commit db3476aff19b75c4fdefbe65fcd5f0a90588ba51
Author: Florian Weimer <fweimer@redhat.com>
Date:   Thu Jun 23 20:01:40 2016 +0200
 
    libio: Implement vtable verification [BZ #20191]
    
    This commit puts all libio vtables in a dedicated, read-only ELF
    section, so that they are consecutive in memory.  Before any indirect
    jump, the vtable pointer is checked against the section boundaries,
    and the process is terminated if the vtable pointer does not fall into
    the special ELF section.
    
    To enable backwards compatibility, a special flag variable
    (_IO_accept_foreign_vtables), protected by the pointer guard, avoids
    process termination if libio stream object constructor functions have
    been called earlier.  Such constructor functions are called by the GCC
    2.95 libstdc++ library, and this mechanism ensures compatibility with
    old binaries.  Existing callers inside glibc of these functions are
    adjusted to call the original functions, not the wrappers which enable
    vtable compatiblity.
    
    The compatibility mechanism is used to enable passing FILE * objects
    across a static dlopen boundary, too.
 
diff -rupN a/Makerules b/Makerules
--- a/Makerules	2017-08-24 14:50:27.000000000 -0400
+++ b/Makerules	2017-08-24 14:56:40.194819878 -0400
@@ -520,6 +520,9 @@ $(common-objpfx)shlib.lds: $(common-objp
 		 PROVIDE(__start___libc_thread_subfreeres = .);\
 		 __libc_thread_subfreeres : { *(__libc_thread_subfreeres) }\
 		 PROVIDE(__stop___libc_thread_subfreeres = .);\
+		 PROVIDE(__start___libc_IO_vtables = .);\
+		 __libc_IO_vtables : { *(__libc_IO_vtables) }\
+		 PROVIDE(__stop___libc_IO_vtables = .);\
 		 /DISCARD/ : { *(.gnu.glibc-stub.*) }@'
 	test -s $@T
 	mv -f $@T $@
diff -rupN a/debug/obprintf_chk.c b/debug/obprintf_chk.c
--- a/debug/obprintf_chk.c	2012-12-24 22:02:13.000000000 -0500
+++ b/debug/obprintf_chk.c	2017-08-24 14:56:40.194819878 -0400
@@ -35,7 +35,7 @@ struct _IO_obstack_file
   struct obstack *obstack;
 };
 
-extern const struct _IO_jump_t _IO_obstack_jumps attribute_hidden;
+extern const struct _IO_jump_t _IO_obstack_jumps libio_vtable attribute_hidden;
 
 int
 __obstack_vprintf_chk (struct obstack *obstack, int flags, const char *format,
diff -rupN a/debug/vdprintf_chk.c b/debug/vdprintf_chk.c
--- a/debug/vdprintf_chk.c	2012-12-24 22:02:13.000000000 -0500
+++ b/debug/vdprintf_chk.c	2017-08-24 14:56:40.194819878 -0400
@@ -39,7 +39,7 @@ __vdprintf_chk (int d, int flags, const
 #endif
   _IO_no_init (&tmpfil.file, _IO_USER_LOCK, 0, &wd, &_IO_wfile_jumps);
   _IO_JUMPS (&tmpfil) = &_IO_file_jumps;
-  _IO_file_init (&tmpfil);
+  _IO_new_file_init_internal (&tmpfil);
 #if  !_IO_UNIFIED_JUMPTABLES
   tmpfil.vtable = NULL;
 #endif
diff -rupN a/debug/vsnprintf_chk.c b/debug/vsnprintf_chk.c
--- a/debug/vsnprintf_chk.c	2012-12-24 22:02:13.000000000 -0500
+++ b/debug/vsnprintf_chk.c	2017-08-24 14:56:40.194819878 -0400
@@ -20,7 +20,7 @@
 #include "../libio/libioP.h"
 #include "../libio/strfile.h"
 
-extern const struct _IO_jump_t _IO_strn_jumps attribute_hidden;
+extern const struct _IO_jump_t _IO_strn_jumps libio_vtable attribute_hidden;
 
 /* Write formatted output into S, according to the format
    string FORMAT, writing no more than MAXLEN characters.  */
diff -rupN a/debug/vsprintf_chk.c b/debug/vsprintf_chk.c
--- a/debug/vsprintf_chk.c	2012-12-24 22:02:13.000000000 -0500
+++ b/debug/vsprintf_chk.c	2017-08-24 14:56:40.194819878 -0400
@@ -34,7 +34,7 @@ _IO_str_chk_overflow (fp, c)
 }
 
