Fix for test "malloc_usable_size: expected 7 but got 11"

[BZ #17581] The checking chain of unused chunks was terminated by a hash of
the block pointer, which was sometimes confused with the chunk length byte.
The chain is now terminated by a NULL byte.

3 files changed, 54 insertions, 37 deletions

diff --git a/ChangeLog b/ChangeLog
index 613f304ddc..7d588335ae 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2014-12-01  James Lemke  <jwlemke@codesourcery.com>
+
+	[BZ #17581]
+	* malloc/hooks.c
+	(mem2mem_check): Add a terminator to the chain of checking blocks.
+	(malloc_check_get_size): Use it here.
+	(mem2chunk_check): Ditto.
+
 2014-12-01  Rajalakshmi Srinivasaraghavan <raji@linux.vnet.ibm.com>
 
 	* sysdeps/powerpc/powerpc64/strtok.S: New file.
diff --git a/NEWS b/NEWS
index e1f2342bdc..5450e8e0d1 100644
--- a/NEWS
+++ b/NEWS
@@ -12,8 +12,8 @@ Version 2.21
   6652, 12926, 13862, 14132, 14138, 14171, 14498, 15215, 15884, 16469,
   16619, 16740, 16857, 17192, 17266, 17344, 17363, 17370, 17371, 17411,
   17460, 17475, 17485, 17501, 17506, 17508, 17522, 17555, 17570, 17571,
-  17572, 17573, 17574, 17582, 17583, 17584, 17585, 17589, 17594, 17608,
-  17616, 17625, 17633.
+  17572, 17573, 17574, 17581, 17582, 17583, 17584, 17585, 17589, 17594,
+  17608, 17616, 17625, 17633.
 
 * CVE-2104-7817 The wordexp function could ignore the WRDE_NOCMD flag
   under certain input conditions resulting in the execution of a shell for
diff --git a/malloc/hooks.c b/malloc/hooks.c
index 00ee6bec8c..996111a7e3 100644
--- a/malloc/hooks.c
+++ b/malloc/hooks.c
@@ -90,31 +90,35 @@ __malloc_check_init (void)
 
 #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.  */
+/* Visualize the chunk as being partitioned into blocks of 255 bytes from the
+   highest address of the chunk, downwards.  The end of each block tells us
+   the size of that block, up to the actual size of the requested memory.
+   The last block has a length of zero and is followed by the magic byte.
+   Our magic byte is right at the end of the requested size.  If we don't
+   reach it with this iteration we have witnessed a memory corruption.  */
 static size_t
 malloc_check_get_size (mchunkptr p)
 {
-  size_t size;
+  size_t total_sz, 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;
+  /* Validate the length-byte chain.  */
+  total_sz = chunksize (p) + (chunk_is_mmapped (p) ? 0 : SIZE_SZ);
+  for (size = total_sz - 1;
+       (c = ((unsigned char *) p)[size]) != 0;
        size -= c)
     {
-      if (c <= 0 || size < (c + 2 * SIZE_SZ))
-        {
-          malloc_printerr (check_action, "malloc_check_get_size: memory corruption",
-                           chunk2mem (p));
-          return 0;
-        }
+      if (size <= c + 2 * SIZE_SZ)
+	break;
+    }
+  if (c != 0 || ((unsigned char *) p)[--size] != magic)
+    {
+      malloc_printerr (check_action, "malloc_check_get_size: memory corruption",
+		       chunk2mem (p));
+      return 0;
     }
 
   /* chunk2mem size.  */
@@ -130,22 +134,24 @@ mem2mem_check (void *ptr, size_t sz)
 {
   mchunkptr p;
   unsigned char *m_ptr = ptr;
-  size_t i;
+  size_t user_sz, block_sz, i;
 
   if (!ptr)
     return ptr;
 
   p = mem2chunk (ptr);
-  for (i = chunksize (p) - (chunk_is_mmapped (p) ? 2 * SIZE_SZ + 1 : SIZE_SZ + 1);
-       i > sz;
-       i -= 0xFF)
+  user_sz = chunksize (p) + (chunk_is_mmapped (p) ? 0 : SIZE_SZ);
+  user_sz -= 2 * SIZE_SZ;
+  for (i = user_sz - 1; i > sz; i -= block_sz)
     {
-      if (i - sz < 0x100)
-        {
-          m_ptr[i] = (unsigned char) (i - sz);
-          break;
-        }
-      m_ptr[i] = 0xFF;
+      block_sz = i - (sz + 1);
+      if (block_sz > 0xff)
+	block_sz = 0xff;
+
+      m_ptr[i] = (unsigned char) block_sz;
+
+      if (block_sz == 0)
+	break;
     }
   m_ptr[sz] = MAGICBYTE (p);
   return (void *) m_ptr;
@@ -166,11 +172,12 @@ mem2chunk_check (void *mem, unsigned char **magic_p)
     return NULL;
 
   p = mem2chunk (mem);
+  sz = chunksize (p);
+  magic = MAGICBYTE (p);
   if (!chunk_is_mmapped (p))
     {
       /* Must be a chunk in conventional heap memory. */
       int contig = contiguous (&main_arena);
-      sz = chunksize (p);
       if ((contig &&
            ((char *) p < mp_.sbrk_base ||
             ((char *) p + sz) >= (mp_.sbrk_base + main_arena.system_mem))) ||
@@ -180,12 +187,13 @@ mem2chunk_check (void *mem, unsigned char **magic_p)
                                next_chunk (prev_chunk (p)) != p)))
         return NULL;
 
-      magic = MAGICBYTE (p);
-      for (sz += SIZE_SZ - 1; (c = ((unsigned char *) p)[sz]) != magic; sz -= c)
+      for (sz += SIZE_SZ - 1; (c = ((unsigned char *) p)[sz]) != 0; sz -= c)
         {
-          if (c <= 0 || sz < (c + 2 * SIZE_SZ))
-            return NULL;
+	  if (sz <= c + 2 * SIZE_SZ)
+	    break;
         }
+      if (c != 0 || ((unsigned char *) p)[--sz] != magic)
+	return NULL;
     }
   else
     {
@@ -201,15 +209,16 @@ mem2chunk_check (void *mem, unsigned char **magic_p)
            offset < 0x2000) ||
           !chunk_is_mmapped (p) || (p->size & PREV_INUSE) ||
           ((((unsigned long) p - p->prev_size) & page_mask) != 0) ||
-          ((sz = chunksize (p)), ((p->prev_size + sz) & page_mask) != 0))
+          ((p->prev_size + sz) & page_mask) != 0)
         return NULL;
 
-      magic = MAGICBYTE (p);
-      for (sz -= 1; (c = ((unsigned char *) p)[sz]) != magic; sz -= c)
+      for (sz -= 1; (c = ((unsigned char *) p)[sz]) != 0; sz -= c)
         {
-          if (c <= 0 || sz < (c + 2 * SIZE_SZ))
-            return NULL;
+	  if (sz <= c + 2 * SIZE_SZ)
+	    break;
         }
+      if (c != 0 || ((unsigned char *) p)[--sz] != magic)
+	return NULL;
     }
   ((unsigned char *) p)[sz] ^= 0xFF;
   if (magic_p)