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Message-ID: <CAEf4BzZ7-0TFD4+NqpK9X=Yuiem89Ug27v90fev=nn+3anCTpA@mail.gmail.com>
Date: Wed, 8 Jul 2020 21:08:56 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Jakub Sitnicki <jakub@...udflare.com>
Cc: bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
kernel-team <kernel-team@...udflare.com>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
"David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
Marek Majkowski <marek@...udflare.com>
Subject: Re: [PATCH bpf-next v3 02/16] bpf: Introduce SK_LOOKUP program type
with a dedicated attach point
On Thu, Jul 2, 2020 at 2:25 AM Jakub Sitnicki <jakub@...udflare.com> wrote:
>
> Add a new program type BPF_PROG_TYPE_SK_LOOKUP with a dedicated attach type
> BPF_SK_LOOKUP. The new program kind is to be invoked by the transport layer
> when looking up a listening socket for a new connection request for
> connection oriented protocols, or when looking up an unconnected socket for
> a packet for connection-less protocols.
>
> When called, SK_LOOKUP BPF program can select a socket that will receive
> the packet. This serves as a mechanism to overcome the limits of what
> bind() API allows to express. Two use-cases driving this work are:
>
> (1) steer packets destined to an IP range, on fixed port to a socket
>
> 192.0.2.0/24, port 80 -> NGINX socket
>
> (2) steer packets destined to an IP address, on any port to a socket
>
> 198.51.100.1, any port -> L7 proxy socket
>
> In its run-time context program receives information about the packet that
> triggered the socket lookup. Namely IP version, L4 protocol identifier, and
> address 4-tuple. Context can be further extended to include ingress
> interface identifier.
>
> To select a socket BPF program fetches it from a map holding socket
> references, like SOCKMAP or SOCKHASH, and calls bpf_sk_assign(ctx, sk, ...)
> helper to record the selection. Transport layer then uses the selected
> socket as a result of socket lookup.
>
> This patch only enables the user to attach an SK_LOOKUP program to a
> network namespace. Subsequent patches hook it up to run on local delivery
> path in ipv4 and ipv6 stacks.
>
> Suggested-by: Marek Majkowski <marek@...udflare.com>
> Signed-off-by: Jakub Sitnicki <jakub@...udflare.com>
> ---
>
> Notes:
> v3:
> - Allow bpf_sk_assign helper to replace previously selected socket only
> when BPF_SK_LOOKUP_F_REPLACE flag is set, as a precaution for multiple
> programs running in series to accidentally override each other's verdict.
> - Let BPF program decide that load-balancing within a reuseport socket group
> should be skipped for the socket selected with bpf_sk_assign() by passing
> BPF_SK_LOOKUP_F_NO_REUSEPORT flag. (Martin)
> - Extend struct bpf_sk_lookup program context with an 'sk' field containing
> the selected socket with an intention for multiple attached program
> running in series to see each other's choices. However, currently the
> verifier doesn't allow checking if pointer is set.
> - Use bpf-netns infra for link-based multi-program attachment. (Alexei)
> - Get rid of macros in convert_ctx_access to make it easier to read.
> - Disallow 1-,2-byte access to context fields containing IP addresses.
>
> v2:
> - Make bpf_sk_assign reject sockets that don't use RCU freeing.
