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From: "Luis R. Rodriguez" <mcgrof@kernel.org>
To: akpm@linux-foundation.org
Cc: keescook@chromium.org, dmitry.torokhov@gmail.com,
	jeyu@redhat.com, rusty@rustcorp.com.au, mmarek@suse.com,
	pmladek@suse.com, mbenes@suse.cz, jpoimboe@redhat.com,
	linux@roeck-us.net, ebiederm@xmission.com,
	matt.redfearn@imgtec.com, dan.carpenter@oracle.com,
	colin.king@canonical.com, danielmentz@google.com,
	dcb314@hotmail.com, gregkh@linuxfoundation.org,
	torvalds@linux-foundation.org, linux-kernel@vger.kernel.org,
	"Luis R. Rodriguez" <mcgrof@kernel.org>
Subject: [PATCH] test_kmod: fix limit check on number of test devices created
Date: Fri, 23 Feb 2018 19:00:46 -0800
Message-ID: <20180224030046.24238-1-mcgrof@kernel.org> (raw)

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

             reply index

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-24  3:00 Luis R. Rodriguez [this message]
2018-02-27 23:24 ` Kees Cook

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