[bpf-next,v14,1/4] bpf: Add update_socket_protocol hook

Commit Message

Geliang Tang Aug. 16, 2023, 1:11 a.m. UTC

Add a hook named update_socket_protocol in __sys_socket(), for bpf
progs to attach to and update socket protocol. One user case is to
force legacy TCP apps to create and use MPTCP sockets instead of
TCP ones.

Define a fmod_ret set named bpf_mptcp_fmodret_ids, add the hook
update_socket_protocol into this set, and register it in
bpf_mptcp_kfunc_init().

Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/79
Acked-by: Matthieu Baerts <[e-mail]>
Acked-by: Yonghong Song <[e-mail]>
Signed-off-by: Geliang Tang <[e-mail]>
---
 net/mptcp/bpf.c | 15 +++++++++++++++
 net/socket.c    | 26 +++++++++++++++++++++++++-
 2 files changed, 40 insertions(+), 1 deletion(-)

Comments

Geliang Tang Aug. 18, 2023, 8:24 a.m. UTC | #1

On Wed, Aug 16, 2023 at 09:11:56AM +0800, Geliang Tang wrote:
> Add a hook named update_socket_protocol in __sys_socket(), for bpf
> progs to attach to and update socket protocol. One user case is to
> force legacy TCP apps to create and use MPTCP sockets instead of
> TCP ones.
> 
> Define a fmod_ret set named bpf_mptcp_fmodret_ids, add the hook
> update_socket_protocol into this set, and register it in
> bpf_mptcp_kfunc_init().
> 
> Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/79
> Acked-by: Matthieu Baerts <[e-mail]>
> Acked-by: Yonghong Song <[e-mail]>
> Signed-off-by: Geliang Tang <[e-mail]>
> ---
>  net/mptcp/bpf.c | 15 +++++++++++++++
>  net/socket.c    | 26 +++++++++++++++++++++++++-
>  2 files changed, 40 insertions(+), 1 deletion(-)
> 
> diff --git a/net/mptcp/bpf.c b/net/mptcp/bpf.c
> index 5a0a84ad94af..8a16672b94e2 100644
> --- a/net/mptcp/bpf.c
> +++ b/net/mptcp/bpf.c
> @@ -19,3 +19,18 @@ struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk)
>  
>  	return NULL;
>  }
> +
> +BTF_SET8_START(bpf_mptcp_fmodret_ids)
> +BTF_ID_FLAGS(func, update_socket_protocol)
> +BTF_SET8_END(bpf_mptcp_fmodret_ids)
> +
> +static const struct btf_kfunc_id_set bpf_mptcp_fmodret_set = {
> +	.owner = THIS_MODULE,
> +	.set   = &bpf_mptcp_fmodret_ids,
> +};
> +
> +static int __init bpf_mptcp_kfunc_init(void)
> +{
> +	return register_btf_fmodret_id_set(&bpf_mptcp_fmodret_set);
> +}
> +late_initcall(bpf_mptcp_kfunc_init);
> diff --git a/net/socket.c b/net/socket.c
> index 5d4e37595e9a..fdb5233bf560 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -1657,12 +1657,36 @@ struct file *__sys_socket_file(int family, int type, int protocol)
>  	return sock_alloc_file(sock, flags, NULL);
>  }
>  
> +/*	A hook for bpf progs to attach to and update socket protocol.
> + *
> + *	A static noinline declaration here could cause the compiler to
> + *	optimize away the function. A global noinline declaration will
> + *	keep the definition, but may optimize away the callsite.
> + *	Therefore, __weak is needed to ensure that the call is still
> + *	emitted, by telling the compiler that we don't know what the
> + *	function might eventually be.
> + *
> + *	__diag_* below are needed to dismiss the missing prototype warning.
> + */
> +
> +__diag_push();
> +__diag_ignore_all("-Wmissing-prototypes",
> +		  "A fmod_ret entry point for BPF programs");

Hi Martin & Yonghong,

I got a sparse warning for this new added 'update_socket_protocol':

 > touch net/socket.c && make C=1 net/socket.o

 net/socket.c:1676:21: warning: symbol 'update_socket_protocol' was not declared. Should it be static?

