linux-kernel - Re: [PATCH net-next v4 3/5] net: hdlc_fr: Improve the initial checks when we receive an skb

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Date:   Fri, 30 Oct 2020 12:30:49 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Xie He <xie.he.0141@...il.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Krzysztof Halasa <khc@...waw.pl>
Subject: Re: [PATCH net-next v4 3/5] net: hdlc_fr: Improve the initial checks
 when we receive an skb

On Thu, Oct 29, 2020 at 10:33 PM Xie He <xie.he.0141@...il.com> wrote:
>
> 1.
> Change the skb->len check from "<= 4" to "< 4".
> At first we only need to ensure a 4-byte header is present. We indeed
> normally need the 5th byte, too, but it'd be more logical and cleaner
> to check its existence when we actually need it.
>
> 2.
> Add an fh->ea2 check to the initial checks in fr_rx. fh->ea2 == 1 means
> the second address byte is the final address byte. We only support the
> case where the address length is 2 bytes.

Can you elaborate a bit for readers not intimately familiar with the codebase?

Is there something in the following code that has this implicit
assumption on 2-byte address lengths?