 
-static const struct _IO_jump_t _IO_str_chk_jumps =
+static const struct _IO_jump_t _IO_str_chk_jumps libio_vtable =
 {
   JUMP_INIT_DUMMY,
   JUMP_INIT(finish, _IO_str_finish),
diff -rupN a/libio/Makefile b/libio/Makefile
--- a/libio/Makefile	2017-08-24 14:50:22.000000000 -0400
+++ b/libio/Makefile	2017-08-24 17:29:03.754025266 -0400
@@ -44,7 +44,7 @@ routines	:=							      \
 	__fbufsize __freading __fwriting __freadable __fwritable __flbf	      \
 	__fpurge __fpending __fsetlocking				      \
 									      \
-	libc_fatal fmemopen
+	libc_fatal fmemopen vtables
 
 include ../Makeconfig
 
diff -rupN a/libio/fileops.c b/libio/fileops.c
--- a/libio/fileops.c	2017-08-24 14:50:23.000000000 -0400
+++ b/libio/fileops.c	2017-08-24 14:57:57.765902179 -0400
@@ -139,7 +139,7 @@ extern struct __gconv_trans_data __libio
 
 
 void
-_IO_new_file_init (fp)
+_IO_new_file_init_internal (fp)
      struct _IO_FILE_plus *fp;
 {
   /* POSIX.1 allows another file handle to be used to change the position
@@ -151,7 +151,15 @@ _IO_new_file_init (fp)
   _IO_link_in (fp);
   fp->file._fileno = -1;
 }
-libc_hidden_ver (_IO_new_file_init, _IO_file_init)
+
+/* External version of _IO_new_file_init_internal which switches off
+   vtable validation.  */
+void
+_IO_new_file_init (struct _IO_FILE_plus *fp)
+{
+  IO_set_accept_foreign_vtables (&_IO_vtable_check);
+  _IO_new_file_init_internal (fp);
+}
 
 int
 _IO_new_file_close_it (fp)
@@ -1586,7 +1594,7 @@ versioned_symbol (libc, _IO_new_file_wri
 versioned_symbol (libc, _IO_new_file_xsputn, _IO_file_xsputn, GLIBC_2_1);
 #endif
 
-const struct _IO_jump_t _IO_file_jumps =
+const struct _IO_jump_t _IO_file_jumps libio_vtable =
 {
   JUMP_INIT_DUMMY,
   JUMP_INIT(finish, _IO_file_finish),
@@ -1611,7 +1619,7 @@ const struct _IO_jump_t _IO_file_jumps =
 };
 libc_hidden_data_def (_IO_file_jumps)
 
-const struct _IO_jump_t _IO_file_jumps_mmap =
+const struct _IO_jump_t _IO_file_jumps_mmap libio_vtable =
 {
   JUMP_INIT_DUMMY,
   JUMP_INIT(finish, _IO_file_finish),
@@ -1635,7 +1643,7 @@ const struct _IO_jump_t _IO_file_jumps_m
   JUMP_INIT(imbue, _IO_default_imbue)
 };
 
-const struct _IO_jump_t _IO_file_jumps_maybe_mmap =
+const struct _IO_jump_t _IO_file_jumps_maybe_mmap libio_vtable =
 {
   JUMP_INIT_DUMMY,
   JUMP_INIT(finish, _IO_file_finish),
diff -rupN a/libio/genops.c b/libio/genops.c
--- a/libio/genops.c	2012-12-24 22:02:13.000000000 -0500
+++ b/libio/genops.c	2017-08-24 15:44:28.757584527 -0400
@@ -595,13 +595,19 @@ _IO_default_doallocate (fp)
 libc_hidden_def (_IO_default_doallocate)
 
 void
-_IO_init (fp, flags)
+_IO_init_internal (fp, flags)
      _IO_FILE *fp;
      int flags;
 {
   _IO_no_init (fp, flags, -1, NULL, NULL);
 }
-libc_hidden_def (_IO_init)
+
+void
+_IO_init (_IO_FILE *fp, int flags)
+{
+  IO_set_accept_foreign_vtables (&_IO_vtable_check);
+  _IO_init_internal (fp, flags);
+}
 
