netdev - Re: [PATCH v4 net-next 12/12] mlx5: support BIG TCP packets

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Date:   Fri, 6 May 2022 19:43:13 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>,
        netdev <netdev@...r.kernel.org>, Coco Li <lixiaoyan@...gle.com>,
        Tariq Toukan <tariqt@...dia.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Leon Romanovsky <leon@...nel.org>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v4 net-next 12/12] mlx5: support BIG TCP packets

On Fri, May 6, 2022 at 7:37 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Fri, 6 May 2022 19:10:48 -0700 Eric Dumazet wrote:
> > On Fri, May 6, 2022 at 6:54 PM Jakub Kicinski <kuba@...nel.org> wrote:
> > > Without our patches drivers/net/ethernet/mellanox/mlx5/core/ builds
> > > cleanly. Gotta be the new W=1 filed overflow warnings, let's bother
> > > Kees.
> >
> > Note that inline_hdr.start is a 2 byte array.
> >
> > Obviously mlx5 driver copies more than 2 bytes of inlined headers.
> >
> > mlx5e_insert_vlan(eseg->inline_hdr.start, skb, attr->ihs)
> > is called already with attr->ihs > 2
> >
> > So it should already complain ?
>
> It's a static checker, I presume it ignores attr->ihs because
> it can't prove its value is indeed > 2. Unpleasant :/

Well, the unpleasant thing is that I do not see a way to get rid of
this warning.
Networking is full of variable sized headers.

>
> > static inline void mlx5e_insert_vlan(void *start, struct sk_buff *skb, u16 ihs)
> > {
> >    struct vlan_ethhdr *vhdr = (struct vlan_ethhdr *)start;
> >    int cpy1_sz = 2 * ETH_ALEN;
> >    int cpy2_sz = ihs - cpy1_sz;
> >
> >     memcpy(&vhdr->addrs, skb->data, cpy1_sz);
> >     vhdr->h_vlan_proto = skb->vlan_proto;
> >     vhdr->h_vlan_TCI = cpu_to_be16(skb_vlan_tag_get(skb));
> >     memcpy(&vhdr->h_vlan_encapsulated_proto, skb->data + cpy1_sz,
> > cpy2_sz);  // Here, more than 2 bytes are copied already
> > }
>