linux-kernel - Re: [PATCH v4 00/10] io_uring: Initial support for {s,g}etsockopt commands

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Message-ID: <ZSArfLaaGcfd8LH8@gmail.com>
Date:   Fri, 6 Oct 2023 08:45:00 -0700
From:   Breno Leitao <leitao@...ian.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     sdf@...gle.com, axboe@...nel.dk, asml.silence@...il.com,
        willemdebruijn.kernel@...il.com, martin.lau@...ux.dev,
        krisman@...e.de, bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, io-uring@...r.kernel.org, pabeni@...hat.com
Subject: Re: [PATCH v4 00/10] io_uring: Initial support for {s,g}etsockopt
 commands

Hello Jakub,

On Tue, Sep 05, 2023 at 03:49:51PM -0700, Jakub Kicinski wrote:
> On Mon,  4 Sep 2023 09:24:53 -0700 Breno Leitao wrote:
> > Patches 1-2: Modify the BPF hooks to support sockptr_t, so, these functions
> > become flexible enough to accept user or kernel pointers for optval/optlen.
> 
> Have you seen:
> 
> https://lore.kernel.org/all/CAHk-=wgGV61xrG=gO0=dXH64o2TDWWrXn1mx-CX885JZ7h84Og@mail.gmail.com/
> 
> ? I wasn't aware that Linus felt this way, now I wonder if having
> sockptr_t spread will raise any red flags as this code flows back
> to him.

Thanks for the heads-up. I've been thinking about it for a while and I'd
like to hear what are the next steps here.

Let me first back up and state where we are, and what is the current
situation:

1) __sys_getsockopt() uses __user pointers for both optval and optlen
2) For io_uring command, Jens[1] suggested we get optlen from the io_uring
sqe, which is a kernel pointer/value.

Thus, we need to make the common code (callbacks) able to handle __user
and kernel pointers (for optlen, at least).

>From a proto_ops callback perspective, ->setsockopt() uses sockptr.

          int             (*setsockopt)(struct socket *sock, int level,
                                        int optname, sockptr_t optval,
                                        unsigned int optlen);

Getsockopt() uses sockptr() for level=SOL_SOCKET:

	int sk_getsockopt(struct sock *sk, int level, int optname,
                    sockptr_t optval, sockptr_t optlen)

But not for the other levels:

	int             (*getsockopt)(struct socket *sock, int level,
				      int optname, char __user *optval, int __user *optlen);

That said, if this patchset shouldn't use sockptr anymore, what is the
recommendation?

If we move this patchset to use iov_iter instead of sockptr, then I
understand we want to move *all* these callbacks to use iov_vec. Is this
the right direction?

Thanks for the guidance!

[1] https://lore.kernel.org/all/efe602f1-8e72-466c-b796-0083fd1c6d82@kernel.dk/