linux-kernel - Re: [PATCH bpf-next] bpf: Clean code with bpf_copy_to

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Message-ID: <b4925bd4-8169-47c2-9cff-5a4023f07a32@linux.dev>
Date: Thu, 3 Jul 2025 08:35:51 -0700
From: Yonghong Song <yonghong.song@...ux.dev>
To: Tao Chen <chen.dylane@...ux.dev>, ast@...nel.org, daniel@...earbox.net,
 john.fastabend@...il.com, andrii@...nel.org, martin.lau@...ux.dev,
 eddyz87@...il.com, song@...nel.org, kpsingh@...nel.org, sdf@...ichev.me,
 haoluo@...gle.com, jolsa@...nel.org
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next] bpf: Clean code with bpf_copy_to_user



On 7/3/25 5:43 AM, Tao Chen wrote:
> No logic change, just use bpf_copy_to_user to clean code.
>
> Signed-off-by: Tao Chen <chen.dylane@...ux.dev>
> ---
>   kernel/bpf/syscall.c | 17 +++--------------
>   1 file changed, 3 insertions(+), 14 deletions(-)
>
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index e6eea594f1c..ca152d36312 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -5208,21 +5208,10 @@ static int bpf_task_fd_query_copy(const union bpf_attr *attr,
>   
>   			if (put_user(zero, ubuf))
>   				return -EFAULT;
> -		} else if (input_len >= len + 1) {
> -			/* ubuf can hold the string with NULL terminator */
> -			if (copy_to_user(ubuf, buf, len + 1))
> -				return -EFAULT;
>   		} else {
> -			/* ubuf cannot hold the string with NULL terminator,
> -			 * do a partial copy with NULL terminator.
> -			 */
> -			char zero = '\0';
> -
> -			err = -ENOSPC;
> -			if (copy_to_user(ubuf, buf, input_len - 1))
> -				return -EFAULT;
> -			if (put_user(zero, ubuf + input_len - 1))
> -				return -EFAULT;
> +			err = bpf_copy_to_user(ubuf, buf, input_len, len);
> +			if (err)
> +				return err;
>   		}
>   	}

Actually, there is a return value change with this patch.
bpf_copy_to_user() return returns -ENOSPC while the original
implementation may return -EFAULT due to following code.

         if (put_user(prog_id, &uattr->task_fd_query.prog_id) ||
             put_user(fd_type, &uattr->task_fd_query.fd_type) ||
             put_user(probe_offset, &uattr->task_fd_query.probe_offset) ||
             put_user(probe_addr, &uattr->task_fd_query.probe_addr))
                 return -EFAULT;

         return err;