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

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Date:   Fri, 23 Feb 2018 19:00:46 -0800
From:   "Luis R. Rodriguez" <mcgrof@...nel.org>
To:     akpm@...ux-foundation.org
Cc:     keescook@...omium.org, dmitry.torokhov@...il.com, jeyu@...hat.com,
        rusty@...tcorp.com.au, mmarek@...e.com, pmladek@...e.com,
        mbenes@...e.cz, jpoimboe@...hat.com, linux@...ck-us.net,
        ebiederm@...ssion.com, matt.redfearn@...tec.com,
        dan.carpenter@...cle.com, colin.king@...onical.com,
        danielmentz@...gle.com, dcb314@...mail.com,
        gregkh@...uxfoundation.org, torvalds@...ux-foundation.org,
        linux-kernel@...r.kernel.org,
        "Luis R. Rodriguez" <mcgrof@...nel.org>
Subject: [PATCH] test_kmod: fix limit check on number of test devices created

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@...cle.com>
Fixes: d9c6a72d6fa2 ("kmod: add test driver to stress test the module loader")
Signed-off-by: Luis R. Rodriguez <mcgrof@...nel.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