netdev - Re: [Patch net v3] cls_flower: call nla_ok() before nla

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Date:   Thu, 14 Jan 2021 14:30:00 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Cong Wang <cong.wang@...edance.com>,
        syzbot <syzbot+2624e3778b18fc497c92@...kaller.appspotmail.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Xin Long <lucien.xin@...il.com>, Jiri Pirko <jiri@...nulli.us>
Subject: Re: [Patch net v3] cls_flower: call nla_ok() before nla_next()

On Thu, 14 Jan 2021 13:57:13 -0800 Cong Wang wrote:
> On Thu, Jan 14, 2021 at 1:36 PM Jakub Kicinski <kuba@...nel.org> wrote:
> >
> > On Thu, 14 Jan 2021 13:07:49 -0800 Cong Wang wrote:  
> > > -                     if (msk_depth)
> > > -                             nla_opt_msk = nla_next(nla_opt_msk, &msk_depth);
> > >                       break;
> > >               default:
> > >                       NL_SET_ERR_MSG(extack, "Unknown tunnel option type");
> > >                       return -EINVAL;
> > >               }
> > > +
> > > +             if (!nla_opt_msk)
> > > +                     continue;  
> >
> > Why the switch from !msk_depth to !nla_opt_msk?  
> 
> It is the same, when nla_opt_msk is NULL, msk_depth is 0.
> Checking nla_opt_msk is NULL is more readable to express that
> mask is not provided.
> 
> >
> > Seems like previously providing masks for only subset of options
> > would have worked.  
> 
> I don't think so, every type has this check:
> 
>                         if (key->enc_opts.len != mask->enc_opts.len) {
>                                 NL_SET_ERR_MSG(extack, "Key and mask
> miss aligned");
>                                 return -EINVAL;
>                         }
> 
> which guarantees the numbers are aligned.
> 
> Thanks.

static int fl_set_vxlan_opt(const struct nlattr *nla, struct fl_flow_key *key,
			    int depth, int option_len,
			    struct netlink_ext_ack *extack)
{
	struct nlattr *tb[TCA_FLOWER_KEY_ENC_OPT_VXLAN_MAX + 1];
	struct vxlan_metadata *md;
	int err;

	md = (struct vxlan_metadata *)&key->enc_opts.data[key->enc_opts.len];
	memset(md, 0xff, sizeof(*md));

	if (!depth)
		return sizeof(*md);
		^^^^^^^^^^^^^^^^^^^

The mask is filled with all 1s if attribute is not provided.