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From: Chenyuan Yang <chenyuan0y@gmail.com>
Date: Fri, 26 Jan 2024 11:31:26 -0600
Message-ID: <CALGdzuo7V-3-US9U+rjyBfmZD=d-gUfAxJejsTUsmnSZNDnh5A@mail.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
To: Matthew Wilcox <willy@infradead.org>
Cc: akpm@linux-foundation.org, linux-mm@kvack.org, 
	linux-kernel@vger.kernel.org, syzkaller@googlegroups.com, 
	Zijie Zhao <zzjas98@gmail.com>, John Hubbard <jhubbard@nvidia.com>
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Hello Matthew,

Thanks very much for your prompt response!

For `gup_test_ioctl`, we generate the descriptions for it for
interaction and testing:
```
openat$gup_test(fd const[AT_FDCWD], file ptr[in,
string["/sys/kernel/debug/gup_test"]], flags const[O_RDWR], mode
const[0]) fd_gup_test
ioctl$PIN_FAST_BENCHMARK(fd fd_gup_test, cmd
const[PIN_FAST_BENCHMARK], arg ptr[inout, gup_test])
..
gup_test {
    ...
    gup_flags int32
    ...
}
```

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 that `gup_test_ioctl` can indeed be exposed in the kernel by
accessing /sys/kernel/debug/gup_test.

Thank you once again for your time and expertise.

Best,
Chenyuan

On Fri, Jan 26, 2024 at 11:11=E2=80=AFAM Matthew Wilcox <willy@infradead.or=
g> wrote:
>
> On Fri, Jan 26, 2024 at 11:04:53AM -0600, Chenyuan Yang wrote:
> > Dear Developers for Linux Memory Management,
> >
> > We encountered 3 warning crashes when testing the memory management
> > with Syzkaller and our generated specifications:
>
> These all come in through gup_test_ioctl().  It's my impression
> that this is something you can enable to wreak havoc on your kernel
> and it's not something which should ever be exposed to fuzzers.
>
>
>
>
>