What should I do to fix it, or should I just leave it here? Please give
me some suggestions.

Thanks,
-Geliang

> +
> +__weak noinline int update_socket_protocol(int family, int type, int protocol)
> +{
> +	return protocol;
> +}
> +
> +__diag_pop();
> +
>  int __sys_socket(int family, int type, int protocol)
>  {
>  	struct socket *sock;
>  	int flags;
>  
> -	sock = __sys_socket_create(family, type, protocol);
> +	sock = __sys_socket_create(family, type,
> +				   update_socket_protocol(family, type, protocol));
>  	if (IS_ERR(sock))
>  		return PTR_ERR(sock);
>  
> -- 
> 2.35.3
>

Yonghong Song Aug. 18, 2023, 3:26 p.m. UTC | #2

On 8/18/23 1:24 AM, Geliang Tang wrote:
> On Wed, Aug 16, 2023 at 09:11:56AM +0800, Geliang Tang wrote:
>> Add a hook named update_socket_protocol in __sys_socket(), for bpf
>> progs to attach to and update socket protocol. One user case is to
>> force legacy TCP apps to create and use MPTCP sockets instead of
>> TCP ones.
>>
>> Define a fmod_ret set named bpf_mptcp_fmodret_ids, add the hook
>> update_socket_protocol into this set, and register it in
>> bpf_mptcp_kfunc_init().
>>
>> Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/79
>> Acked-by: Matthieu Baerts <[e-mail]>
>> Acked-by: Yonghong Song <[e-mail]>
>> Signed-off-by: Geliang Tang <[e-mail]>
>> ---
>>   net/mptcp/bpf.c | 15 +++++++++++++++
>>   net/socket.c    | 26 +++++++++++++++++++++++++-
>>   2 files changed, 40 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/mptcp/bpf.c b/net/mptcp/bpf.c
>> index 5a0a84ad94af..8a16672b94e2 100644
>> --- a/net/mptcp/bpf.c
>> +++ b/net/mptcp/bpf.c
>> @@ -19,3 +19,18 @@ struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk)
>>   
>>   	return NULL;
>>   }
>> +
>> +BTF_SET8_START(bpf_mptcp_fmodret_ids)
>> +BTF_ID_FLAGS(func, update_socket_protocol)
>> +BTF_SET8_END(bpf_mptcp_fmodret_ids)
>> +
>> +static const struct btf_kfunc_id_set bpf_mptcp_fmodret_set = {
>> +	.owner = THIS_MODULE,
>> +	.set   = &bpf_mptcp_fmodret_ids,
>> +};
>> +
>> +static int __init bpf_mptcp_kfunc_init(void)
>> +{
>> +	return register_btf_fmodret_id_set(&bpf_mptcp_fmodret_set);
>> +}
>> +late_initcall(bpf_mptcp_kfunc_init);
>> diff --git a/net/socket.c b/net/socket.c
>> index 5d4e37595e9a..fdb5233bf560 100644
>> --- a/net/socket.c
>> +++ b/net/socket.c
>> @@ -1657,12 +1657,36 @@ struct file *__sys_socket_file(int family, int type, int protocol)
>>   	return sock_alloc_file(sock, flags, NULL);
>>   }
>>   
>> +/*	A hook for bpf progs to attach to and update socket protocol.
>> + *
>> + *	A static noinline declaration here could cause the compiler to
>> + *	optimize away the function. A global noinline declaration will
>> + *	keep the definition, but may optimize away the callsite.
>> + *	Therefore, __weak is needed to ensure that the call is still
>> + *	emitted, by telling the compiler that we don't know what the
>> + *	function might eventually be.
>> + *
>> + *	__diag_* below are needed to dismiss the missing prototype warning.
>> + */
>> +
>> +__diag_push();
>> +__diag_ignore_all("-Wmissing-prototypes",
>> +		  "A fmod_ret entry point for BPF programs");
> 
> Hi Martin & Yonghong,
> 
> I got a sparse warning for this new added 'update_socket_protocol':
> 
>   > touch net/socket.c && make C=1 net/socket.o
> 
>   net/socket.c:1676:21: warning: symbol 'update_socket_protocol' was not declared. Should it be static?

