* [PATCH] lib/test_kmod: Fix an integer overflow test
@ 2018-01-22 10:27 Dan Carpenter
2018-02-24 2:59 ` Luis R. Rodriguez
0 siblings, 1 reply; 5+ messages in thread
From: Dan Carpenter @ 2018-01-22 10:27 UTC (permalink / raw)
To: Luis R. Rodriguez; +Cc: linux-kernel, kernel-janitors
The main problem is that the parentheses are in the wrong place and the
unlikely() call returns either 0 or 1 so it's never less than zero. The
other problem is that signed integer overflows like "INT_MAX + 1" are
undefined behavior.
Fixes: d9c6a72d6fa2 ("kmod: add test driver to stress test the module loader")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
diff --git a/lib/test_kmod.c b/lib/test_kmod.c
index e372b97eee13..30fd6d9e5361 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(®_dev_mutex);
/* int should suffice for number of devices, test for wrap */
- if (unlikely(num_test_devs + 1) < 0) {
+ if (num_test_devs == INT_MAX) {
pr_err("reached limit of number of test devices\n");
goto out;
}
^ permalink raw reply related [flat|nested] 5+ messages in thread* Re: [PATCH] lib/test_kmod: Fix an integer overflow test 2018-01-22 10:27 [PATCH] lib/test_kmod: Fix an integer overflow test Dan Carpenter @ 2018-02-24 2:59 ` Luis R. Rodriguez 2018-02-24 8:45 ` Dan Carpenter 0 siblings, 1 reply; 5+ messages in thread From: Luis R. Rodriguez @ 2018-02-24 2:59 UTC (permalink / raw) To: Dan Carpenter; +Cc: Luis R. Rodriguez, linux-kernel, kernel-janitors, cocci On Mon, Jan 22, 2018 at 01:27:54PM +0300, Dan Carpenter wrote: > The main problem is that the parentheses are in the wrong place and the > unlikely() call returns either 0 or 1 so it's never less than zero. Doh, thanks, yes. Seems worth considering a grammar rule for it. > The other problem is that signed integer overflows like "INT_MAX + 1" are > undefined behavior. Likewise. This seems like another possible generic typo issue. But I would not resolve it the way you did, in this particular case below num_test_devs represents the number of already registered devs, before we increment. So the way to resolve this would be: if (num_test_devs + 1 == INT_MAX) I'll get this upstream, thanks! Luis > Fixes: d9c6a72d6fa2 ("kmod: add test driver to stress test the module loader") > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com> > > diff --git a/lib/test_kmod.c b/lib/test_kmod.c > index e372b97eee13..30fd6d9e5361 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(®_dev_mutex); > > /* int should suffice for number of devices, test for wrap */ > - if (unlikely(num_test_devs + 1) < 0) { > + if (num_test_devs == INT_MAX) { > pr_err("reached limit of number of test devices\n"); > goto out; > } > -- Luis Rodriguez, SUSE LINUX GmbH Maxfeldstrasse 5; D-90409 Nuernberg ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] lib/test_kmod: Fix an integer overflow test 2018-02-24 2:59 ` Luis R. Rodriguez @ 2018-02-24 8:45 ` Dan Carpenter 2018-02-24 22:06 ` Luis R. Rodriguez 0 siblings, 1 reply; 5+ messages in thread From: Dan Carpenter @ 2018-02-24 8:45 UTC (permalink / raw) To: Luis R. Rodriguez; +Cc: linux-kernel, kernel-janitors, cocci On Sat, Feb 24, 2018 at 02:59:41AM +0000, Luis R. Rodriguez wrote: > On Mon, Jan 22, 2018 at 01:27:54PM +0300, Dan Carpenter wrote: > > The main problem is that the parentheses are in the wrong place and the > > unlikely() call returns either 0 or 1 so it's never less than zero. > > Doh, thanks, yes. Seems worth considering a grammar rule for it. > > > The other problem is that signed integer overflows like "INT_MAX + 1" are > > undefined behavior. > > Likewise. > > This seems like another possible generic typo issue. But I would not resolve it > the way you did, in this particular case below num_test_devs represents the > number of already registered devs, before