[PATCH] ld.so: Examine GLRO to detect inactive loader [BZ #20204]
Florian Weimer
fweimer@redhat.com
Mon Dec 18 12:34:00 GMT 2017
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).
2017-12-18 Florian Weimer <fweimer@redhat.com>
[BZ #20204]
ld.so: Harden dl-libc/libdl hooks.
* sysdeps/generic/ldsodefs.h (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.
* elf/dl-libc.c (__libc_dlopen_mode, __libc_dlsym)
(__libc_dlclose): Likewise.
diff --git a/dlfcn/dladdr.c b/dlfcn/dladdr.c
index 1753434160..1bebd00240 100644
--- a/dlfcn/dladdr.c
+++ b/dlfcn/dladdr.c
@@ -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);
diff --git a/dlfcn/dladdr1.c b/dlfcn/dladdr1.c
index a19f9fdea2..901cf43f6b 100644
--- a/dlfcn/dladdr1.c
+++ b/dlfcn/dladdr1.c
@@ -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
diff --git a/dlfcn/dlclose.c b/dlfcn/dlclose.c
index da66e20488..223887d338 100644
--- a/dlfcn/dlclose.c
+++ b/dlfcn/dlclose.c
@@ -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
diff --git a/dlfcn/dlerror.c b/dlfcn/dlerror.c
index fb5012ee85..b33c05095a 100644
--- a/dlfcn/dlerror.c
+++ b/dlfcn/dlerror.c
@@ -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
diff --git a/dlfcn/dlinfo.c b/dlfcn/dlinfo.c
index a34e947ed3..b011257468 100644
--- a/dlfcn/dlinfo.c
+++ b/dlfcn/dlinfo.c
@@ -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
diff --git a/dlfcn/dlmopen.c b/dlfcn/dlmopen.c
index 07d59ade30..58f88bb7c6 100644
--- a/dlfcn/dlmopen.c
+++ b/dlfcn/dlmopen.c
@@ -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
diff --git a/dlfcn/dlopen.c b/dlfcn/dlopen.c
index 22120655d2..73651a8430 100644
--- a/dlfcn/dlopen.c
+++ b/dlfcn/dlopen.c
@@ -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
diff --git a/dlfcn/dlopenold.c b/dlfcn/dlopenold.c
index a3db500705..d899c4e890 100644
--- a/dlfcn/dlopenold.c
+++ b/dlfcn/dlopenold.c
@@ -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;
diff --git a/dlfcn/dlsym.c b/dlfcn/dlsym.c
index 7976c5f75c..19733a0f19 100644
--- a/dlfcn/dlsym.c
+++ b/dlfcn/dlsym.c
@@ -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
diff --git a/dlfcn/dlvsym.c b/dlfcn/dlvsym.c
index 5ed220b77c..ad46b65023 100644
--- a/dlfcn/dlvsym.c
+++ b/dlfcn/dlvsym.c
@@ -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
diff --git a/elf/dl-libc.c b/elf/dl-libc.c
index bd3c18d20f..7d9a8948f3 100644
--- a/elf/dl-libc.c
+++ b/elf/dl-libc.c
@@ -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);
diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
index 196513851f..61313a72ba 100644
--- a/sysdeps/generic/ldsodefs.h
+++ b/sysdeps/generic/ldsodefs.h
@@ -1144,6 +1144,20 @@ 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
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