[PATCH][BZ #1349] Return requested size for malloc_usable_size whenMALLOC_CHECK_ > 0

[Siddhesh Poyarekar <siddhesh at redhat dot com>]

Hi,

malloc_usable_size returns the usable size in an allocated chunk, which
may be >= the requested size. In the case of MALLOC_CHECK_ being
exported to > 0 however, only the requested size is usable, since a
magic value is written at the end of the request size to trap writes
beyond request bounds. Hence, when MALLOC_CHECK_ is exported to > 0,
malloc_usable_size() should return the request size. The attached patch
does exactly that.

There is also a test case included in the patch to verify that the
problem is fixed. I have verified on Fedora-16 x86_64 that this does
not cause any regressions.

Regards,
Siddhesh

ChangeLog:

	* malloc/Makefile (tests): Add tst-malloc-usable test case.
	(tst-malloc-usable-ENV): Set environment for test case.
	* malloc/hooks.c (malloc_check_get_size): New function to get
	requested size.
	* malloc/malloc.c (musable): Use malloc_check_get_size.
	* malloc/tst-malloc-usable.c: New test case.

diff --git a/NEWS b/NEWS
index b2800e2..2b01340 100644
--- a/NEWS
+++ b/NEWS
@@ -9,10 +9,10 @@ Version 2.17
 
 * The following bugs are resolved with this release:
 
-  3479, 5400, 6778, 6808, 9685, 11607, 13717, 13696, 13939, 14042, 14090,
-  14166, 14150, 14151, 14154, 14157, 14166, 14173, 14195, 14252, 14283,
-  14298, 14303, 14307, 14328, 14331, 14336, 14337, 14347, 14349, 14459,
-  14476, 14505, 14516, 14519
+  1349, 3479, 5400, 6778, 6808, 9685, 11607, 13717, 13696, 13939, 14042,
+  14090, 14166, 14150, 14151, 14154, 14157, 14166, 14173, 14195, 14252,
+  14283, 14298, 14303, 14307, 14328, 14331, 14336, 14337, 14347, 14349,
+  14459, 14476, 14505, 14516, 14519
 
 * Support for STT_GNU_IFUNC symbols added for s390 and s390x.
   Optimized versions of memcpy, memset, and memcmp added for System z10 and
diff --git a/malloc/Makefile b/malloc/Makefile
index 5d6d716..55c675b 100644
--- a/malloc/Makefile
+++ b/malloc/Makefile
@@ -1,5 +1,4 @@
-# Copyright (C) 1991-2003, 2005, 2006, 2007, 2009, 2011, 2012
-# Free Software Foundation, Inc.
+# Copyright (C) 1991-2012 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
@@ -26,7 +25,7 @@ all:
 dist-headers := malloc.h
 headers := $(dist-headers) obstack.h mcheck.h
 tests := mallocbug tst-malloc tst-valloc tst-calloc tst-obstack \
-	 tst-mallocstate tst-mcheck tst-mallocfork tst-trim1
+	 tst-mallocstate tst-mcheck tst-mallocfork tst-trim1 tst-malloc-usable
 test-srcs = tst-mtrace
 
 routines = malloc morecore mcheck mtrace obstack
@@ -116,6 +115,7 @@ endif
 endif
 
 tst-mcheck-ENV = MALLOC_CHECK_=3
+tst-malloc-usable-ENV = MALLOC_CHECK_=3
 
 CPPFLAGS-malloc.c += -DPER_THREAD
 # Uncomment this for test releases.  For public releases it is too expensive.
diff --git a/malloc/hooks.c b/malloc/hooks.c
index 8a34c78..b38dffb 100644
--- a/malloc/hooks.c
+++ b/malloc/hooks.c
@@ -1,5 +1,5 @@
 /* Malloc implementation for multiple threads without lock contention.
-   Copyright (C) 2001-2009, 2011, 2012 Free Software Foundation, Inc.
+   Copyright (C) 2001-2012 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Wolfram Gloger <wg@malloc.de>, 2001.
 
@@ -89,6 +89,35 @@ __malloc_check_init()
 
 #define MAGICBYTE(p) ( ( ((size_t)p >> 3) ^ ((size_t)p >> 11)) & 0xFF )
 
+/* Visualize the chunk as being partitioned into blocks of 256 bytes from the
+   highest address of the chunk, downwards.  The beginning of each block tells
+   us the size of the previous block, up to the actual size of the requested
+   memory.  Our magic byte is right at the end of the requested size, so we
+   must reach it with this iteration, otherwise we have witnessed a memory
+   corruption.  */
+static size_t
+malloc_check_get_size(mchunkptr p)
+{
+  size_t size;
+  unsigned char c;
+  unsigned char magic = MAGICBYTE(p);
+
+  assert(using_malloc_checking == 1);
+
+  for (size = chunksize(p) - 1 + (chunk_is_mmapped(p) ? 0 : SIZE_SZ);
+       (c = ((unsigned char*)p)[size]) != magic;
+       size -= c) {
+    if(c<=0 || size<(c+2*SIZE_SZ)) {
+      malloc_printerr(check_action, "malloc_check_get_size: memory corruption",
+		      chunk2mem(p));
+      return 0;
+    }
+  }
+
+  /* chunk2mem size.  */
+  return size - 2*SIZE_SZ;
+}
+
 /* Instrument a chunk with overrun detector byte(s) and convert it
    into a user pointer with requested size sz. */
 
diff --git a/malloc/malloc.c b/malloc/malloc.c
index 0f1796c..bd562df 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -1,5 +1,5 @@
 /* Malloc implementation for multiple threads without lock contention.
-   Copyright (C) 1996-2009, 2010, 2011, 2012 Free Software Foundation, Inc.
+   Copyright (C) 1996-2012 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Wolfram Gloger <wg@malloc.de>
    and Doug Lea <dl@cs.oswego.edu>, 2001.
@@ -4563,6 +4563,9 @@ musable(void* mem)
   mchunkptr p;
   if (mem != 0) {
     p = mem2chunk(mem);
+
+    if (__builtin_expect(using_malloc_checking == 1, 0))
+      return malloc_check_get_size(p);
     if (chunk_is_mmapped(p))
       return chunksize(p) - 2*SIZE_SZ;
     else if (inuse(p))
diff --git a/malloc/tst-malloc-usable.c b/malloc/tst-malloc-usable.c
new file mode 100644
index 0000000..103298b
--- /dev/null
+++ b/malloc/tst-malloc-usable.c
@@ -0,0 +1,40 @@
+/* Ensure that malloc_usable_size returns the request size with
+   MALLOC_CHECK_ exported to a positive value.
+
+   Copyright (C) 2012 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 <malloc.h>
+#include <string.h>
+#include <stdio.h>
+
+static int
+do_test (void)
+{
+  void *p = malloc (7);
+  if (!p)
+    {
+      printf ("memory allocation failed\n");
+      return 1;
+    }
+  memset (p, 0, malloc_usable_size (p));
+  free (p);
+  return 0;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"