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ld.so: Examine GLRO to detect inactive loader [BZ #20204]

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GLRO (_rtld_global_ro) is read-only after initialization and can
therefore not be patched at run time, unlike the hook table addresses
and their contents, so this is a desirable hardening feature.

The hooks are only needed if ld.so has not been initialized, and this
happens only after static dlopen (dlmopen uses a single ld.so object
across all namespaces).

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
This commit is contained in:
Florian Weimer 2017-12-18 20:04:13 +01:00
parent 49b036bce9
commit 8e1472d2c1
15 changed files with 61 additions and 16 deletions
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22
ChangeLog
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@ -1,3 +1,25 @@
2017-12-18 Florian Weimer <fweimer@redhat.com>
[BZ #20204]
ld.so: Harden dl-libc/libdl hooks.
* sysdeps/generic/ldsodefs.h (_dl_init_all_dirs): Update comment.
(rtld_active): New function.
* dlfcn/dladdr.c (__dladdr): Call it.
* dlfcn/dladdr1.c (__dladdr1): Likewise.
* dlfcn/dlclose.c (__dlcose): Likewise.
* dlfcn/dlerror.c (__dlerror): Likewise.
* dlfcn/dlinfo.c (__dlinfo): Likewise.
* dlfcn/dlmopen.c (__dlmopen): Likewise.
* dlfcn/dlopen.c (__dlopen): Likewise.
* dlfcn/dlopenold.c (__dlopen_nocheck): Likewise.
* dlfcn/dlsym.c (__dlsym): Likewise.
* dlfcn/dlvsym.c (__dlvsym): Likewise.
* libio/vtables.c (_IO_vtable_check): Likewise.
* elf/dl-libc.c (__libc_dlopen_mode, __libc_dlsym)
(__libc_dlclose): Likewise.
* elf/rtld.c (dl_main): Update comment on the _dl_init_all_dirs
assignment.
2017-12-18 Joseph Myers <joseph@codesourcery.com>
[BZ #22446]

3
dlfcn/dladdr.c
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@ -17,6 +17,7 @@
<http://www.gnu.org/licenses/>. */
#include <dlfcn.h>
#include <ldsodefs.h>
#if !defined SHARED && IS_IN (libdl)
@ -32,7 +33,7 @@ int
__dladdr (const void *address, Dl_info *info)
{
# ifdef SHARED
if (__glibc_unlikely (_dlfcn_hook != NULL))
if (!rtld_active ())
return _dlfcn_hook->dladdr (address, info);
# endif
return _dl_addr (address, info, NULL, NULL);

3
dlfcn/dladdr1.c
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@ -17,6 +17,7 @@
<http://www.gnu.org/licenses/>. */
#include <dlfcn.h>
#include <ldsodefs.h>
#if !defined SHARED && IS_IN (libdl)
@ -32,7 +33,7 @@ int
__dladdr1 (const void *address, Dl_info *info, void **extra, int flags)
{
# ifdef SHARED
if (__glibc_unlikely (_dlfcn_hook != NULL))
if (!rtld_active ())
return _dlfcn_hook->dladdr1 (address, info, extra, flags);
# endif

2
dlfcn/dlclose.c
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@ -39,7 +39,7 @@ int
__dlclose (void *handle)
{
# ifdef SHARED
if (__glibc_unlikely (_dlfcn_hook != NULL))
if (!rtld_active ())
return _dlfcn_hook->dlclose (handle);
# endif

2
dlfcn/dlerror.c
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@ -63,7 +63,7 @@ __dlerror (void)
struct dl_action_result *result;
# ifdef SHARED
if (__glibc_unlikely (_dlfcn_hook != NULL))
if (!rtld_active ())
return _dlfcn_hook->dlerror ();
# endif

2
dlfcn/dlinfo.c
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@ -111,7 +111,7 @@ int
__dlinfo (void *handle, int request, void *arg DL_CALLER_DECL)
{
# ifdef SHARED
if (__glibc_unlikely (_dlfcn_hook != NULL))
if (!rtld_active ())
return _dlfcn_hook->dlinfo (handle, request, arg,
DL_CALLER);
# endif

2
dlfcn/dlmopen.c
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@ -79,7 +79,7 @@ void *
__dlmopen (Lmid_t nsid, const char *file, int mode DL_CALLER_DECL)
{
# ifdef SHARED
if (__glibc_unlikely (_dlfcn_hook != NULL))
if (!rtld_active ())
return _dlfcn_hook->dlmopen (nsid, file, mode, RETURN_ADDRESS (0));
# endif

2
dlfcn/dlopen.c
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@ -74,7 +74,7 @@ void *
__dlopen (const char *file, int mode DL_CALLER_DECL)
{
# ifdef SHARED
if (__glibc_unlikely (_dlfcn_hook != NULL))
if (!rtld_active ())
return _dlfcn_hook->dlopen (file, mode, DL_CALLER);
# endif

