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Date:   Tue, 19 Feb 2019 22:59:19 +0000
From:   Lawrence Brakmo <brakmo@...com>
To:     Daniel Borkmann <daniel@...earbox.net>,
        netdev <netdev@...r.kernel.org>
CC:     Martin Lau <kafai@...com>, Alexei Starovoitov <ast@...com>,
        "Daniel Borkmann --cc=Kernel Team" 
        <"daniel@...earbox.netKernel-team"@fb.com>
Subject: Re: [PATCH bpf-next 1/9] bpf: Add bpf helper bpf_tcp_enter_cwr


On 2/19/19, 2:24 AM, "Daniel Borkmann" <daniel@...earbox.net> wrote:

    On 02/19/2019 06:38 AM, brakmo wrote:
    > 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 typed bpf_prog
    > which currently can be attached to the ingress and egress
    > path.
    > 
    > 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.
    > 
    > Signed-off-by: Lawrence Brakmo <brakmo@...com>
    > Signed-off-by: Martin KaFai Lau <kafai@...com>
    > ---
    >  include/linux/bpf.h      |  1 +
    >  include/uapi/linux/bpf.h |  9 ++++++++-
    >  kernel/bpf/verifier.c    |  4 ++++
    >  net/core/filter.c        | 14 ++++++++++++++
    >  4 files changed, 27 insertions(+), 1 deletion(-)
    > 
    > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
    > index de18227b3d95..525628c913c9 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/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
    > index bcdd2474eee7..9e9f4f1a0370 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
    >   */
    >  #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/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 b584cb42a803..f51c4a781844 100644
    > --- a/net/core/filter.c
    > +++ b/net/core/filter.c
    > @@ -5426,6 +5426,18 @@ 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)
    > +{
    > +	tcp_enter_cwr((struct sock *)tp);
    
    Is it safe to call in every case, meaning do we always have a icsk_ca_ops
    assigned (e.g. pre-4whs completion)?

The helper, bpf_tcp_enter_cwr, can only be called for an skb belonging to a full tcp socket. The icsk_ca_ops field is initialized by tcp_init_sock, so this should not be an issue. However, it could be called before icsk_ca_ops->init() has been called, so it is probably better to check that the tcp sock is in the established state in the bpf helper.
    
    > +	return 0;
    > +}
    > +
    > +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 +5597,8 @@ cg_skb_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
    >  #ifdef CONFIG_INET
    >  	case BPF_FUNC_tcp_sock:
    >  		return &bpf_tcp_sock_proto;
    > +	case BPF_FUNC_tcp_enter_cwr:
    > +		return &bpf_tcp_enter_cwr_proto;
    >  #endif
    >  	default:
    >  		return sk_filter_func_proto(func_id, prog);
    > 
    
    

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