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

From: Jakub Kicinski <[email-masked]>
Date: Fri, 6 May 2022 19:37:34 -0700

On Fri, 6 May 2022 19:10:48 -0700 Eric Dumazet wrote:
> On Fri, May 6, 2022 at 6:54 PM Jakub Kicinski <[email-masked]> 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 :/

> 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
> }