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>

diff --git a/include/linux/filter.h b/include/linux/filter.h
index 80b5b48..0062302 100644 (file)
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -985,6 +985,7 @@ struct bpf_sock_ops_kern {
                u32 reply;
                u32 replylong[4];
        };
+       u32     is_fullsock;
 };
 
 #endif /* __LINUX_FILTER_H__ */

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 4e09398..89a6560 100644 (file)
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -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;
 

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 4c223ab..80d62e8 100644 (file)
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -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.

diff --git a/net/core/filter.c b/net/core/filter.c
index 4d644ad..754abe1 100644 (file)
--- 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;
 }