linux-kernel - Re: [PATCH] HID: prodikeys: refactor deprecated strncpy

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Message-ID: <202309142201.683ED5A7FD@keescook>
Date:   Thu, 14 Sep 2023 22:02:12 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH] HID: prodikeys: refactor deprecated strncpy

On Thu, Sep 14, 2023 at 10:20:55PM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> We should prefer more robust and less ambiguous string interfaces.
> 
> A suitable replacement is `strscpy` [2] due to the fact that it guarantees
> NUL-termination on the destination buffer without unnecessarily NUL-padding.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://manpages.debian.org/testing/linux-manual-4.8/strscpy.9.en.html [2]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@...r.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@...gle.com>
> ---
> Note: for some reason if NUL-padding is needed let's opt for `strscpy_pad()`
> ---
>  drivers/hid/hid-prodikeys.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/hid/hid-prodikeys.c b/drivers/hid/hid-prodikeys.c
> index e4e9471d0f1e..c16d2ba6ea16 100644
> --- a/drivers/hid/hid-prodikeys.c
> +++ b/drivers/hid/hid-prodikeys.c
> @@ -639,9 +639,9 @@ static int pcmidi_snd_initialise(struct pcmidi_snd *pm)
>  		goto fail;
>  	}
>  
> -	strncpy(card->driver, shortname, sizeof(card->driver));
> -	strncpy(card->shortname, shortname, sizeof(card->shortname));
> -	strncpy(card->longname, longname, sizeof(card->longname));
> +	strscpy(card->driver, shortname, sizeof(card->driver));
> +	strscpy(card->shortname, shortname, sizeof(card->shortname));
> +	strscpy(card->longname, longname, sizeof(card->longname));

"card" is already kzalloc()ed so no _pad() is needed, good.

>  
>  	/* Set up rawmidi */
>  	err = snd_rawmidi_new(card, card->shortname, 0,
> @@ -652,7 +652,7 @@ static int pcmidi_snd_initialise(struct pcmidi_snd *pm)
>  		goto fail;
>  	}
>  	pm->rwmidi = rwmidi;
> -	strncpy(rwmidi->name, card->shortname, sizeof(rwmidi->name));
> +	strscpy(rwmidi->name, card->shortname, sizeof(rwmidi->name));
>  	rwmidi->info_flags = SNDRV_RAWMIDI_INFO_INPUT;
>  	rwmidi->private_data = pm;

Same here.

Reviewed-by: Kees Cook <keescook@...omium.org>

-Kees

>  
> 
> ---
> base-commit: 3669558bdf354cd352be955ef2764cde6a9bf5ec
> change-id: 20230914-strncpy-drivers-hid-hid-prodikeys-c-cf42614a21d4
> 
> Best regards,
> --
> Justin Stitt <justinstitt@...gle.com>
> 

-- 
Kees Cook