bpf: add icsk_retransmits to bpf_tcp_sock

Add some inet_connection_sock fields to bpf_tcp_sock that might be useful
for debugging congestion control issues.

Cc: Eric Dumazet <edumazet@google.com>
Cc: Priyaranjan Jha <priyarjha@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

include/uapi/linux/bpf.h

@@ -3078,6 +3078,7 @@ 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 */
 };
 
 struct bpf_sock_tuple {

net/core/filter.c

@@ -5544,7 +5544,8 @@ static const struct bpf_func_proto bpf_sock_addr_sk_lookup_udp_proto = {
 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, delivered_ce))
+	if (off < 0 || off >= offsetofend(struct bpf_tcp_sock,
+					  icsk_retransmits))
 		return false;
 
 	if (off % size != 0)
@@ -5575,6 +5576,20 @@ u32 bpf_tcp_sock_convert_ctx_access(enum bpf_access_type type,
 				      offsetof(struct tcp_sock, FIELD)); \
 	} while (0)
 
+#define BPF_INET_SOCK_GET_COMMON(FIELD)					\
+	do {								\
+		BUILD_BUG_ON(FIELD_SIZEOF(struct inet_connection_sock,	\
+					  FIELD) >			\
+			     FIELD_SIZEOF(struct bpf_tcp_sock, FIELD));	\
+		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(			\
+					struct inet_connection_sock,	\
+					FIELD),				\
+				      si->dst_reg, si->src_reg,		\
+				      offsetof(				\
+					struct inet_connection_sock,	\
+					FIELD));			\
+	} while (0)
+
 	if (insn > insn_buf)
 		return insn - insn_buf;
 
@@ -5661,6 +5676,9 @@ u32 bpf_tcp_sock_convert_ctx_access(enum bpf_access_type type,
 	case offsetof(struct bpf_tcp_sock, delivered_ce):
 		BPF_TCP_SOCK_GET_COMMON(delivered_ce);
 		break;
+	case offsetof(struct bpf_tcp_sock, icsk_retransmits):
+		BPF_INET_SOCK_GET_COMMON(icsk_retransmits);
+		break;
 	}
 
 	return insn - insn_buf;