On Thu, Jan 14, 2021 at 10:38 AM Jakub Kicinski <k...@kernel.org> wrote:
>
> On Thu, 14 Jan 2021 08:38:22 -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")
>
> > @@ -1340,9 +1341,6 @@ static int fl_set_enc_opt(struct nlattr **tb, struct
> > fl_flow_key *key,
> > NL_SET_ERR_MSG(extack, "Key and mask miss
> > aligned");
> > return -EINVAL;
> > }
> > -
> > - if (msk_depth)
> > - nla_opt_msk = nla_next(nla_opt_msk,
> > &msk_depth);
> > break;
> > case TCA_FLOWER_KEY_ENC_OPTS_ERSPAN:
> > if (key->enc_opts.dst_opt_type) {
> > @@ -1373,14 +1371,17 @@ static int fl_set_enc_opt(struct nlattr **tb,
> > struct fl_flow_key *key,
> > NL_SET_ERR_MSG(extack, "Key and mask miss
> > aligned");
> > return -EINVAL;
> > }
> > -
> > - 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_ok(nla_opt_msk, msk_depth)) {
> > + NL_SET_ERR_MSG(extack, "Mask attribute is invalid");
> > + return -EINVAL;
> > + }
> > + nla_opt_msk = nla_next(nla_opt_msk, &msk_depth);
>
> we lost the if (msk_depth) now, nla_opt_msk may be NULL -
> neither nla_ok() nor nla_next() take NULL
How is "if (msk_depth)" lost when nla_ok() has a stricter one?
1156 static inline int nla_ok(const struct nlattr *nla, int remaining)
1157 {
1158 return remaining >= (int) sizeof(*nla) &&
1159 nla->nla_len >= sizeof(*nla) &&
1160 nla->nla_len <= remaining;
1161 }
Line 1156 assures msk_depth is not only non-zero but also larger
than the nla struct size, and clearly nla won't be dereferenced unless
this check is passed.
I guess you mean we should not error out for nla_opt_msk==NULL
case as masks are optional?
Thanks.
