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

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Message-ID: <1491922048.10587.42.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Tue, 11 Apr 2017 07:47:28 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Alexey Dobriyan <adobriyan@...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 Tue, 2017-04-11 at 12:41 +0300, Alexey Dobriyan wrote:
> 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.

Only shared_info immediately follows skb->head

For other structures, standard debug tools in SLUB/SLB/KASAN already
take care of redzones.