unittest: Skip string test case for sizeof (src) > sizeof (dst)

coverity complains that the subject test may cause dst buffer overrun
problem and it is right. The problem is when __builtin_constant_p (n)
returns true, memcpy_s_inline skips all the errors checking and does the
copy blindly. Please see the code in memcpy_s_inline.

The fix is to skip the subject test when the aformentioned builtin function
returns true.

Type: fix

Signed-off-by: Steven Luong <sluong@cisco.com>
Change-Id: I50de91cc0c853a134b3bcf3b0cd8d45d7668b092

1 files changed, 13 insertions, 4 deletions

diff --git a/src/plugins/unittest/string_test.c b/src/plugins/unittest/string_test.c
index 5016a86ac82..95a95d78c1d 100644
--- a/src/plugins/unittest/string_test.c
+++ b/src/plugins/unittest/string_test.c
@@ -85,11 +85,20 @@ test_memcpy_s (vlib_main_t * vm, unformat_input_t * input)
     if (src[i] != dst[i])
       return -1;
 
-  /* Size fail */
-  err = memcpy_s (dst + 1, sizeof (dst) - 1, src, sizeof (src));
+  /*
+   * Size test: sizeof (src) > sizeof (dst)
+   * Skip this test when __builtin_constant_p (sizeof (src)) is true.
+   * This is because memcpy_s_inline skips all the errors checking when the
+   * the above buildin function returns true which may cause overrun problem
+   * for dst buffer if this test is executed.
+   */
+  if (__builtin_constant_p (sizeof (src)) == 0)
+    {
+      err = memcpy_s (dst + 1, sizeof (dst) - 1, src, sizeof (src));
 
-  if (err == EOK)
-    return -1;
+      if (err == EOK)
+	return -1;
+    }
 
   /* overlap fail */
   err = memcpy_s (dst, sizeof (dst), dst + 1, sizeof (dst) - 1);