 void
 _IO_old_init (fp, flags)
diff -rupN a/libio/iofdopen.c b/libio/iofdopen.c
--- a/libio/iofdopen.c	2017-08-24 14:50:21.000000000 -0400
+++ b/libio/iofdopen.c	2017-08-24 14:56:40.220819906 -0400
@@ -158,15 +158,15 @@ _IO_new_fdopen (fd, mode)
     (use_mmap && (read_write & _IO_NO_WRITES)) ? &_IO_file_jumps_maybe_mmap :
 #endif
       &_IO_file_jumps;
-  _IO_file_init (&new_f->fp);
+  _IO_new_file_init_internal (&new_f->fp);
 #if  !_IO_UNIFIED_JUMPTABLES
   new_f->fp.vtable = NULL;
 #endif
-  /* We only need to record the fd because _IO_file_init will have unset the
-     offset.  It is important to unset the cached offset because the real
-     offset in the file could change between now and when the handle is
-     activated and we would then mislead ftell into believing that we have a
-     valid offset.  */
+  /* We only need to record the fd because _IO_file_init_internal will
+     have unset the offset.  It is important to unset the cached
+     offset because the real offset in the file could change between
+     now and when the handle is activated and we would then mislead
+     ftell into believing that we have a valid offset.  */
   new_f->fp.file._fileno = fd;
   new_f->fp.file._flags &= ~_IO_DELETE_DONT_CLOSE;
 
diff -rupN a/libio/iofopen.c b/libio/iofopen.c
--- a/libio/iofopen.c	2012-12-24 22:02:13.000000000 -0500
+++ b/libio/iofopen.c	2017-08-24 14:56:40.223819909 -0400
@@ -83,7 +83,7 @@ __fopen_internal (filename, mode, is32)
   _IO_no_init (&new_f->fp.file, 1, 0, NULL, NULL);
 #endif
   _IO_JUMPS (&new_f->fp) = &_IO_file_jumps;
-  _IO_file_init (&new_f->fp);
+  _IO_new_file_init_internal (&new_f->fp);
 #if  !_IO_UNIFIED_JUMPTABLES
   new_f->fp.vtable = NULL;
 #endif
diff -rupN a/libio/iofopncook.c b/libio/iofopncook.c
--- a/libio/iofopncook.c	2012-12-24 22:02:13.000000000 -0500
+++ b/libio/iofopncook.c	2017-08-24 15:46:49.061694225 -0400
@@ -116,7 +116,7 @@ _IO_cookie_seekoff (fp, offset, dir, mod
 }
 
 
-static const struct _IO_jump_t _IO_cookie_jumps = {
+static const struct _IO_jump_t _IO_cookie_jumps libio_vtable = {
   JUMP_INIT_DUMMY,
   JUMP_INIT(finish, _IO_file_finish),
   JUMP_INIT(overflow, _IO_file_overflow),
@@ -144,13 +144,13 @@ void
 _IO_cookie_init (struct _IO_cookie_file *cfile, int read_write,
 		 void *cookie, _IO_cookie_io_functions_t io_functions)
 {
-  _IO_init (&cfile->__fp.file, 0);
+  _IO_init_internal (&cfile->__fp.file, 0);
   _IO_JUMPS (&cfile->__fp) = &_IO_cookie_jumps;
 
   cfile->__cookie = cookie;
   cfile->__io_functions = io_functions;
 
-  _IO_file_init (&cfile->__fp);
+  _IO_new_file_init_internal (&cfile->__fp);
 
   _IO_mask_flags (&cfile->__fp.file, read_write,
 		  _IO_NO_READS+_IO_NO_WRITES+_IO_IS_APPENDING);
@@ -235,7 +235,7 @@ _IO_old_cookie_seek (fp, offset, dir)
   return (ret == -1) ? _IO_pos_BAD : ret;
 }
 
-static const struct _IO_jump_t _IO_old_cookie_jumps = {
+static const struct _IO_jump_t _IO_old_cookie_jumps libio_vtable = {
   JUMP_INIT_DUMMY,
   JUMP_INIT(finish, _IO_file_finish),
   JUMP_INIT(overflow, _IO_file_overflow),
diff -rupN a/libio/iopopen.c b/libio/iopopen.c
--- a/libio/iopopen.c	2012-12-24 22:02:13.000000000 -0500
+++ b/libio/iopopen.c	2017-08-24 14:56:40.234819921 -0400
@@ -292,9 +292,9 @@ _IO_new_popen (command, mode)
   new_f->fpx.file.file._lock = &new_f->lock;
 #endif
   fp = &new_f->fpx.file.file;
-  _IO_init (fp, 0);
+  _IO_init_internal (fp, 0);
   _IO_JUMPS (&new_f->fpx.file) = &_IO_proc_jumps;
-  _IO_new_file_init (&new_f->fpx.file);
+  _IO_new_file_init_internal (&new_f->fpx.file);
 #if  !_IO_UNIFIED_JUMPTABLES
   new_f->fpx.file.vtable = NULL;
 #endif
@@ -350,7 +350,7 @@ _IO_new_proc_close (fp)
   return wstatus;
 }
 
