Re: [PATCH] Avoid backtrace from __stack_chk_fail [BZ #12189]

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Tue, Jul 11, 2017 at 10:49:04AM +0200, Florian Weimer wrote:
> * H. J. Lu:
> 
> > __stack_chk_fail is called on corrupted stack.  __stack_chk_fail should
> > use as little stack as possible.  __libc_message is extended to avoid
> > calling BEFORE_ABORT when do_abort >= 3 and __fortify_fail_abort is
> > added to avoid backtrace from __stack_chk_fail.
> >
> > OK for master?
> 
> I think you should use an enum for do_abort and avoid the magic
> numbers.

Done.

> 
> Could you post an example of the new output?

[hjl@gnu-tools-1 debug]$ ./tst-ssp-1
*** stack smashing detected ***: ./tst-ssp-1 terminated
(gdb) r --direct
Starting program: /export/build/gnu/glibc/build-x86_64-linux/debug/tst-ssp-1 --direct
*** stack smashing detected ***: /export/build/gnu/glibc/build-x86_64-linux/debug/tst-ssp-1 terminated

Program received signal SIGABRT, Aborted.
__GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51
51	}
(gdb) bt
#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51
#1  0x00007ffff7a5e4e5 in __GI_abort () at abort.c:90
#2  0x00007ffff7a9db98 in __libc_message (action=action@entry=do_abort, 
    fmt=fmt@entry=0x7ffff7b9d0c2 "*** %s ***: %s terminated\n")
    at ../sysdeps/posix/libc_fatal.c:176
#3  0x00007ffff7b29a57 in __GI___fortify_fail_abort (
    do_backtrace=do_backtrace@entry=false, 
    msg=msg@entry=0x7ffff7b9d0aa "stack smashing detected")
    at fortify_fail.c:31
#4  0x00007ffff7b29a12 in __stack_chk_fail () at stack_chk_fail.c:29
#5  0x000000000040138b in do_test () at tst-ssp-1.c:42
#6  0x2a2a2a2a2a2a2a2a in ?? () <<<< Stack is corrupted
#7  0x2a2a2a2a2a2a2a2a in ?? ()
#8  0x2a2a2a2a2a2a2a2a in ?? ()
#9  0x2a2a2a2a2a2a2a2a in ?? ()


Here is the updated patch.  OK for master?


H.J.
---
__stack_chk_fail is called on corrupted stack. Stack backtrace is very
unreliable against corrupted stack.  __libc_message is changed to accept
enum __libc_message_action and call BEFORE_ABORT only if action includes
do_backtrace.  __fortify_fail_abort is added to avoid backtrace from
__stack_chk_fail.

	[BZ #12189]
	* debug/Makefile (CFLAGS-tst-ssp-1.c): New.
	(tests): Add tst-ssp-1 if -fstack-protector works.
	* debug/fortify_fail.c: Include <stdbool.h>.
	(_fortify_fail_abort): New function.
	(__fortify_fail): Call _fortify_fail_abort.
	(__fortify_fail_abort): Add a hidden definition.
	* debug/stack_chk_fail.c: Include <stdbool.h>.
	(__stack_chk_fail): Call __fortify_fail_abort, instead of
	__fortify_fail.
	* debug/tst-ssp-1.c: New file.
	* include/stdio.h (__libc_message_action): New enum.
	(__libc_message): Replace int with enum __libc_message_action.
	(__fortify_fail_abort): New hidden prototype.
	* malloc/malloc.c (malloc_printerr): Update __libc_message calls.
	* sysdeps/posix/libc_fatal.c (__libc_message): Replace int
	with enum __libc_message_action.  Call BEFORE_ABORT only if
	action includes do_backtrace.
	(__libc_fatal): Update __libc_message call.
---
 debug/Makefile             |  6 ++++++
 debug/fortify_fail.c       | 15 +++++++++++++--
 debug/stack_chk_fail.c     |  3 ++-
 debug/tst-ssp-1.c          | 45 +++++++++++++++++++++++++++++++++++++++++++++
 include/stdio.h            | 13 ++++++++++++-
 malloc/malloc.c            |  6 ++++--
 sysdeps/posix/libc_fatal.c | 11 ++++++-----
 7 files changed, 88 insertions(+), 11 deletions(-)
 create mode 100644 debug/tst-ssp-1.c

diff --git a/debug/Makefile b/debug/Makefile
index cd4975c..c6d7872 100644
--- a/debug/Makefile
+++ b/debug/Makefile
@@ -139,12 +139,18 @@ LDFLAGS-tst-backtrace4 = -rdynamic
 LDFLAGS-tst-backtrace5 = -rdynamic
 LDFLAGS-tst-backtrace6 = -rdynamic
 
