linux-kernel - Re: [syzbot] INFO: task hung in fuse_simple

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Date:   Fri, 6 Aug 2021 13:09:47 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Miklos Szeredi <miklos@...redi.hu>
Cc:     syzbot <syzkaller@...glegroups.com>,
        syzbot <syzbot+46fe899420456e014d6b@...kaller.appspotmail.com>,
        areeba.ahmed@...uregulfpak.com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: [syzbot] INFO: task hung in fuse_simple_request

On Fri, 6 Aug 2021 at 11:34, Miklos Szeredi <miklos@...redi.hu> wrote:
> > > Hi,
> > >
> > > I'm not sure what to make of this report.
> > >
> > > Does syzbot try to kill all tasks before generating such a hung task report?
> > >
> > > Does it use the fuse specific /sys/fs/fuse/connections/*/abort to
> > > terminate stuck filesystems?
> >
> > Hi Miklos,
> >
> > Grepping the C reproducer for "/sys/fs/fuse/connections", it seems
> > that it tries to abort all connections.
>
> Hi  Dmitry,
>
> So this could indicate a bug in the abort code of fuse, or it could
> indicate that the test case DoS-es the system so that the abort code
> simply doesn't get the resources to execute.
>
> Can the two be differentiated somehow?

I think we need to take a closer look at what happens here. I've filed
https://github.com/google/syzkaller/issues/498#issuecomment-894185550
for this.
The overall idea is that DoS should not be possible by construction
with various sandboxing so that the system does not report what is not
a bug at all. But it's not always easy to achieve.