-static const struct _IO_jump_t _IO_proc_jumps = {
+static const struct _IO_jump_t _IO_proc_jumps libio_vtable = {
   JUMP_INIT_DUMMY,
   JUMP_INIT(finish, _IO_new_file_finish),
   JUMP_INIT(overflow, _IO_new_file_overflow),
diff -rupN a/libio/iovdprintf.c b/libio/iovdprintf.c
--- a/libio/iovdprintf.c	2012-12-24 22:02:13.000000000 -0500
+++ b/libio/iovdprintf.c	2017-08-24 14:56:40.237819924 -0400
@@ -42,7 +42,7 @@ _IO_vdprintf (d, format, arg)
 #endif
   _IO_no_init (&tmpfil.file, _IO_USER_LOCK, 0, &wd, &_IO_wfile_jumps);
   _IO_JUMPS (&tmpfil) = &_IO_file_jumps;
-  _IO_file_init (&tmpfil);
+  _IO_new_file_init_internal (&tmpfil);
 #if  !_IO_UNIFIED_JUMPTABLES
   tmpfil.vtable = NULL;
 #endif
diff -rupN a/libio/libioP.h b/libio/libioP.h
--- a/libio/libioP.h	2017-08-24 14:50:26.000000000 -0400
+++ b/libio/libioP.h	2017-08-24 17:26:39.918165252 -0400
@@ -108,11 +108,12 @@ extern "C" {
 
 #if _IO_JUMPS_OFFSET
 # define _IO_JUMPS_FUNC(THIS) \
- (*(struct _IO_jump_t **) ((void *) &_IO_JUMPS ((struct _IO_FILE_plus *) (THIS)) \
-			   + (THIS)->_vtable_offset))
+  (IO_validate_vtable                                                   \
+   (*(struct _IO_jump_t **) ((void *) &_IO_JUMPS ((struct _IO_FILE_plus *) (THIS)) \
+			     + (THIS)->_vtable_offset)))
 # define _IO_vtable_offset(THIS) (THIS)->_vtable_offset
 #else
-# define _IO_JUMPS_FUNC(THIS) _IO_JUMPS ((struct _IO_FILE_plus *) (THIS))
+# define _IO_JUMPS_FUNC(THIS) (IO_validate_vtable (_IO_JUMPS ((struct _IO_FILE_plus *) (THIS))))
 # define _IO_vtable_offset(THIS) 0
 #endif
 #define _IO_WIDE_JUMPS_FUNC(THIS) _IO_WIDE_JUMPS(THIS)
@@ -361,8 +362,7 @@ extern void _IO_switch_to_main_get_area
 extern void _IO_switch_to_backup_area (_IO_FILE *) __THROW;
 extern int _IO_switch_to_get_mode (_IO_FILE *);
 libc_hidden_proto (_IO_switch_to_get_mode)
-extern void _IO_init (_IO_FILE *, int) __THROW;
-libc_hidden_proto (_IO_init)
+extern void _IO_init_internal (_IO_FILE *, int) attribute_hidden;
 extern int _IO_sputbackc (_IO_FILE *, int) __THROW;
 libc_hidden_proto (_IO_sputbackc)
 extern int _IO_sungetc (_IO_FILE *) __THROW;
@@ -570,8 +570,6 @@ extern int _IO_file_underflow_maybe_mmap
 extern int _IO_file_overflow (_IO_FILE *, int);
 libc_hidden_proto (_IO_file_overflow)
 #define _IO_file_is_open(__fp) ((__fp)->_fileno != -1)
-extern void _IO_file_init (struct _IO_FILE_plus *) __THROW;
-libc_hidden_proto (_IO_file_init)
 extern _IO_FILE* _IO_file_attach (_IO_FILE *, int);
 libc_hidden_proto (_IO_file_attach)
 extern _IO_FILE* _IO_file_open (_IO_FILE *, const char *, int, int, int, int);
@@ -597,7 +595,8 @@ extern _IO_FILE* _IO_new_file_fopen (_IO
 				     int);
 extern void _IO_no_init (_IO_FILE *, int, int, struct _IO_wide_data *,
 			 const struct _IO_jump_t *) __THROW;
-extern void _IO_new_file_init (struct _IO_FILE_plus *) __THROW;
+extern void _IO_new_file_init_internal (struct _IO_FILE_plus *)
+  __THROW attribute_hidden;
 extern _IO_FILE* _IO_new_file_setbuf (_IO_FILE *, char *, _IO_ssize_t);
 extern _IO_FILE* _IO_file_setbuf_mmap (_IO_FILE *, char *, _IO_ssize_t);
 extern int _IO_new_file_sync (_IO_FILE *);
@@ -612,7 +611,8 @@ extern _IO_off64_t _IO_old_file_seekoff
 extern _IO_size_t _IO_old_file_xsputn (_IO_FILE *, const void *, _IO_size_t);
 extern int _IO_old_file_underflow (_IO_FILE *);
 extern int _IO_old_file_overflow (_IO_FILE *, int);
-extern void _IO_old_file_init (struct _IO_FILE_plus *) __THROW;
+extern void _IO_old_file_init_internal (struct _IO_FILE_plus *)
+  __THROW attribute_hidden;
 extern _IO_FILE* _IO_old_file_attach (_IO_FILE *, int);
 extern _IO_FILE* _IO_old_file_fopen (_IO_FILE *, const char *, const char *);
 extern _IO_ssize_t _IO_old_file_write (_IO_FILE *, const void *, _IO_ssize_t);
@@ -656,10 +656,6 @@ extern void _IO_str_finish (_IO_FILE *,
 
