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

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Message-ID: <CADvbK_dvG9LNTTxh9R4QYO_0UHjKTvxaccb2AingaAzyXpzp4g@mail.gmail.com>
Date:   Tue, 12 Jan 2021 19:52:35 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     network dev <netdev@...r.kernel.org>,
        Cong Wang <cong.wang@...edance.com>,
        syzbot+2624e3778b18fc497c92@...kaller.appspotmail.com,
        Pieter Jansen van Vuuren 
        <pieter.jansenvanvuuren@...ronome.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>
Subject: Re: [Patch net] cls_flower: call nla_ok() before nla_next()

On Tue, Jan 12, 2021 at 10:56 AM Cong Wang <xiyou.wangcong@...il.com> 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")
> Cc: Pieter Jansen van Vuuren <pieter.jansenvanvuuren@...ronome.com>
> Cc: Jamal Hadi Salim <jhs@...atatu.com>
> Cc: Xin Long <lucien.xin@...il.com>
> Cc: Jiri Pirko <jiri@...nulli.us>
> Signed-off-by: Cong Wang <cong.wang@...edance.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.

>
>         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);
>                         break;
>                 case TCA_FLOWER_KEY_ENC_OPTS_VXLAN:
> @@ -1341,7 +1343,7 @@ 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);
>                         break;
>                 case TCA_FLOWER_KEY_ENC_OPTS_ERSPAN:
> @@ -1374,7 +1376,7 @@ 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);
>                         break;
>                 default:
> --
> 2.25.1
>