linux-kernel - Re: [PATCH] fs: Replace offsetof() with struct_size() in ioctl_file_dedupe

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Message-ID: <65m5gqzejxjjeso2kxsu2pojdaylvv3z6nbl5lqimbxkz464ic@kc2nasscngeo>
Date: Fri, 29 Aug 2025 11:27:03 +0200
From: Jan Kara <jack@...e.cz>
To: Xichao Zhao <zhao.xichao@...o.com>
Cc: viro@...iv.linux.org.uk, brauner@...nel.org, mic@...ikod.net, 
	jack@...e.cz, gnoack@...gle.com, linux-fsdevel@...r.kernel.org, 
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs: Replace offsetof() with struct_size() in
 ioctl_file_dedupe_range()

On Fri 29-08-25 17:15:10, Xichao Zhao wrote:
> When dealing with structures containing flexible arrays, struct_size()
> provides additional compile-time checks compared to offsetof(). This
> enhances code robustness and reduces the risk of potential errors.
> 
> Signed-off-by: Xichao Zhao <zhao.xichao@...o.com>

Indeed. Also with struct_size() it is more obvious what was the intention.
Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/ioctl.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/ioctl.c b/fs/ioctl.c
> index 0248cb8db2d3..83d07218b6cd 100644
> --- a/fs/ioctl.c
> +++ b/fs/ioctl.c
> @@ -426,7 +426,7 @@ static int ioctl_file_dedupe_range(struct file *file,
>  		goto out;
>  	}
>  
> -	size = offsetof(struct file_dedupe_range, info[count]);
> +	size = struct_size(same, info, count);
>  	if (size > PAGE_SIZE) {
>  		ret = -ENOMEM;
>  		goto out;
> -- 
> 2.34.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR