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Fri, 26 Jan 2024 11:23:57 -0800 (PST) MIME-Version: 1.0 References: <46490518-0cdb-4d11-be9a-374ed5792da8@nvidia.com> In-Reply-To: <46490518-0cdb-4d11-be9a-374ed5792da8@nvidia.com> From: Chenyuan Yang Date: Fri, 26 Jan 2024 13:23:46 -0600 Message-ID: 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: John Hubbard Cc: Matthew Wilcox , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzkaller@googlegroups.com, Zijie Zhao Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: C7C351C0011 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: rxmkxc4589g3tokwpk5ohh93g8wp5716 X-HE-Tag: 1706297038-429478 X-HE-Meta: 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 f8aoOCgZ RjHocWf1Is6eYKZa5LnXjsH9teVkTCsXhdpEoXHrJpSny7QKmsrAAfvAmxE/Sk57kAD4KZaP9pPzSZqC1+EwUnNanCfcx/RxHwNTUbHXi10sTbV5jaremziTSHQ3HQ6fVCu+0n0AhZHimOZd4fM7U21xa1b3vEVIAmxWso7fPDW929QfYzUHf33zDs1tBQpcPTQgA4ABFZ/48L9UysFDAtA6dh/wXfU8+DbIfYyk7BuUc+y02zuephsgHQww0Bw8c1LJffMEM7D/7BLAKXwS82GH3JnknqKF2NhuTSeT0SqGn9fgvTEfs4Ld+4qT53tcIIaXoB2iwRSCY+wCKxQvobFkr6RqAgGaypNcCZGtLP7Fp4etq5joixQk8S62gOvvosIA01SuZRfba5fK03VjdD37jmnvBSPauUVP1EE8IsoBV/9g= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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=E2=80=AFPM John Hubbard = 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 > >