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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>
This commit is contained in:
Lawrence Brakmo 2017-12-01 10:15:04 -08:00 committed by Daniel Borkmann
parent 792f3dd6f0
commit f19397a5c6
4 changed files with 48 additions and 3 deletions
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1
include/linux/filter.h
View File

@ -985,6 +985,7 @@ struct bpf_sock_ops_kern {
u32 reply;
u32 replylong[4];
};
u32 is_fullsock;
};
#endif /* __LINUX_FILTER_H__ */

8
include/net/tcp.h
View File

@ -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))
sock_owned_by_me(sk);
memset(&sock_ops, 0, sizeof(sock_ops));
if (sk_fullsock(sk)) {
sock_ops.is_fullsock = 1;
sock_owned_by_me(sk);
}
sock_ops.sk = sk;
sock_ops.op = op;

6
include/uapi/linux/bpf.h
View File

@ -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.

36
net/core/filter.c
View File

@ -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;
}