Re: WARNING in wp_page_copy

From: Magnus Karlsson <magnus.karlsson@gmail.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: "Daniel Borkmann" <daniel@iogearbox.net>,
	kirill.shutemov@linux.intel.com, justin.he@arm.com,
	linux-mm@kvack.org,
	syzbot <syzbot+9301f2f33873407d5b33@syzkaller.appspotmail.com>,
	"Andrii Nakryiko" <andriin@fb.com>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Björn Töpel" <bjorn.topel@intel.com>, bpf <bpf@vger.kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	hawk@kernel.org, "Jakub Kicinski" <jakub.kicinski@netronome.com>,
	"John Fastabend" <john.fastabend@gmail.com>,
	"Jonathan Lemon" <jonathan.lemon@gmail.com>,
	"Martin KaFai Lau" <kafai@fb.com>,
	linux-kernel@vger.kernel.org, "Karlsson,
	Magnus" <magnus.karlsson@intel.com>,
	"Network Development" <netdev@vger.kernel.org>,
	"Song Liu" <songliubraving@fb.com>,
	syzkaller-bugs@googlegroups.com, "Yonghong Song" <yhs@fb.com>
Subject: Re: WARNING in wp_page_copy
Date: Wed, 18 Dec 2019 16:00:30 +0100	[thread overview]
Message-ID: <CAJ8uoz358oXf7HGjOdVLO6vXLJqKN8LNV=d1HRQ=ZA=jTtOV2A@mail.gmail.com> (raw)
In-Reply-To: <20191217223808.GA14982@mbp>

On Tue, Dec 17, 2019 at 11:38 PM Catalin Marinas
<catalin.marinas@arm.com> wrote:
>
> On Tue, Dec 17, 2019 at 04:57:34PM +0100, Magnus Karlsson wrote:
> > On Tue, Dec 17, 2019 at 4:40 PM Catalin Marinas <catalin.marinas@arm.com> wrote:
> > > On Tue, Dec 17, 2019 at 02:27:22PM +0100, Magnus Karlsson wrote:
> > > > On Mon, Dec 16, 2019 at 4:10 PM Magnus Karlsson
> > > > <magnus.karlsson@gmail.com> wrote:
> > > > > On Mon, Dec 16, 2019 at 4:00 PM Daniel Borkmann <daniel@iogearbox.net> wrote:
> > > > > > On Sat, Dec 14, 2019 at 08:20:07AM -0800, syzbot wrote:
> > > > > > > syzbot has found a reproducer for the following crash on:
> > > > > > >
> > > > > > > HEAD commit:    1d1997db Revert "nfp: abm: fix memory leak in nfp_abm_u32_..
> > > > > > > git tree:       net-next
> > > > > > > console output: https://syzkaller.appspot.com/x/log.txt?x=1029f851e00000
> > > > > > > kernel config:  https://syzkaller.appspot.com/x/.config?x=cef1fd5032faee91
> > > > > > > dashboard link: https://syzkaller.appspot.com/bug?extid=9301f2f33873407d5b33
> > > > > > > compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> > > > > > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=119d9fb1e00000
> > > > > > >
> > > > > > > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > > > > > > Reported-by: syzbot+9301f2f33873407d5b33@syzkaller.appspotmail.com
> > > > > >
> > > > > > Bjorn / Magnus, given xsk below, PTAL, thanks!
> > > > >
> > > > > Thanks. I will take a look at it right away.
> > > > >
> > > > > /Magnus
> > > >
> > > > After looking through the syzcaller report, I have the following
> > > > hypothesis that would dearly need some comments from MM-savy people
> > > > out there. Syzcaller creates, using mmap, a memory area that is
> > >
> > > I guess that's not an anonymous mmap() since we don't seem to have a
> > > struct page for src in cow_user_page() (the WARN_ON_ONCE path). Do you
> > > have more information on the mmap() call?
> >
> > I have this from the syzcaller logs:
> >
> > mmap(&(0x7f0000001000/0x2000)=nil, 0x2000, 0xfffffe, 0x12, r8, 0x0)
> > getsockopt$XDP_MMAP_OFFSETS(r8, 0x11b, 0x7, &(0x7f0000001300),
> > &(0x7f0000000100)=0x60)
> >
> > The full log can be found at:
> > https://syzkaller.appspot.com/x/repro.syz?x=119d9fb1e00000
>
> Thanks. Prior to mmap, we have:
>
> r8 = socket$xdp(0x2c, 0x3, 0x0)
>
> So basically we have an mmap() on a socket descriptor with a subsequent
> copy_to_user() writing this range. We do we even end up doing CoW on
> such mapping? Maybe the socket code should also implement the .fault()
> file op. It needs more digging.

I am trying to reproduce it with syzkaller, but so far no luck on my
machine. Will keep you posted.

/Magnus

> --
> Catalin