CVE-2012-3406: Stack overflow in vfprintf [BZ #16617]

A larger number of format specifiers coudld cause a stack overflow,
potentially allowing to bypass _FORTIFY_SOURCE format string
protection.

stdio-common/bug23-3.c

@@ -0,0 +1,50 @@
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+
+int
+do_test (void)
+{
+  size_t instances = 16384;
+#define X0 "\n%1$s\n" "%1$s" "%2$s" "%2$s" "%3$s" "%4$s" "%5$d" "%5$d"
+  const char *item = "\na\nabbcd55";
+#define X3 X0 X0 X0 X0 X0 X0 X0 X0
+#define X6 X3 X3 X3 X3 X3 X3 X3 X3
+#define X9 X6 X6 X6 X6 X6 X6 X6 X6
+#define X12 X9 X9 X9 X9 X9 X9 X9 X9
+#define X14 X12 X12 X12 X12
+#define TRAILER "%%%%%%%%%%%%%%%%%%%%%%%%%%"
+#define TRAILER2 TRAILER TRAILER
+  size_t length = instances * strlen (item) + strlen (TRAILER) + 1;
+
+  char *buf = malloc (length + 1);
+  snprintf (buf, length + 1,
+	    X14 TRAILER2 "\n",
+	    "a", "b", "c", "d", 5);
+
+  const char *p = buf;
+  size_t i;
+  for (i = 0; i < instances; ++i)
+    {
+      const char *expected;
+      for (expected = item; *expected; ++expected)
+	{
+	  if (*p != *expected)
+	    {
+	      printf ("mismatch at offset %zu (%zu): expected %d, got %d\n",
+		      (size_t) (p - buf), i, *expected & 0xFF, *p & 0xFF);
+	      return 1;
+	    }
+	  ++p;
+	}
+    }
+  if (strcmp (p, TRAILER "\n") != 0)
+    {
+      printf ("mismatch at trailer: [%s]\n", p);
+      return 1;
+    }
+  free (buf);
+  return 0;
+}
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"