This is a sparse warning. Let us ignore it for now. We already have
__diag_ignore for missing prototypes in the above, but sparse won't 
recognize them. Also, 'static' is conflict with '__weak' attribute,
and we cannot remove '__weak' attribute.

> 
> What should I do to fix it, or should I just leave it here? Please give
> me some suggestions.
> 
> Thanks,
> -Geliang
> 
>> +
>> +__weak noinline int update_socket_protocol(int family, int type, int protocol)
>> +{
>> +	return protocol;
>> +}
>> +
>> +__diag_pop();
>> +
>>   int __sys_socket(int family, int type, int protocol)
>>   {
>>   	struct socket *sock;
>>   	int flags;
>>   
>> -	sock = __sys_socket_create(family, type, protocol);
>> +	sock = __sys_socket_create(family, type,
>> +				   update_socket_protocol(family, type, protocol));
>>   	if (IS_ERR(sock))
>>   		return PTR_ERR(sock);
>>   
>> -- 
>> 2.35.3
>>
>

Patch

diff --git a/net/mptcp/bpf.c b/net/mptcp/bpf.c
index 5a0a84ad94af..8a16672b94e2 100644
--- a/net/mptcp/bpf.c
+++ b/net/mptcp/bpf.c
@@ -19,3 +19,18 @@  struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk)
 
 	return NULL;
 }
+
+BTF_SET8_START(bpf_mptcp_fmodret_ids)
+BTF_ID_FLAGS(func, update_socket_protocol)
+BTF_SET8_END(bpf_mptcp_fmodret_ids)
+
+static const struct btf_kfunc_id_set bpf_mptcp_fmodret_set = {
+	.owner = THIS_MODULE,
+	.set   = &bpf_mptcp_fmodret_ids,
+};
+
+static int __init bpf_mptcp_kfunc_init(void)
+{
+	return register_btf_fmodret_id_set(&bpf_mptcp_fmodret_set);
+}
+late_initcall(bpf_mptcp_kfunc_init);
diff --git a/net/socket.c b/net/socket.c
index 5d4e37595e9a..fdb5233bf560 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -1657,12 +1657,36 @@  struct file *__sys_socket_file(int family, int type, int protocol)
 	return sock_alloc_file(sock, flags, NULL);
 }
 
+/*	A hook for bpf progs to attach to and update socket protocol.
+ *
+ *	A static noinline declaration here could cause the compiler to
+ *	optimize away the function. A global noinline declaration will
+ *	keep the definition, but may optimize away the callsite.
+ *	Therefore, __weak is needed to ensure that the call is still
+ *	emitted, by telling the compiler that we don't know what the
+ *	function might eventually be.
+ *
+ *	__diag_* below are needed to dismiss the missing prototype warning.
+ */
+
+__diag_push();
+__diag_ignore_all("-Wmissing-prototypes",
+		  "A fmod_ret entry point for BPF programs");
+
+__weak noinline int update_socket_protocol(int family, int type, int protocol)
+{
+	return protocol;
+}
+
+__diag_pop();
+
 int __sys_socket(int family, int type, int protocol)
 {
 	struct socket *sock;
 	int flags;
 
-	sock = __sys_socket_create(family, type, protocol);
+	sock = __sys_socket_create(family, type,
+				   update_socket_protocol(family, type, protocol));
 	if (IS_ERR(sock))
 		return PTR_ERR(sock);