Re: [Patch bpf] udp: validate checksum in udp_read_sock()

[John Fastabend <john.fastabend@gmail.com>]

Cong Wang wrote:
> On Mon, Oct 11, 2021 at 10:06 PM John Fastabend
> <john.fastabend@gmail.com> wrote:
> >
> > Cong Wang wrote:
> > > From: Cong Wang <cong.wang@bytedance.com>
> > >
> > > It turns out the skb's in sock receive queue could have
> > > bad checksums, as both ->poll() and ->recvmsg() validate
> > > checksums. We have to do the same for ->read_sock() path
> > > too before they are redirected in sockmap.
> > >
> > > Fixes: d7f571188ecf ("udp: Implement ->read_sock() for sockmap")
> > > Reported-by: Daniel Borkmann <daniel@iogearbox.net>
> > > Reported-by: John Fastabend <john.fastabend@gmail.com>
> > > Cc: Lorenz Bauer <lmb@cloudflare.com>
> > > Cc: Jakub Sitnicki <jakub@cloudflare.com>
> > > Signed-off-by: Cong Wang <cong.wang@bytedance.com>
> > > ---
> > >  net/ipv4/udp.c | 11 +++++++++++
> > >  1 file changed, 11 insertions(+)
> > >
> > > diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> > > index 8536b2a7210b..0ae8ab5e05b4 100644
> > > --- a/net/ipv4/udp.c
> > > +++ b/net/ipv4/udp.c
> > > @@ -1808,6 +1808,17 @@ int udp_read_sock(struct sock *sk, read_descriptor_t *desc,
> > >               skb = skb_recv_udp(sk, 0, 1, &err);
> > >               if (!skb)
> > >                       return err;
> > > +
> > > +             if (udp_lib_checksum_complete(skb)) {
> > > +                     __UDP_INC_STATS(sock_net(sk), UDP_MIB_CSUMERRORS,
> > > +                                     IS_UDPLITE(sk));
> > > +                     __UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS,
> > > +                                     IS_UDPLITE(sk));
> > > +                     atomic_inc(&sk->sk_drops);
> > > +                     kfree_skb(skb);
> >
> > We could use sock_drop() here? Otherwise looks good thanks.
> 
> sock_drop() is in include/linux/skmsg.h, I think we need to move it
> to sock.h before using it here in net/ipv4/udp.c, right?

Yes it would be necessary. Lets not do it here otherwise backports
will be ugly.

Acked-by: John Fastabend <john.fastabend@gmail.com>

> 
> And there are other similar patterns which can be replaced with
> sock_drop(), so we can do the replacement for all in a separate
> patch.
> 
> Thanks.