Commit f19397a5 authored by Lawrence Brakmo's avatar Lawrence Brakmo Committed by Daniel Borkmann
Browse files

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: default avatarLawrence Brakmo <brakmo@fb.com>
Acked-by: default avatarAlexei Starovoitov <ast@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent 792f3dd6

include/linux/filter.h

+1 −0
Original line number Diff line number Diff line
@@ -985,6 +985,7 @@ struct bpf_sock_ops_kern { 
		u32 reply;

		u32 replylong[4];

	};

	u32	is_fullsock;

};



#endif /* __LINUX_FILTER_H__ */

include/net/tcp.h

+4 −2
Original line number Diff line number Diff line
@@ -2012,10 +2012,12 @@ static inline int tcp_call_bpf(struct sock *sk, int op) 
	struct bpf_sock_ops_kern sock_ops;

	int ret;



	if (sk_fullsock(sk))

	memset(&sock_ops, 0, sizeof(sock_ops));

	if (sk_fullsock(sk)) {

		sock_ops.is_fullsock = 1;

		sock_owned_by_me(sk);

	}



	memset(&sock_ops, 0, sizeof(sock_ops));

	sock_ops.sk = sk;

	sock_ops.op = op;

include/uapi/linux/bpf.h

+6 −0
Original line number Diff line number Diff line
@@ -941,6 +941,12 @@ struct bpf_sock_ops { 
	__u32 local_ip6[4];	/* Stored in network byte order */

	__u32 remote_port;	/* Stored in network byte order */

	__u32 local_port;	/* stored in host byte order */

	__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 */

};



/* List of known BPF sock_ops operators.

net/core/filter.c

+36 −0
Original line number Diff line number Diff line
@@ -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;

}

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