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Message-ID: <CAOftzPhBKuxYMM6iEmgWfJ8ikubLh4ORDei9Zpa3=amDRjT_NQ@mail.gmail.com>
Date: Thu, 26 Mar 2020 19:40:03 -0700
From: Joe Stringer <joe@...d.net.nz>
To: Joe Stringer <joe@...d.net.nz>
Cc: Lorenz Bauer <lmb@...udflare.com>, bpf <bpf@...r.kernel.org>,
Networking <netdev@...r.kernel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Alexei Starovoitov <ast@...nel.org>,
Eric Dumazet <eric.dumazet@...il.com>,
Martin Lau <kafai@...com>
Subject: Re: [PATCHv2 bpf-next 1/5] bpf: Add socket assign support
On Thu, Mar 26, 2020 at 3:52 PM Joe Stringer <joe@...d.net.nz> wrote:
>
> On Thu, Mar 26, 2020 at 3:25 AM Lorenz Bauer <lmb@...udflare.com> wrote:
> >
> > On Wed, 25 Mar 2020 at 05:57, Joe Stringer <joe@...d.net.nz> wrote:
> > >
> > > Add support for TPROXY via a new bpf helper, bpf_sk_assign().
> > >
> > > This helper requires the BPF program to discover the socket via a call
> > > to bpf_sk*_lookup_*(), then pass this socket to the new helper. The
> > > helper takes its own reference to the socket in addition to any existing
> > > reference that may or may not currently be obtained for the duration of
> > > BPF processing. For the destination socket to receive the traffic, the
> > > traffic must be routed towards that socket via local route. The
> > > simplest example route is below, but in practice you may want to route
> > > traffic more narrowly (eg by CIDR):
> > >
> > > $ ip route add local default dev lo
> > >
> > > This patch avoids trying to introduce an extra bit into the skb->sk, as
> > > that would require more invasive changes to all code interacting with
> > > the socket to ensure that the bit is handled correctly, such as all
> > > error-handling cases along the path from the helper in BPF through to
> > > the orphan path in the input. Instead, we opt to use the destructor
> > > variable to switch on the prefetch of the socket.
> > >
> > > Signed-off-by: Joe Stringer <joe@...d.net.nz>
> > > ---
> > > v2: Use skb->destructor to determine socket prefetch usage instead of
> > > introducing a new metadata_dst
> > > Restrict socket assign to same netns as TC device
> > > Restrict assigning reuseport sockets
> > > Adjust commit wording
> > > v1: Initial version
> > > ---
> > > include/net/sock.h | 7 +++++++
> > > include/uapi/linux/bpf.h | 25 ++++++++++++++++++++++++-
> > > net/core/filter.c | 31 +++++++++++++++++++++++++++++++
> > > net/core/sock.c | 9 +++++++++
> > > net/ipv4/ip_input.c | 3 ++-
> > > net/ipv6/ip6_input.c | 3 ++-
> > > net/sched/act_bpf.c | 2 ++
> > > tools/include/uapi/linux/bpf.h | 25 ++++++++++++++++++++++++-
> > > 8 files changed, 101 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/include/net/sock.h b/include/net/sock.h
> > > index b5cca7bae69b..2613d21a667a 100644
> > > --- a/include/net/sock.h
> > > +++ b/include/net/sock.h
> > > @@ -1657,6 +1657,7 @@ struct sk_buff *sock_omalloc(struct sock *sk, unsigned long size,
> > > void skb_orphan_partial(struct sk_buff *skb);
> > > void sock_rfree(struct sk_buff *skb);
> > > void sock_efree(struct sk_buff *skb);
> > > +void sock_pfree(struct sk_buff *skb);
> > > #ifdef CONFIG_INET
> > > void sock_edemux(struct sk_buff *skb);
> > > #else
> > > @@ -2526,6 +2527,12 @@ void sock_net_set(struct sock *sk, struct net *net)
> > > write_pnet(&sk->sk_net, net);
> > > }
> > >
> > > +static inline bool
> > > +skb_sk_is_prefetched(struct sk_buff *skb)
> > > +{
> > > + return skb->destructor == sock_pfree;
> > > +}
> > > +
> > > static inline struct sock *skb_steal_sock(struct sk_buff *skb)
> > > {
> > > if (skb->sk) {
> > > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > > index 5d01c5c7e598..0c6f151deebe 100644
> > > --- a/include/uapi/linux/bpf.h
> > > +++ b/include/uapi/linux/bpf.h
> > > @@ -2950,6 +2950,28 @@ union bpf_attr {
> > > * restricted to raw_tracepoint bpf programs.
