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From:   Miklos Szeredi <miklos@szeredi.hu>
Date:   Thu, 1 Jun 2023 14:13:04 +0200
Message-ID: <CAJfpegtHicLw7-KjQem60UPaUyco7h1tZ+4EmOdC-=9=C8Tg8Q@mail.gmail.com>
Subject: Re: [PATCH V1] fuse: Abort the requests under processing queue with a spin_lock
To:     Pradeep Pragallapati <quic_pragalla@quicinc.com>
Cc:     linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
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On Thu, 1 Jun 2023 at 12:02, Pradeep Pragallapati
<quic_pragalla@quicinc.com> wrote:
>
>
> On 5/31/2023 5:22 PM, Miklos Szeredi wrote:
> > On Wed, 31 May 2023 at 11:26, Pradeep P V K <quic_pragalla@quicinc.com> wrote:
> >> There is a potential race/timing issue while aborting the
> >> requests on processing list between fuse_dev_release() and
> >> fuse_abort_conn(). This is resulting into below warnings
> >> and can even result into UAF issues.
> > Okay, but...
> >
> >> [22809.190255][T31644] refcount_t: underflow; use-after-free.
> >> [22809.190266][T31644] WARNING: CPU: 2 PID: 31644 at lib/refcount.c:28
> >> refcount_warn_saturate+0x110/0x158
> >> ...
> >> [22809.190567][T31644] Call trace:
> >> [22809.190567][T31644]  refcount_warn_saturate+0x110/0x158
> >> [22809.190569][T31644]  fuse_file_put+0xfc/0x104
> > ...how can this cause the file refcount to underflow?  That would
> > imply that fuse_request_end() will be called for the same request
> > twice.  I can't see how that can happen with or without the locking
> > change.
> Please ignore this patch. i overlooked it as list_splice in
> fuse_dev_release() and made the change.
> > Do you have a reproducer?
>
> don't have exact/specific steps but i will try to recreate. This is
> observed during stability testing (involves io, reboot, monkey, e.t.c.)
> for 24hrs. So, far this is seen on both 5.15 and 6.1 kernels. Do you
> have any points or speculations to share ?

Do you have KASAN enabled in the kernel?  That might help UAF issues easier.

Thanks,
Miklos