Subject: Re: [PATCH v2 8/8] io_uring/cmd: BPF hook for setsockopt cmd

From: Martin KaFai Lau <[email-masked]>
Date: Wed, 9 Aug 2023 15:02:31 -0700

On 8/8/23 6:40 AM, Breno Leitao wrote:
> Add support for BPF hooks for io_uring setsockopts command.
> 
> This implementation follows a similar approach to what
> __sys_setsockopt() does, but, operates only on kernel memory instead of
> user memory (which is also possible, but not preferred since the kernel
> memory is already available)
> 
> Signed-off-by: Breno Leitao <[email-masked]>
> ---
>   io_uring/uring_cmd.c | 23 +++++++++++++++++++++--
>   1 file changed, 21 insertions(+), 2 deletions(-)
> 
> diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
> index 3693e5779229..b7b27e4dbddd 100644
> --- a/io_uring/uring_cmd.c
> +++ b/io_uring/uring_cmd.c
> @@ -205,23 +205,42 @@ static inline int io_uring_cmd_setsockopt(struct socket *sock,
>   {
>   	void __user *optval = u64_to_user_ptr(READ_ONCE(cmd->sqe->optval));
>   	int optname = READ_ONCE(cmd->sqe->optname);
> +	sockptr_t optval_s = USER_SOCKPTR(optval);
>   	int optlen = READ_ONCE(cmd->sqe->optlen);
>   	int level = READ_ONCE(cmd->sqe->level);
> +	char *kernel_optval = NULL;
>   	int err;
>   
>   	err = security_socket_setsockopt(sock, level, optname);
>   	if (err)
>   		return err;
>   
> +	if (!in_compat_syscall()) {
> +		err = BPF_CGROUP_RUN_PROG_SETSOCKOPT(sock->sk, &level,
> +						     &optname,
> +						     USER_SOCKPTR(optval),
> +						     &optlen,
> +						     &kernel_optval);
> +		if (err < 0)
> +			return err;
> +		if (err > 0)
> +			return 0;
> +
> +		/* Replace optval by the one returned by BPF */
> +		if (kernel_optval)
> +			optval_s = KERNEL_SOCKPTR(kernel_optval);
> +	}
> +
>   	if (level == SOL_SOCKET && !sock_use_custom_sol_socket(sock))
>   		err = sock_setsockopt(sock, level, optname,
> -				      USER_SOCKPTR(optval), optlen);
> +				      optval_s, optlen);
>   	else if (unlikely(!sock->ops->setsockopt))
>   		err = -EOPNOTSUPP;
>   	else
>   		err = sock->ops->setsockopt(sock, level, optname,
> -					    USER_SOCKPTR(koptval), optlen);
> +					    optval_s, optlen);

The bpf side changes make sense. Thanks.

With all the bpf pieces in place, __sys_{get,set}sockopt() is looking very 
similar to io_uring_cmd_{get,set}sockopt(). There are small differences like one 
takes fd and another already has a sock ptr, and io_uring_cmd_getsockopt() is 
SOL_SOCKET only. In general, can they be refactored somehow such that future 
changes don't have to be made in multiple places?