netdev - Re: [PATCH bpf-next v3 09/15] bpf: add bpf_skc_to_udp6

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Message-ID: <a721817d-7382-f3d1-9cd0-7e6564b70f8b@fb.com>
Date:   Mon, 22 Jun 2020 19:22:03 -0700
From:   Yonghong Song <yhs@...com>
To:     Eric Dumazet <eric.dumazet@...il.com>, <bpf@...r.kernel.org>,
        <netdev@...r.kernel.org>
CC:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, <kernel-team@...com>,
        Martin KaFai Lau <kafai@...com>
Subject: Re: [PATCH bpf-next v3 09/15] bpf: add bpf_skc_to_udp6_sock() helper



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@...com>
>> Signed-off-by: Yonghong Song <yhs@...com>
>> ---
>>   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],
>> +};
[...]