Re: [syzbot] BUG: unable to handle kernel access to user memory in sock_ioctl

From: Dmitry Vyukov <dvyukov@google.com>
To: Ben Dooks <ben.dooks@codethink.co.uk>
Cc: syzbot <syzbot+c23c5421600e9b454849@syzkaller.appspotmail.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	linux-riscv <linux-riscv@lists.infradead.org>,
	andrii@kernel.org, Alexei Starovoitov <ast@kernel.org>,
	bpf <bpf@vger.kernel.org>, Daniel Borkmann <daniel@iogearbox.net>,
	David Miller <davem@davemloft.net>,
	John Fastabend <john.fastabend@gmail.com>,
	Martin KaFai Lau <kafai@fb.com>,
	kpsingh@kernel.org, Jakub Kicinski <kuba@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	netdev <netdev@vger.kernel.org>, Song Liu <songliubraving@fb.com>,
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
	Yonghong Song <yhs@fb.com>
Subject: Re: [syzbot] BUG: unable to handle kernel access to user memory in sock_ioctl
Date: Mon, 15 Mar 2021 12:52:03 +0100	[thread overview]
Message-ID: <CACT4Y+a1pQ96UWEB3pAnbxPZ+6jW2tqSzkTMqJ+XSbZsKLHgAw@mail.gmail.com> (raw)
In-Reply-To: <ed89390a-91e1-320a-fae5-27b7f3a20424@codethink.co.uk>

On Mon, Mar 15, 2021 at 12:30 PM Ben Dooks <ben.dooks@codethink.co.uk> wrote:
>
> On 14/03/2021 11:03, Dmitry Vyukov wrote:
> > On Sun, Mar 14, 2021 at 11:01 AM Dmitry Vyukov <dvyukov@google.com> wrote:
> >>> On Wed, Mar 10, 2021 at 7:28 PM syzbot
> >>> <syzbot+c23c5421600e9b454849@syzkaller.appspotmail.com> wrote:
> >>>>
> >>>> Hello,
> >>>>
> >>>> syzbot found the following issue on:
> >>>>
> >>>> HEAD commit:    0d7588ab riscv: process: Fix no prototype for arch_dup_tas..
> >>>> git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/riscv/linux.git fixes
> >>>> console output: https://syzkaller.appspot.com/x/log.txt?x=122c343ad00000
> >>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=e3c595255fb2d136
> >>>> dashboard link: https://syzkaller.appspot.com/bug?extid=c23c5421600e9b454849
> >>>> userspace arch: riscv64
> >>>>
> >>>> Unfortunately, I don't have any reproducer for this issue yet.
> >>>>
> >>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> >>>> Reported-by: syzbot+c23c5421600e9b454849@syzkaller.appspotmail.com
> >>>
> >>> +riscv maintainers
> >>>
> >>> Another case of put_user crashing.
> >>
> >> There are 58 crashes in sock_ioctl already. Somehow there is a very
> >> significant skew towards crashing with this "user memory without
> >> uaccess routines" in schedule_tail and sock_ioctl of all places in the
> >> kernel that use put_user... This looks very strange... Any ideas
> >> what's special about these 2 locations?
> >
> > I could imagine if such a crash happens after a previous stack
> > overflow and now task data structures are corrupted. But f_getown does
> > not look like a function that consumes way more than other kernel
> > syscalls...
>
> The last crash I looked at suggested somehow put_user got re-entered
> with the user protection turned back on. Either there is a path through
> one of the kernel handlers where this happens or there's something
> weird going on with qemu.

Is there any kind of tracking/reporting that would help to localize
it? I could re-reproduce with that code.

> I'll be trying to get this run up on real hardware this week, the nvme
> with my debian install died last week so I have to go and re-install
> the machine to get development work done on it.
>
> --
> Ben Dooks                               http://www.codethink.co.uk/
> Senior Engineer                         Codethink - Providing Genius
>
> https://www.codethink.co.uk/privacy.html
>
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