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From:   Zheng Hacker <hackerzheng666@gmail.com>
Date:   Mon, 13 Mar 2023 22:01:21 +0800
Message-ID: <CAJedcCwgvo3meC=k_nPYrRzEj7Hzcy8kqrvHqHLvmPWLjCq_3Q@mail.gmail.com>
Subject: Re: [PATCH net v2] 9p/xen : Fix use after free bug in
 xen_9pfs_front_remove due to race condition
To:     Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Cc:     Zheng Wang <zyytlz.wz@163.com>, ericvh@gmail.com, lucho@ionkov.net,
        asmadeus@codewreck.org, linux_oss@crudebyte.com,
        davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
        pabeni@redhat.com, v9fs-developer@lists.sourceforge.net,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        1395428693sheep@gmail.com, alex000young@gmail.com
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Michal Swiatkowski <michal.swiatkowski@linux.intel.com> =E4=BA=8E2023=E5=B9=
=B43=E6=9C=8813=E6=97=A5=E5=91=A8=E4=B8=80 21:54=E5=86=99=E9=81=93=EF=BC=9A
>
> On Mon, Mar 13, 2023 at 05:00:02PM +0800, Zheng Wang wrote:
> > In xen_9pfs_front_probe, it calls xen_9pfs_front_alloc_dataring
> > to init priv->rings and bound &ring->work with p9_xen_response.
> >
> > When it calls xen_9pfs_front_event_handler to handle IRQ requests,
> > it will finally call schedule_work to start the work.
> >
> > When we call xen_9pfs_front_remove to remove the driver, there
> > may be a sequence as follows:
> >
> > Fix it by finishing the work before cleanup in xen_9pfs_front_free.
> >
> > Note that, this bug is found by static analysis, which might be
> > false positive.
> >
> > CPU0                  CPU1
> >
> >                      |p9_xen_response
> > xen_9pfs_front_remove|
> >   xen_9pfs_front_free|
> > kfree(priv)          |
> > //free priv          |
> >                      |p9_tag_lookup
> >                      |//use priv->client
> >
> > Fixes: 71ebd71921e4 ("xen/9pfs: connect to the backend")
> > Signed-off-by: Zheng Wang <zyytlz.wz@163.com>
> > ---
> > v2:
> > - fix type error of ring found by kernel test robot
> > ---
> >  net/9p/trans_xen.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/net/9p/trans_xen.c b/net/9p/trans_xen.c
> > index c64050e839ac..83764431c066 100644
> > --- a/net/9p/trans_xen.c
> > +++ b/net/9p/trans_xen.c
> > @@ -274,12 +274,17 @@ static const struct xenbus_device_id xen_9pfs_fro=
nt_ids[] =3D {
> >  static void xen_9pfs_front_free(struct xen_9pfs_front_priv *priv)
> >  {
> >       int i, j;
> > +     struct xen_9pfs_dataring *ring =3D NULL;
> Move it before int i, j to have RCT.
>
> >
> >       write_lock(&xen_9pfs_lock);
> >       list_del(&priv->list);
> >       write_unlock(&xen_9pfs_lock);
> >
> >       for (i =3D 0; i < priv->num_rings; i++) {
> > +             /*cancel work*/
> It isn't needed I think, the function cancel_work_sync() tells everything
> here.
>

Get it, will remove it in the next version of patch.

Best regards,
Zheng