Re: [PATCH bpf-next] bpf: getsockopt hook to get optval without checking kernel retval

Martin KaFai Lau
2023-06-01T05:40:16Z

On 5/31/23 7:49 PM, Feng zhou wrote:
> From: Feng Zhou <zhoufeng.zf@bytedance.com>
>
> Remove the judgment on retval and pass bpf ctx by default. The
> advantage of this is that it is more flexible. Bpf getsockopt can
> support the new optname without using the module to call the
> nf_register_sockopt to register.
>
> Signed-off-by: Feng Zhou <zhoufeng.zf@bytedance.com>
> ---
> kernel/bpf/cgroup.c | 35 +++++++++++++----------------------
> 1 file changed, 13 insertions(+), 22 deletions(-)
>
> diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
> index 5b2741aa0d9b..ebad5442d8bb 100644
> --- a/kernel/bpf/cgroup.c
> +++ b/kernel/bpf/cgroup.c
> @@ -1896,30 +1896,21 @@ int __cgroup_bpf_run_filter_getsockopt(struct sock *sk, int level,
> if (max_optlen < 0)
> return max_optlen;
>
> - if (!retval) {
> - /* If kernel getsockopt finished successfully,
> - * copy whatever was returned to the user back
> - * into our temporary buffer. Set optlen to the
> - * one that kernel returned as well to let
> - * BPF programs inspect the value.
> - */
> -
> - if (get_user(ctx.optlen, optlen)) {
> - ret = -EFAULT;
> - goto out;
> - }
> + if (get_user(ctx.optlen, optlen)) {
> + ret = -EFAULT;
> + goto out;
> + }
>
> - if (ctx.optlen < 0) {
> - ret = -EFAULT;
> - goto out;
> - }
> - orig_optlen = ctx.optlen;
> + if (ctx.optlen < 0) {
> + ret = -EFAULT;
> + goto out;
> + }
> + orig_optlen = ctx.optlen;
>
> - if (copy_from_user(ctx.optval, optval,
> - min(ctx.optlen, max_optlen)) != 0) {
> - ret = -EFAULT;
> - goto out;
> - }
> + if (copy_from_user(ctx.optval, optval,
> + min(ctx.optlen, max_optlen)) != 0) {
What is in optval that is useful to copy from if the kernel didn't handle the
optname?

and there is no selftest also.

> + ret = -EFAULT;
> + goto out;
> }
>
> lock_sock(sk);