linux-kernel - Re: [PATCH bpf-next 2/2] bpf: Check link_create parameter for multi

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Message-ID: <Z-vH_HiJhR3cwLhF@krava>
Date: Tue, 1 Apr 2025 13:03:24 +0200
From: Jiri Olsa <olsajiri@...il.com>
To: Tao Chen <chen.dylane@...ux.dev>
Cc: song@...nel.org, ast@...nel.org, daniel@...earbox.net,
	andrii@...nel.org, martin.lau@...ux.dev, eddyz87@...il.com,
	yonghong.song@...ux.dev, john.fastabend@...il.com,
	kpsingh@...nel.org, sdf@...ichev.me, haoluo@...gle.com,
	rostedt@...dmis.org, mhiramat@...nel.org,
	mathieu.desnoyers@...icios.com, laoar.shao@...il.com,
	bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next 2/2] bpf: Check link_create parameter for
 multi_uprobe

On Mon, Mar 31, 2025 at 05:47:45PM +0800, Tao Chen wrote:
> The target_fd and flags in link_create no used in multi_uprobe
> , return -EINVAL if they assigned, keep it same as other link
> attach apis.
> 
> Fixes: 89ae89f53d20 ("bpf: Add multi uprobe link")
> Signed-off-by: Tao Chen <chen.dylane@...ux.dev>
> ---
>  kernel/trace/bpf_trace.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 2f206a2a2..f7ebf17e3 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -3385,6 +3385,9 @@ int bpf_uprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
>  	if (sizeof(u64) != sizeof(void *))
>  		return -EOPNOTSUPP;
>  
> +	if (attr->link_create.target_fd || attr->link_create.flags)
> +		return -EINVAL;

I think the CI is failing because usdt code does uprobe multi detection
with target_fd = -1 and it fails and perf-uprobe fallback will fail on
not having enough file descriptors

but I think at this stage we will brake some user apps by introducing
this check, link ebpf go library, which passes 0

jirka


> +
>  	if (!is_uprobe_multi(prog))
>  		return -EINVAL;
>  
> -- 
> 2.43.0
>