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.

1 files changed, 74 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index 4bfee94..ce5070f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,79 @@
 2016-06-23  Florian Weimer  <fweimer@redhat.com>
 
+	[BZ #20191]
+	Implement vtable verification in libio.
+	* Makerules (shlib.lds): Place __libc_IO_vtables section.
+	* debug/obprintf_chk.c (_IO_obstack_jumps): Define as vtable.
+	* debug/vdprintf_chk.c (__vdprintf_chk): Call
+	_IO_new_file_init_internal instead of _IO_file_init.
+	* debug/vsnprintf_chk.c (_IO_strn_jumps): Define as vtable.
+	* debug/vsprintf_chk.c (_IO_str_chk_jumps): Likewise.
+	* libio/Makefile (routines): Add vtables.
+	* libio/libioP.h (_IO_JUMPS_FUNC): Call IO_validate_vtable.
+	(_IO_init): Remove, not for internal use.
+	(_IO_init_internal): Declare, internal replacement for _IO_init.
+	(_IO_file_init): Remove, not for internal use.
+	(_IO_new_file_init): Remove, not for internal use.
+	(_IO_new_file_init_internal): Declare, internal replacement for
+	_IO_new_file_init.
+	(_IO_old_file_init): Remove, not for internal use.
+	(_IO_old_file_init_internal): Declare, internal replacement for
+	_IO_old_file_init.
+	(_IO_str_init_static, _IO_str_init_readonly): Remove, not for
+	internal use.
+	(__libc_IO_vtables, IO_accept_foreign_vtables, _IO_vtable_check):
+	Declare.
+	(libio_vtable): New macro.
+	(IO_set_accept_foreign_vtables, _IO_validate_vtable): New inline
+	functions.
+	* libio/fileops.c (_IO_new_file_init_internal): Rename from
+	_IO_new_file_init.
+	(_IO_new_file_init): New externally visible wrapper which disables
+	vtable verification.
+	(_IO_file_jumps, _IO_file_jumps_mmap, _IO_file_jumps_maybe_mmap):
+	Define as vtables.
+	* libio/genops.c (_IO_init_internal): Rename from _IO_init.
+	(_IO_init): New externally visible wrapper which disables
+	vtable verification.
+	* libio/iofdopen.c (_IO_new_fdopen): Call
+	_IO_new_file_init_internal instead of _IO_file_init.  Adjust
+	comment.
+	* libio/iofopen.c (__fopen_internal): Call
+	_IO_new_file_init_internal instead of _IO_file_init.
+	* libio/iofopncook.c (_IO_cookie_jumps, _IO_old_cookie_jumps):
+	Define as vtables.
+	(_IO_cookie_init): Call _IO_init_internal instead of _IO_init,
+	_IO_new_file_init_internal instead of _IO_file_init.
+	* libio/iopopen.c (_IO_new_popen): Likewise.
+	(_IO_proc_jumps): Define as vtable.
+	* libio/iovdprintf.c (_IO_vdprintf): Call
+	_IO_new_file_init_internal instead of _IO_file_init.
+	* libio/memstream.c (_IO_mem_jumps): Define as vtable.
+	(__open_memstream): Call _IO_init_internal instead of _IO_init.
+	* libio/obprintf.c (_IO_obstack_jumps): Define as vtable.
+	* libio/oldfileops.c (_IO_old_file_init_internal): Rename from
+	_IO_old_file_init.
+	(_IO_old_file_init): New externally visible wrapper which disables
+	vtable verification.
+	(_IO_old_file_jumps): Define as vtable.
+	* libio/oldiofdopen.c (_IO_old_fdopen): Call
+	_IO_old_file_init_internal instead of _IO_old_file_init.
+	* libio/oldiofopen.c (_IO_old_fopen): Likewise.
+	* libio/oldiopopen.c (_IO_old_popen): Likewise.
+	(_IO_old_proc_jumps): Define as vtable.
+	* libio/strops.c (_IO_str_jumps, _IO_strn_jumps, _IO_wstrn_jumps):
+	Define as vtables.
+	* libio/vtables.c: New file.
+	* libio/wfileops.c (_IO_wfile_jumps, _IO_wfile_jumps_mmap)
+	(_IO_wfile_jumps_maybe_mmap): Define as vtables.
+	* libio/wmemstream.c (_IO_wmem_jumps): Define as vtable.
+	* libio/wstrops.c (_IO_wstr_jumps): Likewise.
+	* stdio-common/vfprintf.c (_IO_helper_jumps): Likewise.
+	* stdlib/strfmon_l.c (__vstrfmon_l): Call _IO_init_internal
+	instead of _IO_init.
+
+2016-06-23  Florian Weimer  <fweimer@redhat.com>
+
 	* test-skeleton.c (xrealloc): Support deallocation with n == 0.
 
 2016-06-23  Florian Weimer  <fweimer@redhat.com>