bpf: Add access to snd_cwnd and others in sock_ops

Adds read access to snd_cwnd and srtt_us fields of tcp_sock. Since these
fields are only valid if the socket associated with the sock_ops program
call is a full socket, the field is_fullsock is also added to the
bpf_sock_ops struct. If the socket is not a full socket, reading these
fields returns 0.

Note that in most cases it will not be necessary to check is_fullsock to
know if there is a full socket. The context of the call, as specified by
the 'op' field, can sometimes determine whether there is a full socket.

The struct bpf_sock_ops has the following fields added:

  __u32 is_fullsock;      /* Some TCP fields are only valid if
                           * there is a full socket. If not, the
                           * fields read as zero.
			   */
  __u32 snd_cwnd;
  __u32 srtt_us;          /* Averaged RTT << 3 in usecs */

There is a new macro, SOCK_OPS_GET_TCP32(NAME), to make it easier to add
read access to more 32 bit tcp_sock fields.

Signed-off-by: Lawrence Brakmo <brakmo@fb.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 36 insertions, 0 deletions

diff --git a/net/core/filter.c b/net/core/filter.c
index 4d644ad..754abe1 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -4437,6 +4437,42 @@ static u32 sock_ops_convert_ctx_access(enum bpf_access_type type,
 		*insn++ = BPF_LDX_MEM(BPF_H, si->dst_reg, si->dst_reg,
 				      offsetof(struct sock_common, skc_num));
 		break;
+
+	case offsetof(struct bpf_sock_ops, is_fullsock):
+		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(
+						struct bpf_sock_ops_kern,
+						is_fullsock),
+				      si->dst_reg, si->src_reg,
+				      offsetof(struct bpf_sock_ops_kern,
+					       is_fullsock));
+		break;
+
+/* Helper macro for adding read access to tcp_sock fields. */
+#define SOCK_OPS_GET_TCP32(FIELD_NAME)					      \
+	do {								      \
+		BUILD_BUG_ON(FIELD_SIZEOF(struct tcp_sock, FIELD_NAME) != 4); \
+		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(			      \
+						struct bpf_sock_ops_kern,     \
+						is_fullsock),		      \
+				      si->dst_reg, si->src_reg,		      \
+				      offsetof(struct bpf_sock_ops_kern,      \
+					       is_fullsock));		      \
+		*insn++ = BPF_JMP_IMM(BPF_JEQ, si->dst_reg, 0, 2);	      \
+		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(			      \
+						struct bpf_sock_ops_kern, sk),\
+				      si->dst_reg, si->src_reg,		      \
+				      offsetof(struct bpf_sock_ops_kern, sk));\
+		*insn++ = BPF_LDX_MEM(BPF_W, si->dst_reg, si->dst_reg,        \
+				      offsetof(struct tcp_sock, FIELD_NAME)); \
+	} while (0)
+
+	case offsetof(struct bpf_sock_ops, snd_cwnd):
+		SOCK_OPS_GET_TCP32(snd_cwnd);
+		break;
+
+	case offsetof(struct bpf_sock_ops, srtt_us):
+		SOCK_OPS_GET_TCP32(srtt_us);
+		break;
 	}
 	return insn - insn_buf;
 }