linux-hardening - Re: [PATCH v5] EDAC/mc: Prefer strscpy or scnprintf over strcpy

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Date:   Fri, 3 Sep 2021 16:21:46 +0200
From:   Len Baker <len.baker@....com>
To:     Joe Perches <joe@...ches.com>
Cc:     Len Baker <len.baker@....com>, Borislav Petkov <bp@...en8.de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        James Morse <james.morse@....com>,
        Robert Richter <rric@...nel.org>,
        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 v5] EDAC/mc: Prefer strscpy or scnprintf over strcpy

Hi,

On Sun, Aug 29, 2021 at 09:38:37AM -0700, Joe Perches wrote:
> On Sun, 2021-08-29 at 18:15 +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() [1].
> >
> > However, to simplify and clarify the code, to concatenate labels use
> > the scnprintf() function. This way it is not necessary to check the
> > return value of strscpy (-E2BIG if the parameter count is 0 or the src
> > was truncated) since the scnprintf returns always the number of chars
> > written into the buffer. This function returns always a nul-terminated
> > string even if it needs to be truncated.
> []
> > diff --git a/drivers/edac/edac_mc.c b/drivers/edac/edac_mc.c
> []
> > @@ -1113,12 +1116,11 @@ void edac_mc_handle_error(const enum hw_event_mc_err_type type,
> >  			p = e->label;
> >  			*p = '\0';
> >  		} else {
> > -			if (p != e->label) {
> > -				strcpy(p, OTHER_LABEL);
> > -				p += strlen(OTHER_LABEL);
> > -			}
> > -			strcpy(p, dimm->label);
> > -			p += strlen(p);
> > +			const char *or = (p != e->label) ? OTHER_LABEL : "";
> > +
> > +			n = scnprintf(p, len, "%s%s", or, dimm->label);
> > +			len -= n;
> > +			p += n;
>
> A very common and intelligible mechanism for this is:
>
> 	const char *prefix = "";
> 	int n = 0;
> 	...
> 			n += scnprintf(e->label + n, sizeof(e->label) - n,
> 				       "%s%s", prefix, dimm->label);
> 			prefix = " or ";
>
Ok, I will send a new version using this common mechanism. Thanks for the
advise.

Regards,
Len