+CFLAGS-tst-ssp-1.c = -fstack-protector
+
 tests = backtrace-tst tst-longjmp_chk tst-chk1 tst-chk2 tst-chk3 \
 	tst-lfschk1 tst-lfschk2 tst-lfschk3 test-strcpy_chk test-stpcpy_chk \
 	tst-chk4 tst-chk5 tst-chk6 tst-lfschk4 tst-lfschk5 tst-lfschk6 \
 	tst-longjmp_chk2 tst-backtrace2 tst-backtrace3 tst-backtrace4 \
 	tst-backtrace5 tst-backtrace6
 
+ifeq ($(have-ssp),yes)
+tests += tst-ssp-1
+endif
+
 ifeq (,$(CXX))
 tests-unsupported = tst-chk4 tst-chk5 tst-chk6 \
 		    tst-lfschk4 tst-lfschk5 tst-lfschk6
diff --git a/debug/fortify_fail.c b/debug/fortify_fail.c
index a31977a..c90d384 100644
--- a/debug/fortify_fail.c
+++ b/debug/fortify_fail.c
@@ -17,17 +17,28 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <stdbool.h>
 
 
 extern char **__libc_argv attribute_hidden;
 
 void
 __attribute__ ((noreturn)) internal_function
-__fortify_fail (const char *msg)
+__fortify_fail_abort (_Bool do_backtrace, const char *msg)
 {
   /* The loop is added only to keep gcc happy.  */
   while (1)
-    __libc_message (2, "*** %s ***: %s terminated\n",
+    __libc_message (do_backtrace ? (do_abort | do_backtrace) : do_abort,
+		    "*** %s ***: %s terminated\n",
 		    msg, __libc_argv[0] ?: "<unknown>");
 }
+
+void
+__attribute__ ((noreturn)) internal_function
+__fortify_fail (const char *msg)
+{
+  __fortify_fail_abort (true, msg);
+}
+
 libc_hidden_def (__fortify_fail)
+libc_hidden_def (__fortify_fail_abort)
diff --git a/debug/stack_chk_fail.c b/debug/stack_chk_fail.c
index 120d269..4b099b5 100644
--- a/debug/stack_chk_fail.c
+++ b/debug/stack_chk_fail.c
@@ -17,6 +17,7 @@
 
 #include <stdio.h>
 #include <stdlib.h>
+#include <stdbool.h>
 
 
 extern char **__libc_argv attribute_hidden;
@@ -25,7 +26,7 @@ void
 __attribute__ ((noreturn))
 __stack_chk_fail (void)
 {
-  __fortify_fail ("stack smashing detected");
+  __fortify_fail_abort (false, "stack smashing detected");
 }
 
 #ifdef SHARED
diff --git a/debug/tst-ssp-1.c b/debug/tst-ssp-1.c
new file mode 100644
index 0000000..52c67e2
--- /dev/null
+++ b/debug/tst-ssp-1.c
@@ -0,0 +1,45 @@
+/* Verify that __stack_chk_fail won't segfault.
+   Copyright (C) 2017 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/>.  */
+
+/* Based on gcc.dg/ssp-1.c from GCC testsuite.  */
+
+#include <signal.h>
+
+static void
+__attribute__ ((noinline, noclone))
+test (char *foo)
+{
+  int i;
+
+  /* smash stack */
+  for (i = 0; i <= 400; i++)
+    foo[i] = 42;
+}
+
+static int
+do_test (void)
+{
+  char foo[30];
+
+  test (foo);
+
+  return 1; /* fail */
+}
+
+#define EXPECTED_SIGNAL SIGABRT
+#include <support/test-driver.c>
diff --git a/include/stdio.h b/include/stdio.h
index f68f633..215f919 100644
--- a/include/stdio.h
+++ b/include/stdio.h
@@ -86,13 +86,24 @@ extern int __gen_tempname (char *__tmpl, int __suffixlen, int __flags,
 #  define __GT_DIR	1	/* create a directory */
 #  define __GT_NOCREATE	2	/* just find a name not currently in use */
 
