Re: Re: [PATCH] infiniband/core: Fix a use after free in cm_work_handler

[lyl2019]

In the implementation of destory_cm_id(), it restores cm_id_priv by 
"cm_id_priv = container_of(cm_id, struct iwcm_id_private, id);".

And the last line of destory_cm_id() calls "(void)iwcm_deref_id(cm_id_priv);"
to free the cm_id_priv.


> -----原始邮件-----
> 发件人: "Leon Romanovsky" <leon@xxxxxxxxxx>
> 发送时间: 2021-03-11 17:22:03 (星期四)
> 收件人: "Lv Yunlong" <lyl2019@xxxxxxxxxxxxxxxx>
> 抄送: dledford@xxxxxxxxxx, jgg@xxxxxxxx, linux-rdma@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx
> 主题: Re: [PATCH] infiniband/core: Fix a use after free in cm_work_handler
> 
> On Wed, Mar 10, 2021 at 06:21:53PM -0800, Lv Yunlong wrote:
> > In cm_work_handler, it calls destory_cm_id() to release
> > the initial reference of cm_id_priv taken by iw_create_cm_id()
> > and free the cm_id_priv. After destory_cm_id(), iwcm_deref_id
> > (cm_id_priv) will be called and cause a use after free.
> >
> > Fixes: 59c68ac31e15a ("iw_cm: free cm_id resources on the last deref")
> > Signed-off-by: Lv Yunlong <lyl2019@xxxxxxxxxxxxxxxx>
> > ---
> >  drivers/infiniband/core/iwcm.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/infiniband/core/iwcm.c b/drivers/infiniband/core/iwcm.c
> > index da8adadf4755..cb6b4ac45e21 100644
> > --- a/drivers/infiniband/core/iwcm.c
> > +++ b/drivers/infiniband/core/iwcm.c
> > @@ -1035,8 +1035,10 @@ static void cm_work_handler(struct work_struct *_work)
> >
> >  		if (!test_bit(IWCM_F_DROP_EVENTS, &cm_id_priv->flags)) {
> >  			ret = process_event(cm_id_priv, &levent);
> > -			if (ret)
> > +			if (ret) {
> >  				destroy_cm_id(&cm_id_priv->id);
> > +				return;
> 
> The destroy_cm_id() is called to free ->id and not cm_id_priv. This "return"
> leaks cm_id_priv now and what "a use after free" do you see?
> 
> > +			}
> >  		} else
> >  			pr_debug("dropping event %d\n", levent.event);
> >  		if (iwcm_deref_id(cm_id_priv))
> > --
> > 2.25.1
> >
> >