KASAN poisoning for skb linear data

[Dmitry Vyukov]

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