linux-hardening - Re: [PATCH v4] EDAC/mc: Prefer strscpy over strcpy

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Date:   Mon, 23 Aug 2021 19:30:34 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Len Baker <len.baker@....com>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        James Morse <james.morse@....com>,
        Robert Richter <rric@...nel.org>,
        Joe Perches <joe@...ches.com>,
        David Laight <David.Laight@...lab.com>,
        Kees Cook <keescook@...omium.org>,
        linux-hardening@...r.kernel.org, linux-edac@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] EDAC/mc: Prefer strscpy over strcpy

On Sat, Aug 14, 2021 at 09:55:27AM +0200, Len Baker wrote:
> strcpy() performs no bounds checking on the destination buffer. This
> could result in linear overflows beyond the end of the buffer, leading
> to all kinds of misbehaviors. The safe replacement is strscpy().
> 
> This is a previous step in the path to remove the strcpy() function

"previous step"?

> entirely from the kernel.
> 
> Signed-off-by: Len Baker <len.baker@....com>

...

> diff --git a/drivers/edac/edac_mc.c b/drivers/edac/edac_mc.c
> index f6d462d0be2d..7aea6c502316 100644
> --- a/drivers/edac/edac_mc.c
> +++ b/drivers/edac/edac_mc.c
> @@ -1032,6 +1032,7 @@ void edac_mc_handle_error(const enum hw_event_mc_err_type type,
>  	int i, n_labels = 0;
>  	struct edac_raw_error_desc *e = &mci->error_desc;
>  	bool any_memory = true;
> +	size_t len;
> 
>  	edac_dbg(3, "MC%d\n", mci->mc_idx);
> 
> @@ -1086,6 +1087,7 @@ void edac_mc_handle_error(const enum hw_event_mc_err_type type,
>  	 */
>  	p = e->label;
>  	*p = '\0';
> +	len = sizeof(e->label);
> 
>  	mci_for_each_dimm(mci, dimm) {
>  		if (top_layer >= 0 && top_layer != dimm->location[0])
> @@ -1114,10 +1116,12 @@ void edac_mc_handle_error(const enum hw_event_mc_err_type type,
>  			*p = '\0';
>  		} else {
>  			if (p != e->label) {
> -				strcpy(p, OTHER_LABEL);
> -				p += strlen(OTHER_LABEL);
> +				strscpy(p, OTHER_LABEL, len);

Hm, maybe I'm missing something but looking at that strscpy()
definition, why aren't you doing:

				num = strscpy(p, OTHER_LABEL, len);
				if (num < 0)
					/* just in case */
					break;

				len -= num;
				p   += num;

since that function supposedly returns the number of chars copied.

> +				len -= strlen(p);
> +				p += strlen(p);
>  			}
> -			strcpy(p, dimm->label);
> +			strscpy(p, dimm->label, len);
> +			len -= strlen(p);
>  			p += strlen(p);

Ditto.

Thx.

-- 
Regards/Gruss,
    Boris.

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