linux-kernel - Re: [syzbot] BUG: unable to handle kernel access to user memory in sock

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Message-ID: <CACT4Y+a1pQ96UWEB3pAnbxPZ+6jW2tqSzkTMqJ+XSbZsKLHgAw@mail.gmail.com>
Date:   Mon, 15 Mar 2021 12:52:03 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Ben Dooks <ben.dooks@...ethink.co.uk>
Cc:     syzbot <syzbot+c23c5421600e9b454849@...kaller.appspotmail.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-riscv <linux-riscv@...ts.infradead.org>, andrii@...nel.org,
        Alexei Starovoitov <ast@...nel.org>, bpf <bpf@...r.kernel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        David Miller <davem@...emloft.net>,
        John Fastabend <john.fastabend@...il.com>,
        Martin KaFai Lau <kafai@...com>, kpsingh@...nel.org,
        Jakub Kicinski <kuba@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        Song Liu <songliubraving@...com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Yonghong Song <yhs@...com>
Subject: Re: [syzbot] BUG: unable to handle kernel access to user memory in sock_ioctl

On Mon, Mar 15, 2021 at 12:30 PM Ben Dooks <ben.dooks@...ethink.co.uk> wrote:
>
> On 14/03/2021 11:03, Dmitry Vyukov wrote:
> > On Sun, Mar 14, 2021 at 11:01 AM Dmitry Vyukov <dvyukov@...gle.com> wrote:
> >>> On Wed, Mar 10, 2021 at 7:28 PM syzbot
> >>> <syzbot+c23c5421600e9b454849@...kaller.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@...kaller.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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