Re: [PATCH 1/1] net/sched: cls_u32: Fix reference counter leak leading to overflow

[Jamal Hadi Salim]

On Wed, May 31, 2023 at 11:03 AM Eric Dumazet <edumazet@xxxxxxxxxx> wrote:
>
> On Wed, May 31, 2023 at 4:16 PM Lee Jones <lee@xxxxxxxxxx> wrote:
> >
> > In the event of a failure in tcf_change_indev(), u32_set_parms() will
> > immediately return without decrementing the recently incremented
> > reference counter.  If this happens enough times, the counter will
> > rollover and the reference freed, leading to a double free which can be
> > used to do 'bad things'.
> >
> > Cc: stable@xxxxxxxxxx # v4.14+
>
> Please add a Fixes: tag.
>
> > Signed-off-by: Lee Jones <lee@xxxxxxxxxx>
> > ---
> >  net/sched/cls_u32.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
> > index 4e2e269f121f8..fad61ca5e90bf 100644
> > --- a/net/sched/cls_u32.c
> > +++ b/net/sched/cls_u32.c
> > @@ -762,8 +762,11 @@ static int u32_set_parms(struct net *net, struct tcf_proto *tp,
> >         if (tb[TCA_U32_INDEV]) {
> >                 int ret;
> >                 ret = tcf_change_indev(net, tb[TCA_U32_INDEV], extack);
>
> This call should probably be done earlier in the function, next to
> tcf_exts_validate_ex()
>
> Otherwise we might ask why the tcf_bind_filter() does not need to be undone.
>
> Something like:
>
> diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
> index 4e2e269f121f8a301368b9783753e055f5af6a4e..ac957ff2216ae18bcabdd3af3b0e127447ef8f91
> 100644
> --- a/net/sched/cls_u32.c
> +++ b/net/sched/cls_u32.c
> @@ -718,13 +718,18 @@ static int u32_set_parms(struct net *net, struct
> tcf_proto *tp,
>                          struct nlattr *est, u32 flags, u32 fl_flags,
>                          struct netlink_ext_ack *extack)
>  {
> -       int err;
> +       int err, ifindex = -1;
>
>         err = tcf_exts_validate_ex(net, tp, tb, est, &n->exts, flags,
>                                    fl_flags, extack);
>         if (err < 0)
>                 return err;
>
> +       if (tb[TCA_U32_INDEV]) {
> +               ifindex = tcf_change_indev(net, tb[TCA_U32_INDEV], extack);
> +               if (ifindex < 0)
> +                       return -EINVAL;
> +       }
>         if (tb[TCA_U32_LINK]) {
>                 u32 handle = nla_get_u32(tb[TCA_U32_LINK]);
>                 struct tc_u_hnode *ht_down = NULL, *ht_old;
> @@ -759,13 +764,9 @@ static int u32_set_parms(struct net *net, struct
> tcf_proto *tp,
>                 tcf_bind_filter(tp, &n->res, base);
>         }
>
> -       if (tb[TCA_U32_INDEV]) {
> -               int ret;
> -               ret = tcf_change_indev(net, tb[TCA_U32_INDEV], extack);
> -               if (ret < 0)
> -                       return -EINVAL;
> -               n->ifindex = ret;
> -       }
> +       if (ifindex >= 0)
> +               n->ifindex = ifindex;
> +

I guess we crossed paths ;->

Please, add a tdc test as well - it doesnt have to be in this patch,
can be a followup.

cheers,
jamal

>         return 0;
>  }