netdev - Re: [PATCH net-next 06/10] cipso_ipv4: use iph_set_totlen in skbuff

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Date:   Sat, 14 Jan 2023 10:38:59 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     network dev <netdev@...r.kernel.org>, davem@...emloft.net,
        kuba@...nel.org, Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        David Ahern <dsahern@...il.com>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Pravin B Shelar <pshelar@....org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Florian Westphal <fw@...len.de>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Ilya Maximets <i.maximets@....org>,
        Aaron Conole <aconole@...hat.com>,
        Roopa Prabhu <roopa@...dia.com>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        Mahesh Bandewar <maheshb@...gle.com>,
        Guillaume Nault <gnault@...hat.com>,
        linux-security-module@...r.kernel.org, selinux@...r.kernel.org
Subject: Re: [PATCH net-next 06/10] cipso_ipv4: use iph_set_totlen in skbuff_setattr

On Fri, Jan 13, 2023 at 10:31 PM Xin Long <lucien.xin@...il.com> wrote:
>
> It may process IPv4 TCP GSO packets in cipso_v4_skbuff_setattr(), so
> the iph->tot_len update should use iph_set_totlen().
>
> Note that for these non GSO packets, the new iph tot_len with extra
> iph option len added may become greater than 65535, the old process
> will cast it and set iph->tot_len to it, which is a bug. In theory,
> iph options shouldn't be added for these big packets in here, a fix
> may be needed here in the future. For now this patch is only to set
> iph->tot_len to 0 when it happens.

I'm not entirely clear on the paragraph above, but we do need to be
able to set/modify the IP options in cipso_v4_skbuff_setattr() in
order to support CIPSO labeling.  I'm open to better and/or
alternative solutions compared to what we are doing now, but I can't
support a change that is a bug waiting to bite us.  My apologies if
I'm interpreting your comments incorrectly and that isn't the case
here.

> Signed-off-by: Xin Long <lucien.xin@...il.com>
> ---
>  net/ipv4/cipso_ipv4.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/ipv4/cipso_ipv4.c b/net/ipv4/cipso_ipv4.c
> index 6cd3b6c559f0..79ae7204e8ed 100644
> --- a/net/ipv4/cipso_ipv4.c
> +++ b/net/ipv4/cipso_ipv4.c
> @@ -2222,7 +2222,7 @@ int cipso_v4_skbuff_setattr(struct sk_buff *skb,
>                 memset((char *)(iph + 1) + buf_len, 0, opt_len - buf_len);
>         if (len_delta != 0) {
>                 iph->ihl = 5 + (opt_len >> 2);
> -               iph->tot_len = htons(skb->len);
> +               iph_set_totlen(iph, skb->len);
>         }
>         ip_send_check(iph);
>
> --
> 2.31.1

--
paul-moore.com