 /* Other strfile functions */
 struct _IO_strfile_;
-extern void _IO_str_init_static (struct _IO_strfile_ *, char *, int, char *)
-     __THROW;
-extern void _IO_str_init_readonly (struct _IO_strfile_ *, const char *, int)
-     __THROW;
 extern _IO_ssize_t _IO_str_count (_IO_FILE *) __THROW;
 
 /* And the wide character versions.  */
@@ -913,3 +909,57 @@ _IO_acquire_lock_clear_flags2_fct (_IO_F
                                           | _IO_FLAGS2_SCANF_STD);	      \
   } while (0)
 #endif
+
+/* Collect all vtables in a special section for vtable verification.
+   These symbols cover the extent of this section.  */
+symbol_set_declare (__libc_IO_vtables)
+
+/* libio vtables need to carry this attribute so that they pass
+   validation.  */
+#define libio_vtable __attribute__ ((section ("__libc_IO_vtables")))
+
+#ifdef SHARED
+/* If equal to &_IO_vtable_check (with pointer guard protection),
+   unknown vtable pointers are valid.  This function pointer is solely
+   used as a flag.  */
+extern void (*IO_accept_foreign_vtables) (void) attribute_hidden;
+
+/* Assigns the passed function pointer (either NULL or
+   &_IO_vtable_check) to IO_accept_foreign_vtables.  */
+static inline void
+IO_set_accept_foreign_vtables (void (*flag) (void))
+{
+  PTR_MANGLE (flag);
+  atomic_store_relaxed (&IO_accept_foreign_vtables, flag);
+}
+
+#else  /* !SHARED */
+
+/* The statically-linked version does nothing. */
+static inline void
+IO_set_accept_foreign_vtables (void (*flag) (void))
+{
+}
+
+#endif
+
+/* Check if unknown vtable pointers are permitted; otherwise,
+   terminate the process.  */
+void _IO_vtable_check (void) attribute_hidden;
+
+/* Perform vtable pointer validation.  If validation fails, terminate
+   the process.  */
+static inline const struct _IO_jump_t *
+IO_validate_vtable (const struct _IO_jump_t *vtable)
+{
+  /* Fast path: The vtable pointer is within the __libc_IO_vtables
+     section.  */
+  uintptr_t section_length = __stop___libc_IO_vtables - __start___libc_IO_vtables;
+  const char *ptr = (const char *) vtable;
+  uintptr_t offset = ptr - __start___libc_IO_vtables;
+  if (__glibc_unlikely (offset >= section_length))
+    /* The vtable pointer is not in the expected section.  Use the
+       slow path, which will terminate the process if necessary.  */
+    _IO_vtable_check ();
+  return vtable;
+}
diff -rupN a/libio/memstream.c b/libio/memstream.c
--- a/libio/memstream.c	2012-12-24 22:02:13.000000000 -0500
+++ b/libio/memstream.c	2017-08-24 15:56:02.643120827 -0400
@@ -33,7 +33,7 @@ static int _IO_mem_sync (_IO_FILE* fp) _
 static void _IO_mem_finish (_IO_FILE* fp, int) __THROW;
 
 
-static const struct _IO_jump_t _IO_mem_jumps =
+static const struct _IO_jump_t _IO_mem_jumps libio_vtable =
 {
   JUMP_INIT_DUMMY,
   JUMP_INIT (finish, _IO_mem_finish),
@@ -85,7 +85,7 @@ open_memstream (bufloc, sizeloc)
   buf = calloc (1, _IO_BUFSIZ);
   if (buf == NULL)
     return NULL;
-  _IO_init (&new_f->fp._sf._sbf._f, 0);
+  _IO_init_internal (&new_f->fp._sf._sbf._f, 0);
   _IO_JUMPS ((struct _IO_FILE_plus *) &new_f->fp._sf._sbf) = &_IO_mem_jumps;
   _IO_str_init_static_internal (&new_f->fp._sf, buf, _IO_BUFSIZ, buf);
   new_f->fp._sf._sbf._f._flags &= ~_IO_USER_BUF;
diff -rupN a/libio/obprintf.c b/libio/obprintf.c
--- a/libio/obprintf.c	2012-12-24 22:02:13.000000000 -0500
+++ b/libio/obprintf.c	2017-08-24 14:56:40.255819944 -0400
@@ -91,7 +91,7 @@ _IO_obstack_xsputn (_IO_FILE *fp, const
 
