linux-kernel - Re: [PATCH linux-next] accessibility: speakup: use strscpy() to instead of strncpy()

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Message-ID: <20221203095644.6g7acpenj6brvjis@begin>
Date:   Sat, 3 Dec 2022 10:56:44 +0100
From:   Samuel Thibault <samuel.thibault@...-lyon.org>
To:     yang.yang29@....com.cn
Cc:     w.d.hubbs@...il.com, chris@...-brannons.com, kirk@...sers.ca,
        mushi.shar@...il.com, speakup@...ux-speakup.org,
        linux-kernel@...r.kernel.org, xu.panda@....com.cn
Subject: Re: [PATCH linux-next] accessibility: speakup: use strscpy() to
 instead of strncpy()

yang.yang29@....com.cn, le sam. 03 déc. 2022 14:21:28 +0800, a ecrit:
> From: Xu Panda <xu.panda@....com.cn>
> 
> The implementation of strscpy() is more robust and safer.
> That's now the recommended way to copy NUL terminated strings.
> 
> Signed-off-by: Xu Panda <xu.panda@....com.cn>
> Signed-off-by: Yang Yang <yang.yang29@....com>
> ---
>  drivers/accessibility/speakup/kobjects.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/accessibility/speakup/kobjects.c b/drivers/accessibility/speakup/kobjects.c
> index a7522d409802..273c076b661a 100644
> --- a/drivers/accessibility/speakup/kobjects.c
> +++ b/drivers/accessibility/speakup/kobjects.c
> @@ -426,8 +426,7 @@ static ssize_t synth_direct_store(struct kobject *kobj,
>  	spin_lock_irqsave(&speakup_info.spinlock, flags);
>  	while (len > 0) {
>  		bytes = min_t(size_t, len, 250);
> -		strncpy(tmp, ptr, bytes);
> -		tmp[bytes] = '\0';
> +		strscpy(tmp, ptr, bytes);

This needs to be bytes+1, otherwise the trailing `\0` will be put at
bytes-1 instead of bytes as the original code does, thus eating one
character.

>  		string_unescape_any_inplace(tmp);
>  		synth_printf("%s", tmp);
>  		ptr += bytes;
> -- 
> 2.15.2
>