[PATCH] test_kmod: fix limit check on number of test devices created

[PATCH] test_kmod: fix limit check on number of test devices created

[Luis R. Rodriguez]

As reported by Dan the parentheses is in the wrong place, and since
unlikely() call returns either 0 or 1 it's never less than zero.
The second issue is that signed integer overflows like "INT_MAX + 1" are
undefined behavior.

Since num_test_devs represents the number of devices, we want to stop
prior to hitting the max, and not rely on the wrap arround at all. So
just cap at num_test_devs + 1, prior to assigning a new device.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: d9c6a72d6fa2 ("kmod: add test driver to stress test the module loader")
Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
---
 lib/test_kmod.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/test_kmod.c b/lib/test_kmod.c
index e372b97eee13..0e5b7a61460b 100644
--- a/lib/test_kmod.c
+++ b/lib/test_kmod.c
@@ -1141,7 +1141,7 @@ static struct kmod_test_device *register_test_dev_kmod(void)
 	mutex_lock(&reg_dev_mutex);
 
 	/* int should suffice for number of devices, test for wrap */
-	if (unlikely(num_test_devs + 1) < 0) {
+	if (num_test_devs + 1 == INT_MAX) {
 		pr_err("reached limit of number of test devices\n");
 		goto out;
 	}
-- 
2.16.2

Re: [PATCH] test_kmod: fix limit check on number of test devices created

[Kees Cook]

On Fri, Feb 23, 2018 at 7:00 PM, Luis R. Rodriguez <mcgrof@kernel.org> wrote:
> As reported by Dan the parentheses is in the wrong place, and since
> unlikely() call returns either 0 or 1 it's never less than zero.
> The second issue is that signed integer overflows like "INT_MAX + 1" are
> undefined behavior.
>
> Since num_test_devs represents the number of devices, we want to stop
> prior to hitting the max, and not rely on the wrap arround at all. So
> just cap at num_test_devs + 1, prior to assigning a new device.
>
> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
> Fixes: d9c6a72d6fa2 ("kmod: add test driver to stress test the module loader")
> Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>

Acked-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
>  lib/test_kmod.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/lib/test_kmod.c b/lib/test_kmod.c
> index e372b97eee13..0e5b7a61460b 100644
> --- a/lib/test_kmod.c
> +++ b/lib/test_kmod.c
> @@ -1141,7 +1141,7 @@ static struct kmod_test_device *register_test_dev_kmod(void)
>         mutex_lock(&reg_dev_mutex);
>
>         /* int should suffice for number of devices, test for wrap */
> -       if (unlikely(num_test_devs + 1) < 0) {
> +       if (num_test_devs + 1 == INT_MAX) {
>                 pr_err("reached limit of number of test devices\n");
>                 goto out;
>         }
> --
> 2.16.2
>



-- 
Kees Cook
Pixel Security