 
 /* the jump table.  */
-const struct _IO_jump_t _IO_obstack_jumps attribute_hidden =
+const struct _IO_jump_t _IO_obstack_jumps libio_vtable attribute_hidden =
 {
   JUMP_INIT_DUMMY,
   JUMP_INIT(finish, NULL),
diff -rupN a/libio/oldfileops.c b/libio/oldfileops.c
--- a/libio/oldfileops.c	2012-12-24 22:02:13.000000000 -0500
+++ b/libio/oldfileops.c	2017-08-24 15:56:27.333139635 -0400
@@ -113,7 +113,7 @@ extern int errno;
 
 void
 attribute_compat_text_section
-_IO_old_file_init (fp)
+_IO_old_file_init_internal (fp)
      struct _IO_FILE_plus *fp;
 {
   /* POSIX.1 allows another file handle to be used to change the position
@@ -138,6 +138,14 @@ _IO_old_file_init (fp)
 #endif
 }
 
+void
+attribute_compat_text_section
+_IO_old_file_init (struct _IO_FILE_plus *fp)
+{
+  IO_set_accept_foreign_vtables (&_IO_vtable_check);
+  _IO_old_file_init_internal (fp);
+}
+
 int
 attribute_compat_text_section
 _IO_old_file_close_it (fp)
@@ -776,7 +784,7 @@ _IO_old_file_xsputn (f, data, n)
 }
 
 
-const struct _IO_jump_t _IO_old_file_jumps =
+const struct _IO_jump_t _IO_old_file_jumps libio_vtable =
 {
   JUMP_INIT_DUMMY,
   JUMP_INIT(finish, _IO_old_file_finish),
diff -rupN a/libio/oldiofdopen.c b/libio/oldiofdopen.c
--- a/libio/oldiofdopen.c	2012-12-24 22:02:13.000000000 -0500
+++ b/libio/oldiofdopen.c	2017-08-24 15:57:15.823176524 -0400
@@ -114,7 +114,7 @@ _IO_old_fdopen (fd, mode)
 #endif
   _IO_old_init (&new_f->fp.file._file, 0);
   _IO_JUMPS ((struct _IO_FILE_plus *) &new_f->fp) = &_IO_old_file_jumps;
-  _IO_old_file_init ((struct _IO_FILE_plus *) &new_f->fp);
+  _IO_old_file_init_internal ((struct _IO_FILE_plus *) &new_f->fp);
 #if  !_IO_UNIFIED_JUMPTABLES
   new_f->fp.vtable = NULL;
 #endif
diff -rupN a/libio/oldiofopen.c b/libio/oldiofopen.c
--- a/libio/oldiofopen.c	2012-12-24 22:02:13.000000000 -0500
+++ b/libio/oldiofopen.c	2017-08-24 15:58:13.978220676 -0400
@@ -53,7 +53,7 @@ _IO_old_fopen (filename, mode)
 #endif
   _IO_old_init (&new_f->fp.file._file, 0);
   _IO_JUMPS ((struct _IO_FILE_plus *) &new_f->fp) = &_IO_old_file_jumps;
-  _IO_old_file_init ((struct _IO_FILE_plus *) &new_f->fp);
+  _IO_old_file_init_internal ((struct _IO_FILE_plus *) &new_f->fp);
 #if  !_IO_UNIFIED_JUMPTABLES
   new_f->fp.vtable = NULL;
 #endif
diff -rupN a/libio/oldiopopen.c b/libio/oldiopopen.c
--- a/libio/oldiopopen.c	2012-12-24 22:02:13.000000000 -0500
+++ b/libio/oldiopopen.c	2017-08-24 15:58:32.060234383 -0400
@@ -216,7 +216,7 @@ _IO_old_popen (command, mode)
   fp = &new_f->fpx.file.file._file;
   _IO_old_init (fp, 0);
   _IO_JUMPS ((struct _IO_FILE_plus *) &new_f->fpx.file) = &_IO_old_proc_jumps;
-  _IO_old_file_init ((struct _IO_FILE_plus *) &new_f->fpx.file);
+  _IO_old_file_init_internal ((struct _IO_FILE_plus *) &new_f->fpx.file);
 #if  !_IO_UNIFIED_JUMPTABLES
   new_f->fpx.file.vtable = NULL;
 #endif
@@ -273,7 +273,7 @@ _IO_old_proc_close (fp)
   return wstatus;
 }
 
