linux-kernel - Re: [PATCH net-next v3] net: ioctl: Use kernel memory on protocol ioctl callbacks

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Message-ID: <83d90ef3-67ba-737e-02fb-dbfb7cc8d2de@kernel.org>
Date:   Thu, 25 May 2023 09:03:02 -0600
From:   David Ahern <dsahern@...nel.org>
To:     Simon Horman <simon.horman@...igine.com>,
        Eric Dumazet <edumazet@...gle.com>
Cc:     Breno Leitao <leitao@...ian.org>, willemdebruijn.kernel@...il.com,
        Remi Denis-Courmont <courmisch@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Alexander Aring <alex.aring@...il.com>,
        Stefan Schmidt <stefan@...enfreihafen.org>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Matthieu Baerts <matthieu.baerts@...sares.net>,
        Mat Martineau <martineau@...nel.org>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Xin Long <lucien.xin@...il.com>, leit@...com, axboe@...nel.dk,
        asml.silence@...il.com, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, dccp@...r.kernel.org,
        linux-wpan@...r.kernel.org, mptcp@...ts.linux.dev,
        linux-sctp@...r.kernel.org
Subject: Re: [PATCH net-next v3] net: ioctl: Use kernel memory on protocol
 ioctl callbacks

On 5/25/23 8:54 AM, Simon Horman wrote:
> On Thu, May 25, 2023 at 04:19:32PM +0200, Eric Dumazet wrote:
>> On Thu, May 25, 2023 at 2:55 PM Breno Leitao <leitao@...ian.org> wrote:
>>>
>>> Most of the ioctls to net protocols operates directly on userspace
>>> argument (arg). Usually doing get_user()/put_user() directly in the
>>> ioctl callback.  This is not flexible, because it is hard to reuse these
>>> functions without passing userspace buffers.
>>>
>>> Change the "struct proto" ioctls to avoid touching userspace memory and
>>> operate on kernel buffers, i.e., all protocol's ioctl callbacks is
>>> adapted to operate on a kernel memory other than on userspace (so, no
>>> more {put,get}_user() and friends being called in the ioctl callback).
>>>
>>
>>  diff --git a/include/net/phonet/phonet.h b/include/net/phonet/phonet.h
>>> index 862f1719b523..93705d99f862 100644
>>> --- a/include/net/phonet/phonet.h
>>> +++ b/include/net/phonet/phonet.h
>>> @@ -109,4 +109,23 @@ void phonet_sysctl_exit(void);
>>>  int isi_register(void);
>>>  void isi_unregister(void);
>>>
>>> +#ifdef CONFIG_PHONET
>>> +int phonet_sk_ioctl(struct sock *sk, unsigned int cmd, void __user *arg);
>>> +
>>> +static inline bool phonet_is_sk(struct sock *sk)
>>> +{
>>> +       return sk->sk_family == PF_PHONET && sk->sk_protocol == PN_PROTO_PHONET;
>>> +}
>>> +#else
>>> +static inline bool phonet_is_sk(struct sock *sk)
>>> +{
>>> +       return 0;
>>> +}
>>> +
>>> +static inline int phonet_sk_ioctl(struct sock *sk, unsigned int cmd, void __user *arg)
>>> +{
>>> +       return 1;
>>> +}
>>> +#endif
>>> +
>>>
>>
>> PHONET can be built as a module, so I guess the compiler would
>> complain if "CONFIG_PHONET=m" ???
> 
> Yes, indeed it does.
> 

phonet_sk_ioctl is simple enough to make an inline in which case this
should go in include//linux/phonet.h.