we increment. So the way to resolve > this would be: > > if (num_test_devs + 1 == INT_MAX) > > I'll get this upstream, thanks! There is no issue if num_test_devs is INT_MAX. But capping it at INT_MAX - 1 is also fine. regards, dan carpenter ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] lib/test_kmod: Fix an integer overflow test 2018-02-24 8:45 ` Dan Carpenter @ 2018-02-24 22:06 ` Luis R. Rodriguez 2018-02-24 23:34 ` Dan Carpenter 0 siblings, 1 reply; 5+ messages in thread From: Luis R. Rodriguez @ 2018-02-24 22:06 UTC (permalink / raw) To: Dan Carpenter; +Cc: Luis R. Rodriguez, linux-kernel, kernel-janitors, cocci On Sat, Feb 24, 2018 at 11:45:16AM +0300, Dan Carpenter wrote: > On Sat, Feb 24, 2018 at 02:59:41AM +0000, Luis R. Rodriguez wrote: > > On Mon, Jan 22, 2018 at 01:27:54PM +0300, Dan Carpenter wrote: > > > The main problem is that the parentheses are in the wrong place and the > > > unlikely() call returns either 0 or 1 so it's never less than zero. > > > > Doh, thanks, yes. Seems worth considering a grammar rule for it. > > > > > The other problem is that signed integer overflows like "INT_MAX + 1" are > > > undefined behavior. > > > > Likewise. > > > > This seems like another possible generic typo issue. But I would not resolve it > > the way you did, in this particular case below num_test_devs represents the > > number of already registered devs, before we increment. So the way to resolve > > this would be: > > > > if (num_test_devs + 1 == INT_MAX) > > > > I'll get this upstream, thanks! > > There is no issue if num_test_devs is INT_MAX. But capping it at > INT_MAX - 1 is also fine. If num_test_devs is INT_MAX, then doing num_test_devs + 1 overflows and as you noted that is undefined? Luis ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] lib/test_kmod: Fix an integer overflow test 2018-02-24 22:06 ` Luis R. Rodriguez @ 2018-02-24 23:34 ` Dan Carpenter 0 siblings, 0 replies; 5+ messages in thread From: Dan Carpenter @ 2018-02-24 23:34 UTC (permalink / raw) To: Luis R. Rodriguez; +Cc: linux-kernel, kernel-janitors, cocci On Sat, Feb 24, 2018 at 10:06:01PM +0000, Luis R. Rodriguez wrote: > On Sat, Feb 24, 2018 at 11:45:16AM +0300, Dan Carpenter wrote: > > On Sat, Feb 24, 2018 at 02:59:41AM +0000, Luis R. Rodriguez wrote: > > > On Mon, Jan 22, 2018 at 01:27:54PM +0300, Dan Carpenter wrote: > > > > The main problem is that the parentheses are in the wrong place and the > > > > unlikely() call returns either 0 or 1 so it's never less than zero. > > > > > > Doh, thanks, yes. Seems worth considering a grammar rule for it. > > > > > > > The other problem is that signed integer overflows like "INT_MAX + 1" are > > > > undefined behavior. > > > > > > Likewise. > > > > > > This seems like another possible generic typo issue. But I would not resolve it > > > the way you did, in this particular case below num_test_devs represents the > > > number of already registered devs, before we increment. So the way to resolve > > > this would be: > > > > > > if (num_test_devs + 1 == INT_MAX) > > > > > > I'll get this upstream, thanks! > > > > There is no issue if num_test_devs is INT_MAX. But capping it at > > INT_MAX - 1 is also fine. > > If num_test_devs is INT_MAX, then doing num_test_devs + 1 overflows > and as you noted that is undefined? If it's INT_MAX we never do "num_test_devs + 1", we return a NULL. regards, dan carpenter ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2018-02-24 23:34 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2018-01-22 10:27 [PATCH] lib/test_kmod: Fix an integer overflow test Dan Carpenter 2018-02-24 2:59 ` Luis R. Rodriguez 2018-02-24 8:45 ` Dan Carpenter 2018-02-24 22:06 ` Luis R. Rodriguez 2018-02-24 23:34 ` Dan Carpenter
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