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* [PATCH bpf-next v2 1/5] bpf: expose is_mptcp flag to bpf_tcp_sock
@ 2020-09-11 14:30 Nicolas Rybowski
  2020-09-11 14:30 ` [PATCH bpf-next v2 2/5] mptcp: attach subflow socket to parent cgroup Nicolas Rybowski
                   ` (5 more replies)
  0 siblings, 6 replies; 14+ messages in thread
From: Nicolas Rybowski @ 2020-09-11 14:30 UTC (permalink / raw)
  To: Alexei Starovoitov, Daniel Borkmann, Martin KaFai Lau, Song Liu,
	Yonghong Song, Andrii Nakryiko, John Fastabend, KP Singh,
	David S. Miller, Jakub Kicinski
  Cc: Nicolas Rybowski, Matthieu Baerts, Mat Martineau, netdev, bpf,
	linux-kernel

is_mptcp is a field from struct tcp_sock used to indicate that the
current tcp_sock is part of the MPTCP protocol.

In this protocol, a first socket (mptcp_sock) is created with
sk_protocol set to IPPROTO_MPTCP (=262) for control purpose but it
isn't directly on the wire. This is the role of the subflow (kernel)
sockets which are classical tcp_sock with sk_protocol set to
IPPROTO_TCP. The only way to differentiate such sockets from plain TCP
sockets is the is_mptcp field from tcp_sock.

Such an exposure in BPF is thus required to be able to differentiate
plain TCP sockets from MPTCP subflow sockets in BPF_PROG_TYPE_SOCK_OPS
programs.

The choice has been made to silently pass the case when CONFIG_MPTCP is
unset by defaulting is_mptcp to 0 in order to make BPF independent of
the MPTCP configuration. Another solution is to make the verifier fail
in 'bpf_tcp_sock_is_valid_ctx_access' but this will add an additional
'#ifdef CONFIG_MPTCP' in the BPF code and a same injected BPF program
will not run if MPTCP is not set.

An example use-case is provided in
https://github.com/multipath-tcp/mptcp_net-next/tree/scripts/bpf/examples

Suggested-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Acked-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Acked-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Nicolas Rybowski <nicolas.rybowski@tessares.net>
---
 include/uapi/linux/bpf.h       | 1 +
 net/core/filter.c              | 9 ++++++++-
 tools/include/uapi/linux/bpf.h | 1 +
 3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 7dd314176df7..7d179eada1c3 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -4060,6 +4060,7 @@ struct bpf_tcp_sock {
 	__u32 delivered;	/* Total data packets delivered incl. rexmits */
 	__u32 delivered_ce;	/* Like the above but only ECE marked packets */
 	__u32 icsk_retransmits;	/* Number of unrecovered [RTO] timeouts */
+	__u32 is_mptcp;		/* Is MPTCP subflow? */
 };
 
 struct bpf_sock_tuple {
diff --git a/net/core/filter.c b/net/core/filter.c
index d266c6941967..dab48528dceb 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5837,7 +5837,7 @@ bool bpf_tcp_sock_is_valid_access(int off, int size, enum bpf_access_type type,
 				  struct bpf_insn_access_aux *info)
 {
 	if (off < 0 || off >= offsetofend(struct bpf_tcp_sock,
-					  icsk_retransmits))
+					  is_mptcp))
 		return false;
 
 	if (off % size != 0)
@@ -5971,6 +5971,13 @@ u32 bpf_tcp_sock_convert_ctx_access(enum bpf_access_type type,
 	case offsetof(struct bpf_tcp_sock, icsk_retransmits):
 		BPF_INET_SOCK_GET_COMMON(icsk_retransmits);
 		break;
+	case offsetof(struct bpf_tcp_sock, is_mptcp):
+#ifdef CONFIG_MPTCP
+		BPF_TCP_SOCK_GET_COMMON(is_mptcp);
+#else
+		*insn++ = BPF_MOV32_IMM(si->dst_reg, 0);
+#endif
+		break;
 	}
 
 	return insn - insn_buf;
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 7dd314176df7..7d179eada1c3 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -4060,6 +4060,7 @@ struct bpf_tcp_sock {
 	__u32 delivered;	/* Total data packets delivered incl. rexmits */
 	__u32 delivered_ce;	/* Like the above but only ECE marked packets */
 	__u32 icsk_retransmits;	/* Number of unrecovered [RTO] timeouts */
+	__u32 is_mptcp;		/* Is MPTCP subflow? */
 };
 
 struct bpf_sock_tuple {
-- 
2.28.0


^ permalink raw reply related	[flat|nested] 14+ messages in thread
end of thread, other threads:[~2020-09-15 22:15 UTC | newest]

Thread overview: 14+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-09-11 14:30 [PATCH bpf-next v2 1/5] bpf: expose is_mptcp flag to bpf_tcp_sock Nicolas Rybowski
2020-09-11 14:30 ` [PATCH bpf-next v2 2/5] mptcp: attach subflow socket to parent cgroup Nicolas Rybowski
2020-09-14 20:52   ` Song Liu
2020-09-11 14:30 ` [PATCH bpf-next v2 3/5] bpf: add 'bpf_mptcp_sock' structure and helper Nicolas Rybowski
2020-09-14 21:00   ` Song Liu
2020-09-11 14:30 ` [PATCH bpf-next v2 4/5] bpf: selftests: add MPTCP test base Nicolas Rybowski
2020-09-14 18:07   ` Song Liu
2020-09-15 16:35     ` Nicolas Rybowski
2020-09-15 17:18       ` Song Liu
2020-09-11 14:30 ` [PATCH bpf-next v2 5/5] bpf: selftests: add bpf_mptcp_sock() verifier tests Nicolas Rybowski
2020-09-14 18:08   ` Song Liu
2020-09-11 14:30 ` [PATCH bpf-next v2 0/5] bpf: add MPTCP subflow support Nicolas Rybowski
2020-09-14 18:20 ` [PATCH bpf-next v2 1/5] bpf: expose is_mptcp flag to bpf_tcp_sock Song Liu
2020-09-14 22:13   ` Andrii Nakryiko

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