If arguments are consumed without output when encountering %n, it
could be used to benefit or improve information leak attacks that were
exposed via a limited size buffer. Since %n is not used by the kernel,
there is no reason to make an info leak attack any easier.
Signed-off-by: Kees Cook <keesc...@chromium.org>
Cc: sta...@vger.kernel.org # 3.13+
---
lib/vsprintf.c | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 185b6d300ebc..9d5c48b705f9 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1735,14 +1735,10 @@ int vsnprintf(char *buf, size_t size, const char *fmt,
va_list args)
case FORMAT_TYPE_NRCHARS: {
/*
* Since %n poses a greater security risk than
- * utility, ignore %n and skip its argument.
+ * utility, it should not be implemented. Instead,
+ * when encountering %n, ignore the arguments.
*/
- void *skip_arg;
-
- WARN_ONCE(1, "Please remove ignored %%n in '%s'\n",
- old_fmt);
-
- skip_arg = va_arg(args, void *);
+ WARN_ONCE(1, "Ignored %%n in '%s'\n", old_fmt);
break;
}
--
1.7.9.5
--
Kees Cook
Chrome OS Security
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
