netdev - Re: [syzbot] WARNING in u32

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Message-ID: <CANn89i+4pgJe8M1cjLF6SkqG1Yp6e+5J2xEkMdSChiVYKMC09g@mail.gmail.com>
Date:   Sun, 25 Sep 2022 09:28:53 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     syzbot <syzbot+a2c4601efc75848ba321@...kaller.appspotmail.com>,
        David Miller <davem@...emloft.net>,
        Jiri Pirko <jiri@...nulli.us>,
        Jakub Kicinski <kuba@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>, Paolo Abeni <pabeni@...hat.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [syzbot] WARNING in u32_change

On Sun, Sep 25, 2022 at 9:14 AM Jamal Hadi Salim <jhs@...atatu.com> wrote:
>
> On Sun, Sep 25, 2022 at 11:38 AM Jamal Hadi Salim <jhs@...atatu.com> wrote:
> >
> > Is there a way to tell the boat "looking into it?"
>
>
> I guess I have to swim across to it to get the message;->
>
> I couldnt see the warning message  but it is obvious by inspection that
> the memcpy is broken. We should add more test coverage.
> This should fix it. Will send a formal patch later:
>
> diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
> index 4d27300c2..591cbbf27 100644
> --- a/net/sched/cls_u32.c
> +++ b/net/sched/cls_u32.c
> @@ -1019,7 +1019,7 @@ static int u32_change(struct net *net, struct
> sk_buff *in_skb,
>         }
>
>         s = nla_data(tb[TCA_U32_SEL]);
> -       sel_size = struct_size(s, keys, s->nkeys);
> +       sel_size = struct_size(s, keys, s->nkeys) + sizeof(n->sel);
>         if (nla_len(tb[TCA_U32_SEL]) < sel_size) {
>                 err = -EINVAL;
>                 goto erridr;

This patch is not needed, please look at struct_size() definition.

Here, we might switch to unsafe_memcpy() instead of memcpy()