Re: [PATCH bpf-next v3 09/15] bpf: add bpf_skc_to_udp6_sock() helper

[Yonghong Song <yhs@xxxxxx>]

On 6/22/20 6:47 PM, Eric Dumazet wrote:
> On 6/22/20 5:36 PM, Yonghong Song wrote:
> > The helper is used in tracing programs to cast a socket
> > pointer to a udp6_sock pointer.
> > The return value could be NULL if the casting is illegal.
> >
> > Acked-by: Martin KaFai Lau <kafai@xxxxxx>
> > Signed-off-by: Yonghong Song <yhs@xxxxxx>
> > ---
> >   include/linux/bpf.h            |  1 +
> >   include/uapi/linux/bpf.h       |  9 ++++++++-
> >   kernel/trace/bpf_trace.c       |  2 ++
> >   net/core/filter.c              | 22 ++++++++++++++++++++++
> >   scripts/bpf_helpers_doc.py     |  2 ++
> >   tools/include/uapi/linux/bpf.h |  9 ++++++++-
> >   6 files changed, 43 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index cc3f89827b89..3f5c6bb5e3a7 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -1649,6 +1649,7 @@ extern const struct bpf_func_proto bpf_skc_to_tcp6_sock_proto;
> >   extern const struct bpf_func_proto bpf_skc_to_tcp_sock_proto;
> >   extern const struct bpf_func_proto bpf_skc_to_tcp_timewait_sock_proto;
> >   extern const struct bpf_func_proto bpf_skc_to_tcp_request_sock_proto;
> > +extern const struct bpf_func_proto bpf_skc_to_udp6_sock_proto;
> >   
> >   const struct bpf_func_proto *bpf_tracing_func_proto(
> >   	enum bpf_func_id func_id, const struct bpf_prog *prog);
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index e256417d94c2..3f4b12c5c563 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -3276,6 +3276,12 @@ union bpf_attr {
> >    *		Dynamically cast a *sk* pointer to a *tcp_request_sock* pointer.
> >    *	Return
> >    *		*sk* if casting is valid, or NULL otherwise.
> > + *
> > + * struct udp6_sock *bpf_skc_to_udp6_sock(void *sk)
> > + * 	Description
> > + *		Dynamically cast a *sk* pointer to a *udp6_sock* pointer.
> > + *	Return
> > + *		*sk* if casting is valid, or NULL otherwise.
> >    */
> >   #define __BPF_FUNC_MAPPER(FN)		\
> >   	FN(unspec),			\
> > @@ -3417,7 +3423,8 @@ union bpf_attr {
> >   	FN(skc_to_tcp6_sock),		\
> >   	FN(skc_to_tcp_sock),		\
> >   	FN(skc_to_tcp_timewait_sock),	\
> > -	FN(skc_to_tcp_request_sock),
> > +	FN(skc_to_tcp_request_sock),	\
> > +	FN(skc_to_udp6_sock),
> >   
> >   /* integer value in 'imm' field of BPF_CALL instruction selects which helper
> >    * function eBPF program intends to call
> > diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> > index de5fbe66e1ca..d10ab16c4a2f 100644
> > --- a/kernel/trace/bpf_trace.c
> > +++ b/kernel/trace/bpf_trace.c
> > @@ -1523,6 +1523,8 @@ tracing_prog_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
> >   		return &bpf_skc_to_tcp_timewait_sock_proto;
> >   	case BPF_FUNC_skc_to_tcp_request_sock:
> >   		return &bpf_skc_to_tcp_request_sock_proto;
> > +	case BPF_FUNC_skc_to_udp6_sock:
> > +		return &bpf_skc_to_udp6_sock_proto;
> >   #endif
> >   	case BPF_FUNC_seq_printf:
> >   		return prog->expected_attach_type == BPF_TRACE_ITER ?
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index 140fc0fdf3e1..9a98f3616273 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> > @@ -9325,3 +9325,25 @@ const struct bpf_func_proto bpf_skc_to_tcp_request_sock_proto = {
> >   	.check_btf_id		= check_arg_btf_id,
> >   	.ret_btf_id		= &btf_sock_ids[BTF_SOCK_TYPE_TCP_REQ],
> >   };
> > +
> > +BPF_CALL_1(bpf_skc_to_udp6_sock, struct sock *, sk)
> > +{
> > +	/* udp6_sock type is not generated in dwarf and hence btf,
> > +	 * trigger an explicit type generation here.
> > +	 */
> > +	BTF_TYPE_EMIT(struct udp6_sock);
> > +	if (sk_fullsock(sk) && sk->sk_protocol == IPPROTO_UDP &&
>
> Why is the sk_fullsock(sk) needed ?

The parameter 'sk' could be a sock_common. That is why the
helper name bpf_skc_to_udp6_sock implies. The sock_common cannot
access sk_protocol, hence we requires sk_fullsock(sk) here.
Did I miss anything?

> > +	    sk->sk_family == AF_INET6)
> > +		return (unsigned long)sk;
> > +
> > +	return (unsigned long)NULL;
> > +}
> > +
> > +const struct bpf_func_proto bpf_skc_to_udp6_sock_proto = {
> > +	.func			= bpf_skc_to_udp6_sock,
> > +	.gpl_only		= false,
> > +	.ret_type		= RET_PTR_TO_BTF_ID_OR_NULL,
> > +	.arg1_type		= ARG_PTR_TO_BTF_ID,
> > +	.check_btf_id		= check_arg_btf_id,
> > +	.ret_btf_id		= &btf_sock_ids[BTF_SOCK_TYPE_UDP6],
> > +};
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