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

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Date:   Thu, 25 May 2023 16:19:32 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Breno Leitao <leitao@...ian.org>
Cc:     dsahern@...nel.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 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" ???