> -----原始邮件-----
> 发件人: "Christoph Böhmwalder" <christoph.boehmwalder@xxxxxxxxxx>
> 发送时间: 2021-04-01 21:01:20 (星期四)
> 收件人: "Lv Yunlong" <lyl2019@xxxxxxxxxxxxxxxx>
> 抄送: philipp.reisner@xxxxxxxxxx, lars.ellenberg@xxxxxxxxxx, axboe@xxxxxxxxx, linux-block@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, drbd-dev@xxxxxxxxxxxxxxxx
> 主题: Re: [Drbd-dev] [PATCH] drbd: Fix a use after free in get_initial_state
>
> On 4/1/21 1:57 PM, Lv Yunlong wrote:
> > In get_initial_state, it calls notify_initial_state_done(skb,..) if
> > cb->args[5]==1. I see that if genlmsg_put() failed in
> > notify_initial_state_done(), the skb will be freed by nlmsg_free(skb).
> > Then get_initial_state will goto out and the freed skb will be used by
> > return value skb->len.
> >
> > My patch lets skb_len = skb->len and return the skb_len to avoid the uaf.
> >
> > Fixes: a29728463b254 ("drbd: Backport the "events2" command")
> > Signed-off-by: Lv Yunlong <lyl2019@xxxxxxxxxxxxxxxx>
> > ---
> > drivers/block/drbd/drbd_nl.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
> > index bf7de4c7b96c..474f84675d0a 100644
> > --- a/drivers/block/drbd/drbd_nl.c
> > +++ b/drivers/block/drbd/drbd_nl.c
> > @@ -4905,6 +4905,7 @@ static int get_initial_state(struct sk_buff *skb, struct netlink_callback *cb)
> > struct drbd_state_change *state_change = (struct drbd_state_change *)cb->args[0];
> > unsigned int seq = cb->args[2];
> > unsigned int n;
> > + unsigned int skb_len = skb->len;
> > enum drbd_notification_type flags = 0;
> >
> > /* There is no need for taking notification_mutex here: it doesn't
> > @@ -4915,7 +4916,7 @@ static int get_initial_state(struct sk_buff *skb, struct netlink_callback *cb)
> > cb->args[5]--;
> > if (cb->args[5] == 1) {
> > notify_initial_state_done(skb, seq);
> > - goto out;
> > + return skb_len;
> > }
> > n = cb->args[4]++;
> > if (cb->args[4] < cb->args[3])
> >
>
> Thanks for the patch!
>
> I think the problem goes even further: skb can also be freed in the
> notify_*_state_change -> notify_*_state calls below.
>
> Also, at the point where we save skb->len into skb_len, skb is not
> initialized yet. Maybe it makes more sense to not return a length in the
> first place here, but an error code instead.
>
> --
> Christoph Böhmwalder
> LINBIT | Keeping the Digital World Running
> DRBD HA — Disaster Recovery — Software defined Storage
Ok, I see.
I found that drbd_adm_get_initial_state() has called the get_initial_state(),
and return -ENOMEM if it calls remember_old_state() failed.
So, i think that means if get_initial_state() failed on the notify_initial_state_done(),
it should return -ENOMEM too.
I will submit the PATCH v2 to fix the first place. The fixes of the further problem is
hard for me.
Thanks.