2
dlfcn/dlopenold.c
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@ -70,7 +70,7 @@ __dlopen_nocheck (const char *file, int mode)
mode |= RTLD_LAZY;
args.mode = mode;
if (__glibc_unlikely (_dlfcn_hook != NULL))
if (!rtld_active ())
return _dlfcn_hook->dlopen (file, mode, RETURN_ADDRESS (0));
return _dlerror_run (dlopen_doit, &args) ? NULL : args.new;

2
dlfcn/dlsym.c
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@ -55,7 +55,7 @@ void *
__dlsym (void *handle, const char *name DL_CALLER_DECL)
{
# ifdef SHARED
if (__glibc_unlikely (_dlfcn_hook != NULL))
if (!rtld_active ())
return _dlfcn_hook->dlsym (handle, name, DL_CALLER);
# endif

2
dlfcn/dlvsym.c
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@ -58,7 +58,7 @@ __dlvsym (void *handle, const char *name, const char *version_str
DL_CALLER_DECL)
{
# ifdef SHARED
if (__glibc_unlikely (_dlfcn_hook != NULL))
if (!rtld_active ())
return _dlfcn_hook->dlvsym (handle, name, version_str, DL_CALLER);
# endif

6
elf/dl-libc.c
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@ -157,7 +157,7 @@ __libc_dlopen_mode (const char *name, int mode)
args.caller_dlopen = RETURN_ADDRESS (0);
#ifdef SHARED
if (__glibc_unlikely (_dl_open_hook != NULL))
if (!rtld_active ())
return _dl_open_hook->dlopen_mode (name, mode);
return (dlerror_run (do_dlopen, &args) ? NULL : (void *) args.map);
#else
@ -203,7 +203,7 @@ __libc_dlsym (void *map, const char *name)
args.name = name;
#ifdef SHARED
if (__glibc_unlikely (_dl_open_hook != NULL))
if (!rtld_active ())
return _dl_open_hook->dlsym (map, name);
#endif
return (dlerror_run (do_dlsym, &args) ? NULL
@ -215,7 +215,7 @@ int
__libc_dlclose (void *map)
{
#ifdef SHARED
if (__glibc_unlikely (_dl_open_hook != NULL))
if (!rtld_active ())
return _dl_open_hook->dlclose (map);
#endif
return dlerror_run (do_dlclose, map);

4
elf/rtld.c
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@ -2096,7 +2096,9 @@ ERROR: ld.so: object '%s' cannot be loaded as audit interface: %s; ignored.\n",
GLRO(dl_initial_searchlist) = *GL(dl_ns)[LM_ID_BASE]._ns_main_searchlist;
/* Remember the last search directory added at startup, now that
malloc will no longer be the one from dl-minimal.c. */
malloc will no longer be the one from dl-minimal.c. As a side
effect, this marks ld.so as initialized, so that the rtld_active
function returns true from now on. */
GLRO(dl_init_all_dirs) = GL(dl_all_dirs);
/* Print scope information. */

3
libio/vtables.c
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@ -19,6 +19,7 @@
#include <dlfcn.h>
#include <libioP.h>
#include <stdio.h>
#include <ldsodefs.h>
#ifdef SHARED
@ -54,7 +55,7 @@ _IO_vtable_check (void)
{
Dl_info di;
struct link_map *l;
if (_dl_open_hook != NULL
if (!rtld_active ()
|| (_dl_addr (_IO_vtable_check, &di, &l, NULL) != 0
&& l->l_ns != LM_ID_BASE))
return;

20
sysdeps/generic/ldsodefs.h
View File

@ -558,7 +558,11 @@ struct rtld_global_ro
/* Map of shared object to be prelink traced. */
EXTERN struct link_map *_dl_trace_prelink_map;
/* All search directories defined at startup. */
/* All search directories defined at startup. This is assigned a
non-NULL pointer by the ld.so startup code (after initialization
to NULL), so this can also serve as an indicator whether a copy
of ld.so is initialized and active. See the rtld_active function
below. */
EXTERN struct r_search_path_elem *_dl_init_all_dirs;
#ifdef NEED_DL_SYSINFO
@ -1144,6 +1148,20 @@ extern void _dl_non_dynamic_init (void)
extern void _dl_aux_init (ElfW(auxv_t) *av)
attribute_hidden;
/* Return true if the ld.so copy in this namespace is actually active
and working. If false, the dl_open/dlfcn hooks have to be used to
call into the outer dynamic linker (which happens after static
dlopen). */
#ifdef SHARED
static inline bool
rtld_active (void)
{
/* The default-initialized variable does not have a non-zero
dl_init_all_dirs member, so this allows us to recognize an
initialized and active ld.so copy. */
return GLRO(dl_init_all_dirs) != NULL;
}
#endif
__END_DECLS