On Tue, Jan 12, 2021 at 5:38 PM Jakub Kicinski <k...@kernel.org> wrote:
>
> On Mon, 11 Jan 2021 18:55:48 -0800 Cong Wang wrote:
> > From: Cong Wang <cong.w...@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+2624e3778b18fc497...@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.jansenvanvuu...@netronome.com>
> > Cc: Jamal Hadi Salim <j...@mojatatu.com>
> > Cc: Xin Long <lucien....@gmail.com>
> > Cc: Jiri Pirko <j...@resnulli.us>
> > Signed-off-by: Cong Wang <cong.w...@bytedance.com>
>
> Thanks for keeping up with the syzbot bugs!
>
> > 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;
>
> Can we just add another call to nla_validate_nested_deprecated()
> here instead of having to worry about each attr individually?
No, we can not parse the nested attr here because different key types
have different attributes.
> See below..
>
> > }
> >
> > nla_for_each_attr(nla_opt_key, nla_enc_key,
> > @@ -1308,7 +1310,7 @@ static int fl_set_enc_opt(struct nlattr **tb, struct
> > fl_flow_key *key,
> > return -EINVAL;
> > }
> >
> > - if (msk_depth)
> > + if (nla_ok(nla_opt_msk, msk_depth))
> > nla_opt_msk = nla_next(nla_opt_msk,
> > &msk_depth);
>
> Should we not error otherwise? if msk_depth && !nla_ok() then the
> message is clearly misformatted. If we don't error out we'll keep
> reusing the same mask over and over, while the intention of this
> code was to have mask per key AFAICT.
Yeah, erroring out sounds better. Will change this in v2.
Thanks!
