lib/test_kmod.c: fix limit check on number of test devices created

BugLink: http://bugs.launchpad.net/bugs/1786352
[ 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@oracle.com>
Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/lib/test_kmod.c b/lib/test_kmod.c
index e372b97eee1301c1bd2e6c49b49e57c8ef4bff10..0e5b7a61460bb092226a3785abeaa2168d95d790 100644 (file)
--- 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;
        }