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Sender: Corey Minyard <tcminyard@gmail.com>
Date:   Tue, 12 Sep 2023 19:19:25 -0500
From:   Corey Minyard <minyard@acm.org>
To:     Justin Stitt <justinstitt@google.com>
Cc:     openipmi-developer@lists.sourceforge.net,
        linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org,
        Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH] ipmi: refactor deprecated strncpy
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References: <20230912-strncpy-drivers-char-ipmi-ipmi-v1-1-cc43e0d1cae6@google.com>
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On Tue, Sep 12, 2023 at 11:43:05PM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> In this case, strncpy is being used specifically for its NUL-padding
> behavior (and has been commented as such). We can use a more robust and
> less ambiguous interface in `strscpy_pad` which makes the code more
> readable and even eliminates the need for that comment.
> 
> Let's also use `strnlen` instead of `strlen()` with an upper-bounds
> check as this is intrinsically a part of `strnlen`.
> 
> Also included in this patch is a simple 1:1 change of `strncpy` to
> `strscpy` for ipmi_ssif.c. If NUL-padding is wanted here as well then we
> should opt again for `strscpy_pad`.
> 
> Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#strncpy-on-nul-terminated-strings [1]
> Link: https://github.com/KSPP/linux/issues/90
> Cc: linux-hardening@vger.kernel.org
> Cc: Kees Cook <keescook@chromium.org>
> Signed-off-by: Justin Stitt <justinstitt@google.com>
> ---
>  drivers/char/ipmi/ipmi_msghandler.c | 11 +++--------
>  drivers/char/ipmi/ipmi_ssif.c       |  2 +-
>  2 files changed, 4 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/char/ipmi/ipmi_msghandler.c b/drivers/char/ipmi/ipmi_msghandler.c
> index 186f1fee7534..04f7622cb703 100644
> --- a/drivers/char/ipmi/ipmi_msghandler.c
> +++ b/drivers/char/ipmi/ipmi_msghandler.c
> @@ -5377,20 +5377,15 @@ static void send_panic_events(struct ipmi_smi *intf, char *str)
>  
>  	j = 0;
>  	while (*p) {
> -		int size = strlen(p);
> +		int size = strnlen(p, 11);
>  
> -		if (size > 11)
> -			size = 11;
>  		data[0] = 0;
>  		data[1] = 0;
>  		data[2] = 0xf0; /* OEM event without timestamp. */
>  		data[3] = intf->addrinfo[0].address;
>  		data[4] = j++; /* sequence # */
> -		/*
> -		 * Always give 11 bytes, so strncpy will fill
> -		 * it with zeroes for me.
> -		 */
> -		strncpy(data+5, p, 11);
> +
> +		strscpy_pad(data+5, p, 11);

This is incorrect, the destination should *not* be nil terminated if the
destination is full.  strncpy does exactly what is needed here.

A comment should be added here, this is not the first time this has been
brought up.

>  		p += size;
>  
>  		ipmi_panic_request_and_wait(intf, &addr, &msg);
> diff --git a/drivers/char/ipmi/ipmi_ssif.c b/drivers/char/ipmi/ipmi_ssif.c
> index 3b921c78ba08..edcb83765dce 100644
> --- a/drivers/char/ipmi/ipmi_ssif.c
> +++ b/drivers/char/ipmi/ipmi_ssif.c
> @@ -1940,7 +1940,7 @@ static int new_ssif_client(int addr, char *adapter_name,
>  		}
>  	}
>  
> -	strncpy(addr_info->binfo.type, DEVICE_NAME,
> +	strscpy(addr_info->binfo.type, DEVICE_NAME,
>  		sizeof(addr_info->binfo.type));

This one is good.

-corey

>  	addr_info->binfo.addr = addr;
>  	addr_info->binfo.platform_data = addr_info;
> 
> ---
> base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c
> change-id: 20230912-strncpy-drivers-char-ipmi-ipmi-dda47b3773fd
> 
> Best regards,
> --
> Justin Stitt <justinstitt@google.com>
>