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Message-ID: <20210114103848.5153aa5f@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date: Thu, 14 Jan 2021 10:38:48 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Cong Wang <xiyou.wangcong@...il.com>
Cc: netdev@...r.kernel.org, Cong Wang <cong.wang@...edance.com>,
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 v2] cls_flower: call nla_ok() before nla_next()
On Thu, 14 Jan 2021 08:38:22 -0800 Cong Wang wrote:
> From: Cong Wang <cong.wang@...edance.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@...kaller.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
> }
>
> return 0;
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