On Thu, Jul 02, 2020 at 11:24 AM CEST, Jakub Sitnicki 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 <ma...@cloudflare.com>
> Signed-off-by: Jakub Sitnicki <ja...@cloudflare.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/net/core/filter.c b/net/core/filter.c
> index c796e141ea8e..286f90e0c824 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -9219,6 +9219,192 @@ const struct bpf_verifier_ops
> sk_reuseport_verifier_ops = {
>
> const struct bpf_prog_ops sk_reuseport_prog_ops = {
> };
> +
> +BPF_CALL_3(bpf_sk_lookup_assign, struct bpf_sk_lookup_kern *, ctx,
> + struct sock *, sk, u64, flags)
> +{
> + if (unlikely(flags & ~(BPF_SK_LOOKUP_F_REPLACE |
> + BPF_SK_LOOKUP_F_NO_REUSEPORT)))
> + return -EINVAL;
> + if (unlikely(sk_is_refcounted(sk)))
> + return -ESOCKTNOSUPPORT; /* reject non-RCU freed sockets */
> + if (unlikely(sk->sk_state == TCP_ESTABLISHED))
> + return -ESOCKTNOSUPPORT; /* reject connected sockets */
> +
> + /* Check if socket is suitable for packet L3/L4 protocol */
> + if (sk->sk_protocol != ctx->protocol)
> + return -EPROTOTYPE;
> + if (sk->sk_family != ctx->family &&
> + (sk->sk_family == AF_INET || ipv6_only_sock(sk)))
> + return -EAFNOSUPPORT;
> +
> + if (ctx->selected_sk && !(flags & BPF_SK_LOOKUP_F_REPLACE))
> + return -EEXIST;
> +
> + /* Select socket as lookup result */
> + ctx->selected_sk = sk;
> + ctx->no_reuseport = flags & BPF_SK_LOOKUP_F_NO_REUSEPORT;
> + return 0;
> +}
> +
> +static const struct bpf_func_proto bpf_sk_lookup_assign_proto = {
> + .func = bpf_sk_lookup_assign,
> + .gpl_only = false,
> + .ret_type = RET_INTEGER,
> + .arg1_type = ARG_PTR_TO_CTX,
> + .arg2_type = ARG_PTR_TO_SOCKET,
> + .arg3_type = ARG_ANYTHING,
> +};
> +
> +static const struct bpf_func_proto *
> +sk_lookup_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> +{
> + switch (func_id) {
> + case BPF_FUNC_sk_assign:
> + return &bpf_sk_lookup_assign_proto;
> + case BPF_FUNC_sk_release:
> + return &bpf_sk_release_proto;
> + default:
> + return bpf_base_func_proto(func_id);
> + }
> +}
> +
> +static bool sk_lookup_is_valid_access(int off, int size,
> + enum bpf_access_type type,
> + const struct bpf_prog *prog,
> + struct bpf_insn_access_aux *info)
> +{
> + if (off < 0 || off >= sizeof(struct bpf_sk_lookup))
> + return false;
> + if (off % size != 0)
> + return false;
> + if (type != BPF_READ)
> + return false;
> +
> + switch (off) {
> + case bpf_ctx_range(struct bpf_sk_lookup, family):
> + case bpf_ctx_range(struct bpf_sk_lookup, protocol):
> + case bpf_ctx_range(struct bpf_sk_lookup, remote_ip4):
> + case bpf_ctx_range(struct bpf_sk_lookup, local_ip4):
> + case bpf_ctx_range_till(struct bpf_sk_lookup, remote_ip6[0],
> remote_ip6[3]):
> + case bpf_ctx_range_till(struct bpf_sk_lookup, local_ip6[0],
> local_ip6[3]):
> + case bpf_ctx_range(struct bpf_sk_lookup, remote_port):
> + case bpf_ctx_range(struct bpf_sk_lookup, local_port):
> + return size == sizeof(__u32);
> +
> + case offsetof(struct bpf_sk_lookup, sk):
> + info->reg_type = PTR_TO_SOCKET;
There's a bug here. bpf_sk_lookup 'sk' field is initially NULL.
reg_type should be PTR_TO_SOCKET_OR_NULL to inform the verifier.
Will fix in v4.