+enum __libc_message_action
+{
+  do_message	= 0,		/* Print message.  */
+  do_abort	= 1 << 0,	/* Abort.  */
+  do_backtrace	= 1 << 1	/* Backtrace.  */
+};
+
 /* Print out MESSAGE on the error output and abort.  */
 extern void __libc_fatal (const char *__message)
      __attribute__ ((__noreturn__));
-extern void __libc_message (int do_abort, const char *__fnt, ...);
+extern void __libc_message (enum __libc_message_action action,
+			    const char *__fnt, ...);
 extern void __fortify_fail (const char *msg)
      __attribute__ ((__noreturn__)) internal_function;
+extern void __fortify_fail_abort (_Bool, const char *msg)
+     __attribute__ ((__noreturn__)) internal_function;
 libc_hidden_proto (__fortify_fail)
+libc_hidden_proto (__fortify_fail_abort)
 
 /* Acquire ownership of STREAM.  */
 extern void __flockfile (FILE *__stream);
diff --git a/malloc/malloc.c b/malloc/malloc.c
index 2527e25..54e406b 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -5397,7 +5397,8 @@ malloc_printerr (int action, const char *str, void *ptr, mstate ar_ptr)
     set_arena_corrupt (ar_ptr);
 
   if ((action & 5) == 5)
-    __libc_message (action & 2, "%s\n", str);
+    __libc_message ((action & 2) ? (do_abort | do_backtrace) : do_message,
+		    "%s\n", str);
   else if (action & 1)
     {
       char buf[2 * sizeof (uintptr_t) + 1];
@@ -5407,7 +5408,8 @@ malloc_printerr (int action, const char *str, void *ptr, mstate ar_ptr)
       while (cp > buf)
         *--cp = '0';
 
-      __libc_message (action & 2, "*** Error in `%s': %s: 0x%s ***\n",
+      __libc_message ((action & 2) ? (do_abort | do_backtrace) : do_message,
+		      "*** Error in `%s': %s: 0x%s ***\n",
                       __libc_argv[0] ? : "<unknown>", str, cp);
     }
   else if (action & 2)
diff --git a/sysdeps/posix/libc_fatal.c b/sysdeps/posix/libc_fatal.c
index b261963..25af8bd 100644
--- a/sysdeps/posix/libc_fatal.c
+++ b/sysdeps/posix/libc_fatal.c
@@ -64,7 +64,7 @@ struct str_list
 
 /* Abort with an error message.  */
 void
-__libc_message (int do_abort, const char *fmt, ...)
+__libc_message (enum __libc_message_action action, const char *fmt, ...)
 {
   va_list ap;
   int fd = -1;
@@ -140,7 +140,7 @@ __libc_message (int do_abort, const char *fmt, ...)
 
       written = WRITEV_FOR_FATAL (fd, iov, nlist, total);
 
-      if (do_abort)
+      if ((action & do_abort))
 	{
 	  total = ((total + 1 + GLRO(dl_pagesize) - 1)
 		   & ~(GLRO(dl_pagesize) - 1));
@@ -167,9 +167,10 @@ __libc_message (int do_abort, const char *fmt, ...)
 
   va_end (ap);
 
-  if (do_abort)
+  if ((action & do_abort))
     {
-      BEFORE_ABORT (do_abort, written, fd);
+      if ((action & do_backtrace))
+	BEFORE_ABORT (do_abort, written, fd);
 
       /* Kill the application.  */
       abort ();
@@ -182,6 +183,6 @@ __libc_fatal (const char *message)
 {
   /* The loop is added only to keep gcc happy.  */
   while (1)
-    __libc_message (1, "%s", message);
+    __libc_message (do_abort | do_backtrace, "%s", message);
 }
 libc_hidden_def (__libc_fatal)
-- 
2.9.4