Re: [PATCH net v2] 9p/xen : Fix use after free bug in xen_9pfs_front_remove due to race condition

[Zheng Hacker]

Michal Swiatkowski <michal.swiatkowski@xxxxxxxxxxxxxxx> 于2023年3月13日周一 22:08写道：
>
> On Mon, Mar 13, 2023 at 10:01:21PM +0800, Zheng Hacker wrote:
> > Michal Swiatkowski <michal.swiatkowski@xxxxxxxxxxxxxxx> 于2023年3月13日周一 21:54写道：
> > >
> > > 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@xxxxxxx>
> > > > ---
> > > > 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_front_ids[] = {
> > > >  static void xen_9pfs_front_free(struct xen_9pfs_front_priv *priv)
> > > >  {
> > > >       int i, j;
> > > > +     struct xen_9pfs_dataring *ring = NULL;
> > > Move it before int i, j to have RCT.
> > >
> Sorry I didn't notice it before, move the definition to for loop.
>

Get it, will correct it in the next patch. Thanks for your notice :)

> > > >
> > > >       write_lock(&xen_9pfs_lock);
> > > >       list_del(&priv->list);
> > > >       write_unlock(&xen_9pfs_lock);
> > > >
> > > >       for (i = 0; i < priv->num_rings; i++) {
> Here:
> struct xen_9pfs_dataring *ring = &priv->rings[i];
>

Best regards,
Zheng