-const struct _IO_jump_t _IO_old_proc_jumps = {
+const struct _IO_jump_t _IO_old_proc_jumps libio_vtable = {
   JUMP_INIT_DUMMY,
   JUMP_INIT(finish, _IO_old_file_finish),
   JUMP_INIT(overflow, _IO_old_file_overflow),
diff -rupN a/libio/strops.c b/libio/strops.c
--- a/libio/strops.c	2012-12-24 22:02:13.000000000 -0500
+++ b/libio/strops.c	2017-08-24 14:56:40.289819980 -0400
@@ -345,7 +345,7 @@ _IO_str_finish (fp, dummy)
   _IO_default_finish (fp, 0);
 }
 
-const struct _IO_jump_t _IO_str_jumps =
+const struct _IO_jump_t _IO_str_jumps libio_vtable =
 {
   JUMP_INIT_DUMMY,
   JUMP_INIT(finish, _IO_str_finish),
diff -rupN a/libio/vsnprintf.c b/libio/vsnprintf.c
--- a/libio/vsnprintf.c	2012-12-24 22:02:13.000000000 -0500
+++ b/libio/vsnprintf.c	2017-08-24 14:56:40.292819983 -0400
@@ -66,7 +66,7 @@ _IO_strn_overflow (fp, c)
 }
 
 
-const struct _IO_jump_t _IO_strn_jumps attribute_hidden =
+const struct _IO_jump_t _IO_strn_jumps libio_vtable attribute_hidden =
 {
   JUMP_INIT_DUMMY,
   JUMP_INIT(finish, _IO_str_finish),
diff -rupN a/libio/vswprintf.c b/libio/vswprintf.c
--- a/libio/vswprintf.c	2012-12-24 22:02:13.000000000 -0500
+++ b/libio/vswprintf.c	2017-08-24 14:56:40.296819988 -0400
@@ -65,7 +65,7 @@ _IO_wstrn_overflow (fp, c)
 }
 
 
-const struct _IO_jump_t _IO_wstrn_jumps attribute_hidden =
+const struct _IO_jump_t _IO_wstrn_jumps libio_vtable attribute_hidden =
 {
   JUMP_INIT_DUMMY,
   JUMP_INIT(finish, _IO_wstr_finish),
diff -rupN a/libio/vtables.c b/libio/vtables.c
--- a/libio/vtables.c	1969-12-31 19:00:00.000000000 -0500
+++ b/libio/vtables.c	2017-08-24 14:56:40.299819991 -0400
@@ -0,0 +1,70 @@
+/* libio vtable validation.
+   Copyright (C) 2016 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <dlfcn.h>
+#include <libioP.h>
+#include <stdio.h>
+
+#ifdef SHARED
+
+void (*IO_accept_foreign_vtables) (void) attribute_hidden;
+
+/* Used to detected multiple libcs.  */
+extern struct dl_open_hook *_dl_open_hook;
+libc_hidden_proto (_dl_open_hook);
+
+#else  /* !SHARED */
+
+/* Used to check whether static dlopen support is needed.  */
+# pragma weak __dlopen
+
+#endif
+
+void attribute_hidden
+_IO_vtable_check (void)
+{
+#ifdef SHARED
+  /* Honor the compatibility flag.  */
+  void (*flag) (void) = atomic_load_relaxed (&IO_accept_foreign_vtables);
+  PTR_DEMANGLE (flag);
+  if (flag == &_IO_vtable_check)
+    return;
+
+  /* In case this libc copy is in a non-default namespace, we always
+     need to accept foreign vtables because there is always a
+     possibility that FILE * objects are passed across the linking
+     boundary.  */
+  {
+    Dl_info di;
+    struct link_map *l;
+    if (_dl_open_hook != NULL
+        || (_dl_addr (_IO_vtable_check, &di, &l, NULL) != 0
+            && l->l_ns != LM_ID_BASE))
+      return;
+  }
+
+#else /* !SHARED */
+  /* We cannot perform vtable validation in the static dlopen case
+     because FILE * handles might be passed back and forth across the
+     boundary.  Therefore, we disable checking in this case.  */
+  if (__dlopen != NULL)
+    return;
+#endif
+
+  __libc_fatal ("Fatal error: glibc detected an invalid stdio handle\n");
+}
diff -rupN a/libio/wfileops.c b/libio/wfileops.c
--- a/libio/wfileops.c	2017-08-24 14:50:25.000000000 -0400
+++ b/libio/wfileops.c	2017-08-24 14:56:40.303819995 -0400
@@ -1035,7 +1035,7 @@ _IO_wfile_xsputn (f, data, n)
 libc_hidden_def (_IO_wfile_xsputn)
 
