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

mcgrof · torvalds · commit ac68b1b3b9c7 · 2018-03-09T16:40:02.000-08:00
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: d9c6a72 ("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>
diff --git 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;
 	}

Original file line number	Diff line number	Diff line change
`@@ -1141,7 +1141,7 @@ static struct kmod_test_device *register_test_dev_kmod(void)`
`1141`	`1141`	`mutex_lock(&reg_dev_mutex);`
`1142`	`1142`
`1143`	`1143`	`/* int should suffice for number of devices, test for wrap */`
`1144`		`- if (unlikely(num_test_devs + 1) < 0) {`
	`1144`	`+ if (num_test_devs + 1 == INT_MAX) {`
`1145`	`1145`	`pr_err("reached limit of number of test devices\n");`
`1146`	`1146`	`goto out;`
`1147`	`1147`	`}`