Re: [PATH] [BZ 15674] Fix reading past the array boundary in __memcmp_ssse3

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

On Wed, Jun 26, 2013 at 2:03 PM, Roland McGrath <roland@hack.frob.com> wrote:
> I don't know why the BUF variable is there rather than just using BUF2
> directly as you do BUF1.

BUF2 also works.

> It seems a little nasty that it repeats the magic number from test-string.h
> and relies on it matching for the test to be correct.  If tests are going
> to encode the particular values of the BUF[12] fill bytes, then test-string.h
> should define macros for the values so we don't repeat the constants.
>
> OTOH, the new test could just memcpy instead of memset to more
> straightforwardly ensure the buffers match where they should and don't
> where they shouldn't:
>
>         memcpy (buf2, buf1, page_size);
>         ((char *) buf2)[page_size - 1] ^= 0x11;
>

It should work.

--
H.J.
--
diff --git a/string/test-memcmp.c b/string/test-memcmp.c
index b30e34d..0420cd0 100644
--- a/string/test-memcmp.c
+++ b/string/test-memcmp.c
@@ -448,6 +448,29 @@ check1 (void)
     }
 }

+/* This test checks that memcmp doesn't overrun buffers.  */
+static void
+check2 (void)
+{
+  size_t max_length = page_size / sizeof (CHAR);
+
+  /* Initialize buf2 to the same values as buf1.  The bug requires the
+     last compared byte to be different.  */
+  memcpy (buf2, buf1, page_size);
+  ((char *) buf2)[page_size - 1] ^= 0x11;
+
+  for (size_t length = 1; length < max_length; length++)
+    {
+      CHAR *s1 = (CHAR *) buf1 + max_length - length;
+      CHAR *s2 = (CHAR *) buf2 + max_length - length;
+
+      const int exp_result = SIMPLE_MEMCMP (s1, s2, length);
+
+      FOR_EACH_IMPL (impl, 0)
+    check_result (impl, s1, s2, length, exp_result);
+    }
+}
+
 int
 test_main (void)
 {
@@ -456,6 +479,7 @@ test_main (void)
   test_init ();

   check1 ();
+  check2 ();

   printf ("%23s", "");
   FOR_EACH_IMPL (impl, 0)