Re: [Patch net] cls_flower: call nla_ok() before nla_next()

[Xin Long <lucien.xin@gmail.com>]

On Wed, Jan 13, 2021 at 1:43 AM Cong Wang <xiyou.wangcong@gmail.com> wrote:
>
> On Tue, Jan 12, 2021 at 3:52 AM Xin Long <lucien.xin@gmail.com> wrote:
> >
> > On Tue, Jan 12, 2021 at 10:56 AM Cong Wang <xiyou.wangcong@gmail.com> wrote:
> > >
> > > From: Cong Wang <cong.wang@bytedance.com>
> > >
> > > fl_set_enc_opt() simply checks if there are still bytes left to parse,
> > > but this is not sufficent as syzbot seems to be able to generate
> > > malformatted netlink messages. nla_ok() is more strict so should be
> > > used to validate the next nlattr here.
> > >
> > > And nla_validate_nested_deprecated() has less strict check too, it is
> > > probably too late to switch to the strict version, but we can just
> > > call nla_ok() too after it.
> > >
> > > Reported-and-tested-by: syzbot+2624e3778b18fc497c92@syzkaller.appspotmail.com
> > > Fixes: 0a6e77784f49 ("net/sched: allow flower to match tunnel options")
> > > Fixes: 79b1011cb33d ("net: sched: allow flower to match erspan options")
> > > Cc: Pieter Jansen van Vuuren <pieter.jansenvanvuuren@netronome.com>
> > > Cc: Jamal Hadi Salim <jhs@mojatatu.com>
> > > Cc: Xin Long <lucien.xin@gmail.com>
> > > Cc: Jiri Pirko <jiri@resnulli.us>
> > > Signed-off-by: Cong Wang <cong.wang@bytedance.com>
> > > ---
> > >  net/sched/cls_flower.c | 8 +++++---
> > >  1 file changed, 5 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/net/sched/cls_flower.c b/net/sched/cls_flower.c
> > > index 1319986693fc..e265c443536e 100644
> > > --- a/net/sched/cls_flower.c
> > > +++ b/net/sched/cls_flower.c
> > > @@ -1272,6 +1272,8 @@ static int fl_set_enc_opt(struct nlattr **tb, struct fl_flow_key *key,
> > >
> > >                 nla_opt_msk = nla_data(tb[TCA_FLOWER_KEY_ENC_OPTS_MASK]);
> > >                 msk_depth = nla_len(tb[TCA_FLOWER_KEY_ENC_OPTS_MASK]);
> > > +               if (!nla_ok(nla_opt_msk, msk_depth))
> > > +                       return -EINVAL;
> > >         }
> > I think it's better to also add  NL_SET_ERR_MSG(extack, xxxx);
> > for this error return, like all the other places in this function.
>
> I think ext message is primarily for end users who usually can not
> generate malformat netlink messages.
>
> On the other hand, the nla_validate_nested_deprecated() right above
> the quoted code does not set ext message either.
nla_validate_nested_deprecated(..., extack), it's already done inside
when returns error, no?