linux-kernel - RE: [PATCH v2 2/8] io_uring/cmd: Introduce SOCKET_URING_OP

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Date:   Wed, 09 Aug 2023 09:21:04 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Breno Leitao <leitao@...ian.org>, sdf@...gle.com, axboe@...nel.dk,
        asml.silence@...il.com, willemdebruijn.kernel@...il.com
Cc:     bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, io-uring@...r.kernel.org, kuba@...nel.org,
        pabeni@...hat.com
Subject: RE: [PATCH v2 2/8] io_uring/cmd: Introduce SOCKET_URING_OP_GETSOCKOPT

Breno Leitao wrote:
> Add support for getsockopt command (SOCKET_URING_OP_GETSOCKOPT), where
> level is SOL_SOCKET. This is leveraging the sockptr_t infrastructure,
> where a sockptr_t is either userspace or kernel space, and handled as
> such.
> 
> Function io_uring_cmd_getsockopt() is inspired by __sys_getsockopt().
> 
> Differently from the getsockopt(2), the optlen field is not a userspace
> pointers. In getsockopt(2), userspace provides optlen pointer, which is
> overwritten by the kernel.  In this implementation, userspace passes a
> u32, and the new value is returned in cqe->res. I.e., optlen is not a
> pointer.
> 
> Important to say that userspace needs to keep the pointer alive until
> the CQE is completed.

What bad things can happen otherwise?

The kernel is not depending on a well behaved process for its
correctness here, is it? Any user pages have to be pinned while
kernel might refer to them, for instance.
 
> Signed-off-by: Breno Leitao <leitao@...ian.org>