linux-kernel - Re: [syzbot] WARNING in u32

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Date:   Mon, 26 Sep 2022 13:18:25 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     syzbot <syzbot+a2c4601efc75848ba321@...kaller.appspotmail.com>,
        davem@...emloft.net, edumazet@...gle.com, jiri@...nulli.us,
        kuba@...nel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, pabeni@...hat.com,
        syzkaller-bugs@...glegroups.com, xiyou.wangcong@...il.com
Subject: Re: [syzbot] WARNING in u32_change

On Sun, Sep 25, 2022 at 12:14:44PM -0400, Jamal Hadi Salim 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);

Smatch will soon start complaining about these.  Can we instead do:

	sel_size = size_add(struct_size(s, keys, s->nkeys), sizeof(n->sel));

Probably eventually Smatch will be able to detect some times when
struct_size() is used for readability and not for safety so maybe it
won't warn...

regards,
dan carpenter