> > > * Return
> > > * 0 on success, or a negative error in case of failure.
> > > + *
> > > + * int bpf_sk_assign(struct sk_buff *skb, struct bpf_sock *sk, u64 flags)
> > > + * Description
> > > + * Assign the *sk* to the *skb*. When combined with appropriate
> > > + * routing configuration to receive the packet towards the socket,
> > > + * will cause *skb* to be delivered to the specified socket.
> > > + * Subsequent redirection of *skb* via **bpf_redirect**\ (),
> > > + * **bpf_clone_redirect**\ () or other methods outside of BPF may
> > > + * interfere with successful delivery to the socket.
> > > + *
> > > + * This operation is only valid from TC ingress path.
> > > + *
> > > + * The *flags* argument must be zero.
> > > + * Return
> > > + * 0 on success, or a negative errno in case of failure.
> > > + *
> > > + * * **-EINVAL** Unsupported flags specified.
> > > + * * **-ENETUNREACH** Socket is unreachable (wrong netns).
> > > + * * **-ENOENT** Socket is unavailable for assignment.
> > > + * * **-EOPNOTSUPP** Unsupported operation, for example a
> > > + * call from outside of TC ingress.
> > > + * * **-ESOCKTNOSUPPORT** Socket type not supported (reuseport).
> > > */
> > > #define __BPF_FUNC_MAPPER(FN) \
> > > FN(unspec), \
> > > @@ -3073,7 +3095,8 @@ union bpf_attr {
> > > FN(jiffies64), \
> > > FN(read_branch_records), \
> > > FN(get_ns_current_pid_tgid), \
> > > - FN(xdp_output),
> > > + FN(xdp_output), \
> > > + FN(sk_assign),
> > >
> > > /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> > > * function eBPF program intends to call
> > > diff --git a/net/core/filter.c b/net/core/filter.c
> > > index 96350a743539..f7f9b6631f75 100644
> > > --- a/net/core/filter.c
> > > +++ b/net/core/filter.c
> > > @@ -5860,6 +5860,35 @@ static const struct bpf_func_proto bpf_tcp_gen_syncookie_proto = {
> > > .arg5_type = ARG_CONST_SIZE,
> > > };
> > >
> > > +BPF_CALL_3(bpf_sk_assign, struct sk_buff *, skb, struct sock *, sk, u64, flags)
> > > +{
> > > + if (flags != 0)
> > > + return -EINVAL;
> > > + if (!skb_at_tc_ingress(skb))
> > > + return -EOPNOTSUPP;
> > > + if (unlikely(sk->sk_reuseport))
> > > + return -ESOCKTNOSUPPORT;
> > > + if (unlikely(dev_net(skb->dev) != sock_net(sk)))
> > > + return -ENETUNREACH;
> > > + if (unlikely(!refcount_inc_not_zero(&sk->sk_refcnt)))
> > > + return -ENOENT;
> > > +
> > > + skb_orphan(skb);
> > > + skb->sk = sk;
> > > + skb->destructor = sock_pfree;
> > > +
> > > + return 0;
> > > +}
> >
> > Follow up to my email re UDP tests: it seems like the helper doesn't check
> > that the sk is TCP, hence I assumed that you want to add support for
> > both in the same series.
> >
> > Also, is it possible to check that the sk protocol matches skb protocol?
>
> Correction, I was able to get UDP working without the other series (at
> least in Cilium, still working through the tests) so the extra check
> should be unnecessary.
>
> I'll look into options for avoiding crossing packets/sockets of the wrong types.
I looked into these options and found:
* sk->protocol is the L4 proto; skb->protocol is the L3 proto so it
doesn't make sense to compare them
* skb doesn't seem to have any L4 indicator unless you want to start
diving into the packet, which seems not ideal
* I tried using sk->family and ensuring, for example, only AF_INET
sockets can pair with skb->protocol == ETH_P_IP, but I found that in
my integration test I'm using dual-stack sockets so the check was
failing there
* I tried making up some nonsense tests where I cross different types
of sockets on send/recv side and the worst behaviour I could trigger
was timeouts
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