linux-kernel - RE: [PATCH 1/1] net: ioctl: Use kernel memory on protocol ioctl callbacks

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Message-ID: <f2d1a07b3e954db8ae40a2d739372e6c@AcuMS.aculab.com>
Date:   Fri, 19 May 2023 14:22:08 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Breno Leitao' <leitao@...ian.org>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "willemdebruijn.kernel@...il.com" <willemdebruijn.kernel@...il.com>,
        "courmisch@...il.com" <courmisch@...il.com>,
        "nhorman@...driver.com" <nhorman@...driver.com>
CC:     "asml.silence@...il.com" <asml.silence@...il.com>,
        "alex.aring@...il.com" <alex.aring@...il.com>,
        "dccp@...r.kernel.org" <dccp@...r.kernel.org>,
        "mptcp@...ts.linux.dev" <mptcp@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "matthieu.baerts@...sares.net" <matthieu.baerts@...sares.net>,
        "marcelo.leitner@...il.com" <marcelo.leitner@...il.com>,
        "linux-wpan@...r.kernel.org" <linux-wpan@...r.kernel.org>,
        "linux-sctp@...r.kernel.org" <linux-sctp@...r.kernel.org>,
        "leit@...com" <leit@...com>,
        "dsahern@...nel.org" <dsahern@...nel.org>
Subject: RE: [PATCH 1/1] net: ioctl: Use kernel memory on protocol ioctl
 callbacks

From: Breno Leitao
> Sent: 19 May 2023 14:58
> 
> 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).
> 
> This changes the "struct proto" ioctl format in the following way:
> 
>     int                     (*ioctl)(struct sock *sk, int cmd,
> -                                        unsigned long arg);
> +                                        int *karg);

I think I'd add a karg_len field for the actual buffer length.
It will save embarrassment later on.

Do any of the ioctl functions return +ve values on success?
If not you can use the return value as the length for any
copy_to_user().

If all the current 'cmd' are 16bit, there is the option
of using 32bit IOR() etc commands to get automatic sizing.

	David

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