */ #endif /* RTLD_GLOBAL */
/* --- functions --- */ /* According to POSIX.1-2001, dlerror() is not necessarily thread-safe
static gchar* * (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) fetch_dlerror (gboolean replace_null)
{ {
gchar *msg = dlerror (); const gchar *msg = dlerror ();
/* make sure we always return an error message != NULL, if /* make sure we always return an error message != NULL, if
* expected to do so. */ * expected to do so. */
@ -95,10 +131,12 @@ _g_module_open (const gchar *file_name,
{ {
gpointer handle; gpointer handle;
lock_dlerror ();
handle = dlopen (file_name, handle = dlopen (file_name,
(bind_local ? 0 : RTLD_GLOBAL) | (bind_lazy ? RTLD_LAZY : RTLD_NOW)); (bind_local ? 0 : RTLD_GLOBAL) | (bind_lazy ? RTLD_LAZY : RTLD_NOW));
if (!handle) if (!handle)
g_module_set_error (fetch_dlerror (TRUE)); g_module_set_error (fetch_dlerror (TRUE));
unlock_dlerror ();
return handle; return handle;
} }
@ -119,6 +157,7 @@ _g_module_self (void)
* always returns 'undefined symbol'. Only if RTLD_DEFAULT or * always returns 'undefined symbol'. Only if RTLD_DEFAULT or
* NULL is given, dlsym returns an appropriate pointer. * NULL is given, dlsym returns an appropriate pointer.
*/ */
lock_dlerror ();
#if defined(__BIONIC__) #if defined(__BIONIC__)
handle = RTLD_DEFAULT; handle = RTLD_DEFAULT;
#else #else
@ -126,6 +165,7 @@ _g_module_self (void)
#endif #endif
if (!handle) if (!handle)
g_module_set_error (fetch_dlerror (TRUE)); g_module_set_error (fetch_dlerror (TRUE));
unlock_dlerror ();
return handle; return handle;
} }
@ -137,8 +177,10 @@ _g_module_close (gpointer handle)
if (handle != RTLD_DEFAULT) if (handle != RTLD_DEFAULT)
#endif #endif
{ {
lock_dlerror ();
if (dlclose (handle) != 0) if (dlclose (handle) != 0)
g_module_set_error (fetch_dlerror (TRUE)); g_module_set_error (fetch_dlerror (TRUE));
unlock_dlerror ();
} }
} }
@ -147,13 +189,15 @@ _g_module_symbol (gpointer handle,
const gchar *symbol_name) const gchar *symbol_name)
{ {
gpointer p; gpointer p;
gchar *msg; const gchar *msg;
lock_dlerror ();
fetch_dlerror (FALSE); fetch_dlerror (FALSE);
p = dlsym (handle, symbol_name); p = dlsym (handle, symbol_name);
msg = fetch_dlerror (FALSE); msg = fetch_dlerror (FALSE);
if (msg) if (msg)
g_module_set_error (msg); g_module_set_error (msg);
unlock_dlerror ();
return p; return p;
} }