netdev - Re: [PATCH] net: move padding in struct skb_shared

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Message-ID: <CACVxJT9ixBPtO4JN=dgLT_gbDOQ8tL_kTFfoYmDahaomatCKEw@mail.gmail.com>
Date:   Tue, 11 Apr 2017 12:41:08 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Eric Dumazet <edumazet@...gle.com>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: move padding in struct skb_shared_info

On Mon, Apr 10, 2017 at 5:43 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Mon, 2017-04-10 at 11:07 +0300, Alexey Dobriyan wrote:
>>  struct skb_shared_info {
>> -     unsigned short  _unused;
>>       unsigned char   nr_frags;
>>       __u8            tx_flags;
>>       unsigned short  gso_size;
>
> Nack
>
> This exact placement was discussed at Netconf and Netdev.
>
> We had off-by-one errors in the past leading to nr_frags being mangled,
> and some exploits were quite happy to use these bugs.
>
> Some shuffling in shared_info might help us to find other bugs, and give
> more work to security researchers

By this logic there should be redzone around every field in networking stack.