From: Chenyuan Yang <chenyuan0y@gmail.com>
To: John Hubbard <jhubbard@nvidia.com>
Cc: Matthew Wilcox <willy@infradead.org>,
akpm@linux-foundation.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, syzkaller@googlegroups.com,
Zijie Zhao <zzjas98@gmail.com>
Subject: Re: [Linux Kernel Bug][mm/gup] 3 Warning Crashes: kmalloc bug in gup_test_ioctl, is_valid_gup_args, pin_user_pages_fast
Date: Fri, 26 Jan 2024 13:23:46 -0600 [thread overview]
Message-ID: <CALGdzuqfyB66WvWiZWTqB4Nx1+vS04R2tq8Nu08OFzsggipDmg@mail.gmail.com> (raw)
In-Reply-To: <46490518-0cdb-4d11-be9a-374ed5792da8@nvidia.com>
Hello John and Matthew,
Thanks a lot for your further explanation of this issue! It really
helps me have a deeper understanding of the testing interface used in
the kernel.
Best,
Chenyuan
On Fri, Jan 26, 2024 at 1:09 PM John Hubbard <jhubbard@nvidia.com> wrote:
>
> On 1/26/24 10:34, Matthew Wilcox wrote:
> > On Fri, Jan 26, 2024 at 11:31:26AM -0600, Chenyuan Yang wrote:
> >> In this context, I would like to seek your valued opinion. Do you
> >> believe it would be more prudent to avoid fuzz testing the
> >> `gup_test_ioctl`, or are the warnings in `gup_test_ioctl` an
> >> anticipated outcome?
> >
> > It seems like a waste of time. Debian certainly disables it, so
> > unless you can find a distro who enables it, I wouldn't bother.
>
> +1000! The purpose of gup_test_ioctl is to provide a way to invoke,
> from user space, direct testing of some kernel interfaces that are
> not actually exposed to user space for production systems.
>
> Fuzzing this interface is exactly what you should never do. :)
>
> >
> >> It seems that `gup_test_ioctl` can indeed be exposed in the kernel by
> >> accessing /sys/kernel/debug/gup_test.
>
> That's a debug interface.
>
> >
> > If someone wants to fix these things, they can, but it just doesn't
> > seem worth doing. Part of the art of fuzz testing is finding things
> > that are worth testing.
>
> I'll go just slightly further, even: some conceivable "fixes" could end
> up hurting test coverage. Without providing any real benefit.
>
>
> thanks,
> --
> John Hubbard
> NVIDIA
>
>
prev parent reply other threads:[~2024-01-26 19:24 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-26 17:04 [Linux Kernel Bug][mm/gup] 3 Warning Crashes: kmalloc bug in gup_test_ioctl, is_valid_gup_args, pin_user_pages_fast Chenyuan Yang
2024-01-26 17:11 ` Matthew Wilcox
2024-01-26 17:31 ` Chenyuan Yang
2024-01-26 18:34 ` Matthew Wilcox
2024-01-26 19:08 ` John Hubbard
2024-01-26 19:23 ` Chenyuan Yang [this message]
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