Re: [Qemu-devel] [PATCH 11/14] mirror: Fix potential use-after-free in active commit

[Kevin Wolf]

Am 11.09.2018 um 10:31 hat Fam Zheng geschrieben:
> On Fri, 09/07 18:15, Kevin Wolf wrote:
> > When starting an active commit job, other callbacks can run before
> > mirror_start_job() calls bdrv_ref() where needed and cause the nodes to
> > go away. Add another pair of bdrv_ref/unref() around it to protect
> > against this case.
> > 
> > Signed-off-by: Kevin Wolf <address@hidden>
> > ---
> >  block/mirror.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> > 
> > diff --git a/block/mirror.c b/block/mirror.c
> > index 6cc10df5c9..c42999eadf 100644
> > --- a/block/mirror.c
> > +++ b/block/mirror.c
> > @@ -1679,6 +1679,11 @@ void commit_active_start(const char *job_id, 
> > BlockDriverState *bs,
> >  
> >      orig_base_flags = bdrv_get_flags(base);
> >  
> > +    /* bdrv_reopen() drains, which might make the BDSes go away before a
> > +     * reference is taken in mirror_start_job(). */
> > +    bdrv_ref(bs);
> > +    bdrv_ref(base);
> > +
> >      if (bdrv_reopen(base, bs->open_flags, errp)) {
> 
> Doesn't it need bdrv_unref's in this branch?

Yes, of course. Thanks for catching this!

Kevin