linux-kernel - KASAN poisoning for skb linear data

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Date:   Mon, 15 Jan 2018 15:15:04 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     David Miller <davem@...emloft.net>,
        Willem de Bruijn <willemb@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        andreyknvl <andreyknvl@...gle.com>
Subject: KASAN poisoning for skb linear data

Hi,

As far as I understand pskb_may_pull() plays important role in packet
parsing for all protocols. And we did custom fragmentation of packets
emitted via tun (IFF_NAPI_FRAGS). However, it seems that it does not
give any results (bugs found), and I think the reason for this is that
linear data is rounded up and is usually quite large. So if a parsing
function does pskb_may_pull(1), or does not do it at all, it can
usually access more and it will go unnoticed. KASAN has an ability to
do custom poisoning: it can poison/unpoison any memory range, and then
detect any reads/writes to that range. What do you think about adding
custom KASAN poisoning to pskb_may_pull() and switching it to
non-eager mode (pull only what was requested) under KASAN? Do you
think it has potential for finding important bugs? What amount of work
is this?

Thanks