> Update bpf_sk_assign docs accordingly. (Martin)
> - Change bpf_sk_assign proto to take PTR_TO_SOCKET as argument. (Martin)
> - Fix broken build when CONFIG_INET is not selected. (Martin)
> - Rename bpf_sk_lookup{} src_/dst_* fields remote_/local_*. (Martin)
> - Enforce BPF_SK_LOOKUP attach point on load & attach. (Martin)
>
> include/linux/bpf-netns.h | 3 +
> include/linux/bpf_types.h | 2 +
> include/linux/filter.h | 19 ++++
> include/uapi/linux/bpf.h | 74 +++++++++++++++
> kernel/bpf/net_namespace.c | 5 +
> kernel/bpf/syscall.c | 9 ++
> net/core/filter.c | 186 +++++++++++++++++++++++++++++++++++++
> scripts/bpf_helpers_doc.py | 9 +-
> 8 files changed, 306 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/bpf-netns.h b/include/linux/bpf-netns.h
> index 4052d649f36d..cb1d849c5d4f 100644
> --- a/include/linux/bpf-netns.h
> +++ b/include/linux/bpf-netns.h
> @@ -8,6 +8,7 @@
> enum netns_bpf_attach_type {
> NETNS_BPF_INVALID = -1,
> NETNS_BPF_FLOW_DISSECTOR = 0,
> + NETNS_BPF_SK_LOOKUP,
> MAX_NETNS_BPF_ATTACH_TYPE
> };
>
[...]
> +struct bpf_sk_lookup_kern {
> + u16 family;
> + u16 protocol;
> + union {
> + struct {
> + __be32 saddr;
> + __be32 daddr;
> + } v4;
> + struct {
> + const struct in6_addr *saddr;
> + const struct in6_addr *daddr;
> + } v6;
> + };
> + __be16 sport;
> + u16 dport;
> + struct sock *selected_sk;
> + bool no_reuseport;
> +};
> +
> #endif /* __LINUX_FILTER_H__ */
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 0cb8ec948816..8dd6e6ce5de9 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -189,6 +189,7 @@ enum bpf_prog_type {
> BPF_PROG_TYPE_STRUCT_OPS,
> BPF_PROG_TYPE_EXT,
> BPF_PROG_TYPE_LSM,
> + BPF_PROG_TYPE_SK_LOOKUP,
> };
>
> enum bpf_attach_type {
> @@ -226,6 +227,7 @@ enum bpf_attach_type {
> BPF_CGROUP_INET4_GETSOCKNAME,
> BPF_CGROUP_INET6_GETSOCKNAME,
> BPF_XDP_DEVMAP,
> + BPF_SK_LOOKUP,
Point not specific to your changes, but I wanted to bring it up for a
while now, so thought this one might be as good an opportunity as any.
It seems like enum bpf_attach_type originally was intended for only
cgroup BPF programs. To that end, cgroup_bpf has a bunch of fields
with sizes proportional to MAX_BPF_ATTACH_TYPE. It costs at least
8+4+16=28 bytes for each different type *per each cgroup*. At this
point, we have 22 cgroup-specific attach types, and this will be the
13th non-cgroup attach type. So cgroups pay a price for each time we
extend bpf_attach_type with a new non-cgroup attach type. cgroup_bpf
is now 336 bytes bigger than it needs to be.
So I wanted to propose that we do the same thing for cgroup_bpf as you
did for net_ns with netns_bpf_attach_type: have a densely-packed enum
just for cgroup attach types and translate now generic bpf_attach_type
to cgroup-specific cgroup_bpf_attach_type.
I wonder what people think? Is that a good idea? Is anyone up for doing this?
> __MAX_BPF_ATTACH_TYPE
> };
>
[...]
> +
> +static u32 sk_lookup_convert_ctx_access(enum bpf_access_type type,
> + const struct bpf_insn *si,
> + struct bpf_insn *insn_buf,
> + struct bpf_prog *prog,
> + u32 *target_size)
Would it be too extreme to rely on BTF and direct memory access
(similar to tp_raw, fentry/fexit, etc) for accessing context fields,
instead of all this assembly rewrites? So instead of having
bpf_sk_lookup and bpf_sk_lookup_kern, it will always be a full variant
(bpf_sk_lookup_kern, or however we'd want to name it then) and
verifier will just ensure that direct memory reads go to the right
field boundaries?
> +{
> + struct bpf_insn *insn = insn_buf;
> +#if IS_ENABLED(CONFIG_IPV6)
> + int off;
> +#endif
> +
[...]
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