 
-const struct _IO_jump_t _IO_wfile_jumps =
+const struct _IO_jump_t _IO_wfile_jumps libio_vtable =
 {
   JUMP_INIT_DUMMY,
   JUMP_INIT(finish, _IO_new_file_finish),
@@ -1061,7 +1061,7 @@ const struct _IO_jump_t _IO_wfile_jumps
 libc_hidden_data_def (_IO_wfile_jumps)
 
 
-const struct _IO_jump_t _IO_wfile_jumps_mmap =
+const struct _IO_jump_t _IO_wfile_jumps_mmap libio_vtable =
 {
   JUMP_INIT_DUMMY,
   JUMP_INIT(finish, _IO_new_file_finish),
@@ -1085,7 +1085,7 @@ const struct _IO_jump_t _IO_wfile_jumps_
   JUMP_INIT(imbue, _IO_default_imbue)
 };
 
-const struct _IO_jump_t _IO_wfile_jumps_maybe_mmap =
+const struct _IO_jump_t _IO_wfile_jumps_maybe_mmap libio_vtable =
 {
   JUMP_INIT_DUMMY,
   JUMP_INIT(finish, _IO_new_file_finish),
diff -rupN a/libio/wmemstream.c b/libio/wmemstream.c
--- a/libio/wmemstream.c	2012-12-24 22:02:13.000000000 -0500
+++ b/libio/wmemstream.c	2017-08-24 14:56:40.307819999 -0400
@@ -34,7 +34,7 @@ static int _IO_wmem_sync (_IO_FILE* fp)
 static void _IO_wmem_finish (_IO_FILE* fp, int) __THROW;
 
 
-static const struct _IO_jump_t _IO_wmem_jumps =
+static const struct _IO_jump_t _IO_wmem_jumps libio_vtable =
 {
   JUMP_INIT_DUMMY,
   JUMP_INIT (finish, _IO_wmem_finish),
diff -rupN a/libio/wstrops.c b/libio/wstrops.c
--- a/libio/wstrops.c	2017-08-24 14:50:23.000000000 -0400
+++ b/libio/wstrops.c	2017-08-24 14:56:40.310820002 -0400
@@ -347,7 +347,7 @@ _IO_wstr_finish (fp, dummy)
   _IO_wdefault_finish (fp, 0);
 }
 
-const struct _IO_jump_t _IO_wstr_jumps =
+const struct _IO_jump_t _IO_wstr_jumps libio_vtable =
 {
   JUMP_INIT_DUMMY,
   JUMP_INIT(finish, _IO_wstr_finish),
diff -rupN a/stdio-common/vfprintf.c b/stdio-common/vfprintf.c
--- a/stdio-common/vfprintf.c	2017-08-24 14:50:20.000000000 -0400
+++ b/stdio-common/vfprintf.c	2017-08-24 14:56:40.314820007 -0400
@@ -2234,7 +2234,7 @@ _IO_helper_overflow (_IO_FILE *s, int c)
 }
 
 #ifdef COMPILE_WPRINTF
-static const struct _IO_jump_t _IO_helper_jumps =
+static const struct _IO_jump_t _IO_helper_jumps libio_vtable =
 {
   JUMP_INIT_DUMMY,
   JUMP_INIT (finish, _IO_wdefault_finish),
@@ -2256,7 +2256,7 @@ static const struct _IO_jump_t _IO_helpe
   JUMP_INIT (stat, _IO_default_stat)
 };
 #else
-static const struct _IO_jump_t _IO_helper_jumps =
+static const struct _IO_jump_t _IO_helper_jumps libio_vtable =
 {
   JUMP_INIT_DUMMY,
   JUMP_INIT (finish, _IO_default_finish),
diff -rupN a/stdlib/strfmon_l.c b/stdlib/strfmon_l.c
--- a/stdlib/strfmon_l.c	2012-12-24 22:02:13.000000000 -0500
+++ b/stdlib/strfmon_l.c	2017-08-24 14:56:40.314820007 -0400
@@ -515,7 +515,7 @@ __vstrfmon_l (char *s, size_t maxsize, _
 #ifdef _IO_MTSAFE_IO
       f._sbf._f._lock = NULL;
 #endif
-      _IO_init (&f._sbf._f, 0);
+      _IO_init_internal (&f._sbf._f, 0);
       _IO_JUMPS (&f._sbf) = &_IO_str_jumps;
       _IO_str_init_static_internal (&f, dest, (s + maxsize) - dest, dest);
       /* We clear the last available byte so we can find out whether