linux-kernel - [PATCH 4.14 240/496] lib/test_kmod.c: fix limit check on number of test devices created

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Date:   Mon, 28 May 2018 12:00:25 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Dan Carpenter <dan.carpenter@...cle.com>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: [PATCH 4.14 240/496] lib/test_kmod.c: fix limit check on number of test devices created

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: "Luis R. Rodriguez" <mcgrof@...nel.org>

[ Upstream commit ac68b1b3b9c73e652dc7ce0585672e23c5a2dca4 ]

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.

Link: http://lkml.kernel.org/r/20180224030046.24238-1-mcgrof@kernel.org
Fixes: d9c6a72d6fa2 ("kmod: add test driver to stress test the module loader")
Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Luis R. Rodriguez <mcgrof@...nel.org>
Acked-by: Kees Cook <keescook@...omium.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 lib/test_kmod.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/lib/test_kmod.c
+++ b/lib/test_kmod.c
@@ -1149,7 +1149,7 @@ static struct kmod_test_device *register
 	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;
 	}