> + return size == sizeof(__u64);
> +
> + default:
> + return false;
> + }
> +}
> +
> +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)
> +{
> + struct bpf_insn *insn = insn_buf;
> +#if IS_ENABLED(CONFIG_IPV6)
> + int off;
> +#endif
> +
> + switch (si->off) {
> + case offsetof(struct bpf_sk_lookup, family):
> + BUILD_BUG_ON(sizeof_field(struct bpf_sk_lookup_kern, family) !=
> 2);
> +
> + *insn++ = BPF_LDX_MEM(BPF_H, si->dst_reg, si->src_reg,
> + offsetof(struct bpf_sk_lookup_kern,
> family));
> + break;
> +
> + case offsetof(struct bpf_sk_lookup, protocol):
> + BUILD_BUG_ON(sizeof_field(struct bpf_sk_lookup_kern, protocol)
> != 2);
> +
> + *insn++ = BPF_LDX_MEM(BPF_H, si->dst_reg, si->src_reg,
> + offsetof(struct bpf_sk_lookup_kern,
> protocol));
> + break;
> +
> + case offsetof(struct bpf_sk_lookup, remote_ip4):
> + BUILD_BUG_ON(sizeof_field(struct bpf_sk_lookup_kern, v4.saddr)
> != 4);
> +
> + *insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->src_reg,
> + offsetof(struct bpf_sk_lookup_kern,
> v4.saddr));
> + break;
> +
> + case offsetof(struct bpf_sk_lookup, local_ip4):
> + BUILD_BUG_ON(sizeof_field(struct bpf_sk_lookup_kern, v4.daddr)
> != 4);
> +
> + *insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->src_reg,
> + offsetof(struct bpf_sk_lookup_kern,
> v4.daddr));
> + break;
> +
> + case bpf_ctx_range_till(struct bpf_sk_lookup,
> + remote_ip6[0], remote_ip6[3]):
> +#if IS_ENABLED(CONFIG_IPV6)
> + BUILD_BUG_ON(sizeof_field(struct in6_addr, s6_addr32[0]) != 4);
> +
> + off = si->off;
> + off -= offsetof(struct bpf_sk_lookup, remote_ip6[0]);
> + off += offsetof(struct in6_addr, s6_addr32[0]);
> + *insn++ = BPF_LDX_MEM(BPF_SIZEOF(void *), si->dst_reg,
> si->src_reg,
> + offsetof(struct bpf_sk_lookup_kern,
> v6.saddr));
> + *insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->dst_reg, off);
> +#else
> + *insn++ = BPF_MOV32_IMM(si->dst_reg, 0);
> +#endif
> + break;
> +
> + case bpf_ctx_range_till(struct bpf_sk_lookup,
> + local_ip6[0], local_ip6[3]):
> +#if IS_ENABLED(CONFIG_IPV6)
> + BUILD_BUG_ON(sizeof_field(struct in6_addr, s6_addr32[0]) != 4);
> +
> + off = si->off;
> + off -= offsetof(struct bpf_sk_lookup, local_ip6[0]);
> + off += offsetof(struct in6_addr, s6_addr32[0]);
> + *insn++ = BPF_LDX_MEM(BPF_SIZEOF(void *), si->dst_reg,
> si->src_reg,
> + offsetof(struct bpf_sk_lookup_kern,
> v6.daddr));
> + *insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->dst_reg, off);
> +#else
> + *insn++ = BPF_MOV32_IMM(si->dst_reg, 0);
> +#endif
> + break;
> +
> + case offsetof(struct bpf_sk_lookup, remote_port):
> + BUILD_BUG_ON(sizeof_field(struct bpf_sk_lookup_kern, sport) !=
> 2);
> +
> + *insn++ = BPF_LDX_MEM(BPF_H, si->dst_reg, si->src_reg,
> + offsetof(struct bpf_sk_lookup_kern,
> sport));
> + break;
> +
> + case offsetof(struct bpf_sk_lookup, local_port):
> + BUILD_BUG_ON(sizeof_field(struct bpf_sk_lookup_kern, dport) !=
> 2);
> +
> + *insn++ = BPF_LDX_MEM(BPF_H, si->dst_reg, si->src_reg,
> + offsetof(struct bpf_sk_lookup_kern,
> dport));
> + break;
> +
> + case offsetof(struct bpf_sk_lookup, sk):
> + *insn++ = BPF_LDX_MEM(BPF_SIZEOF(void *), si->dst_reg,
> si->src_reg,
> + offsetof(struct bpf_sk_lookup_kern,
> selected_sk));
> + break;
> + }
> +
> + return insn - insn_buf;
> +}
> +
> +const struct bpf_prog_ops sk_lookup_prog_ops = {
> +};
> +
> +const struct bpf_verifier_ops sk_lookup_verifier_ops = {
> + .get_func_proto = sk_lookup_func_proto,
> + .is_valid_access = sk_lookup_is_valid_access,
> + .convert_ctx_access = sk_lookup_convert_ctx_access,
> +};
> +
> #endif /* CONFIG_INET */
>
> DEFINE_BPF_DISPATCHER(xdp)
[...]
