[PATCH v2 bpf-next 2/9] bpf: Add bpf helper bpf_tcp_enter_cwr

[brakmo <brakmo@fb.com>]

From: Martin KaFai Lau <kafai@fb.com>

This patch adds a new bpf helper BPF_FUNC_tcp_enter_cwr
"int bpf_tcp_enter_cwr(struct bpf_tcp_sock *tp)".
It is added to BPF_PROG_TYPE_CGROUP_SKB which can be attached
to the egress path where the bpf prog is called by
ip_finish_output() or ip6_finish_output().  The verifier
ensures that the parameter must be a tcp_sock.

This helper makes a tcp_sock enter CWR state.  It can be used
by a bpf_prog to manage egress network bandwidth limit per
cgroupv2.  A later patch will have a sample program to
show how it can be used to limit bandwidth usage per cgroupv2.

To ensure it is only called from BPF_CGROUP_INET_EGRESS, the
attr->expected_attach_type must be specified as BPF_CGROUP_INET_EGRESS
during load time if the prog uses this new helper.
The newly added prog->enforce_expected_attach_type bit will also be set
if this new helper is used.  This bit is for backward compatibility reason
because currently prog->expected_attach_type has been ignored in
BPF_PROG_TYPE_CGROUP_SKB.  During attach time,
prog->expected_attach_type is only enforced if the
prog->enforce_expected_attach_type bit is set.
i.e. prog->expected_attach_type is only enforced if this new helper
is used by the prog.

Signed-off-by: Lawrence Brakmo <brakmo@fb.com>
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
---
 include/linux/bpf.h      |  1 +
 include/linux/filter.h   |  3 ++-
 include/uapi/linux/bpf.h |  9 ++++++++-
 kernel/bpf/syscall.c     | 12 ++++++++++++
 kernel/bpf/verifier.c    |  4 ++++
 net/core/filter.c        | 25 +++++++++++++++++++++++++
 6 files changed, 52 insertions(+), 2 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index d5ba2fc01af3..2d54ba7cf9dd 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -195,6 +195,7 @@ enum bpf_arg_type {
 	ARG_PTR_TO_SOCKET,	/* pointer to bpf_sock */
 	ARG_PTR_TO_SPIN_LOCK,	/* pointer to bpf_spin_lock */
 	ARG_PTR_TO_SOCK_COMMON,	/* pointer to sock_common */
+	ARG_PTR_TO_TCP_SOCK,    /* pointer to tcp_sock */
 };
 
 /* type of values returned from helper functions */
diff --git a/include/linux/filter.h b/include/linux/filter.h
index f32b3eca5a04..c6e878bdc5a6 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -510,7 +510,8 @@ struct bpf_prog {
 				blinded:1,	/* Was blinded */
 				is_func:1,	/* program is a bpf function */
 				kprobe_override:1, /* Do we override a kprobe? */
-				has_callchain_buf:1; /* callchain buffer allocated? */
+				has_callchain_buf:1, /* callchain buffer allocated? */
+				enforce_expected_attach_type:1; /* Enforce expected_attach_type checking at attach time */
 	enum bpf_prog_type	type;		/* Type of BPF program */
 	enum bpf_attach_type	expected_attach_type; /* For some prog types */
 	u32			len;		/* Number of filter blocks */
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index bcdd2474eee7..95b5058fa945 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -2359,6 +2359,12 @@ union bpf_attr {
  *	Return
  *		A **struct bpf_tcp_sock** pointer on success, or NULL in
  *		case of failure.
+ *
+ * int bpf_tcp_enter_cwr(struct bpf_tcp_sock *tp)
+ *	Description
+ *		Make a tcp_sock enter CWR state.
+ *	Return
+ *		0 on success, or a negative error in case of failure.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
@@ -2457,7 +2463,8 @@ union bpf_attr {
 	FN(spin_lock),			\
 	FN(spin_unlock),		\
 	FN(sk_fullsock),		\
-	FN(tcp_sock),
+	FN(tcp_sock),			\
+	FN(tcp_enter_cwr),
 
 /* integer value in 'imm' field of BPF_CALL instruction selects which helper
  * function eBPF program intends to call
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index ec7c552af76b..9a478f2875cd 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1482,6 +1482,14 @@ bpf_prog_load_check_attach_type(enum bpf_prog_type prog_type,
 		default:
 			return -EINVAL;
 		}
+	case BPF_PROG_TYPE_CGROUP_SKB:
+		switch (expected_attach_type) {
+		case BPF_CGROUP_INET_INGRESS:
+		case BPF_CGROUP_INET_EGRESS:
+			return 0;
+		default:
+			return -EINVAL;
+		}
 	default:
 		return 0;
 	}
@@ -1725,6 +1733,10 @@ static int bpf_prog_attach_check_attach_type(const struct bpf_prog *prog,
 	case BPF_PROG_TYPE_CGROUP_SOCK:
 	case BPF_PROG_TYPE_CGROUP_SOCK_ADDR:
 		return attach_type == prog->expected_attach_type ? 0 : -EINVAL;
+	case BPF_PROG_TYPE_CGROUP_SKB:
+		return prog->enforce_expected_attach_type &&
+			prog->expected_attach_type != attach_type ?
+			-EINVAL : 0;
 	default:
 		return 0;
 	}
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 1b9496c41383..95fb385c6f3c 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2424,6 +2424,10 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 regno,
 			return -EFAULT;
 		}
 		meta->ptr_id = reg->id;
+	} else if (arg_type == ARG_PTR_TO_TCP_SOCK) {
+		expected_type = PTR_TO_TCP_SOCK;
+		if (type != expected_type)
+			goto err_type;
 	} else if (arg_type == ARG_PTR_TO_SPIN_LOCK) {
 		if (meta->func_id == BPF_FUNC_spin_lock) {
 			if (process_spin_lock(env, regno, true))
diff --git a/net/core/filter.c b/net/core/filter.c
index 97916eedfe69..ca57ef25279c 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5426,6 +5426,24 @@ static const struct bpf_func_proto bpf_tcp_sock_proto = {
 	.arg1_type	= ARG_PTR_TO_SOCK_COMMON,
 };
 
+BPF_CALL_1(bpf_tcp_enter_cwr, struct tcp_sock *, tp)
+{
+	struct sock *sk = (struct sock *)tp;
+
+	if (sk->sk_state == TCP_ESTABLISHED) {
+		tcp_enter_cwr(sk);
+		return 0;
+	}
+
+	return -EINVAL;
+}
+
+static const struct bpf_func_proto bpf_tcp_enter_cwr_proto = {
+	.func        = bpf_tcp_enter_cwr,
+	.gpl_only    = false,
+	.ret_type    = RET_INTEGER,
+	.arg1_type    = ARG_PTR_TO_TCP_SOCK,
+};
 #endif /* CONFIG_INET */
 
 bool bpf_helper_changes_pkt_data(void *func)
@@ -5585,6 +5603,13 @@ cg_skb_func_proto(enum bpf_func_id func_id, struct bpf_prog *prog)
 #ifdef CONFIG_INET
 	case BPF_FUNC_tcp_sock:
 		return &bpf_tcp_sock_proto;
+	case BPF_FUNC_tcp_enter_cwr:
+		if (prog->expected_attach_type == BPF_CGROUP_INET_EGRESS) {
+			prog->enforce_expected_attach_type = 1;
+			return &bpf_tcp_enter_cwr_proto;
+		} else {
+			return NULL;
+		}
 #endif
 	default:
 		return sk_filter_func_proto(func_id, prog);
-- 
2.17.1