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

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Date:   Wed, 25 Aug 2021 08:48:03 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Borislav Petkov' <bp@...en8.de>, 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>,
        Kees Cook <keescook@...omium.org>,
        "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v4] EDAC/mc: Prefer strscpy over strcpy

From: Borislav Petkov
> Sent: 24 August 2021 19:26
..
> so looking at the code, we're merrily decrementing len but nothing's
> checking whether len can become 0. Because if it does, strscpy() will
> do:
> 
> 	if (count == 0 || WARN_ON_ONCE(count > INT_MAX))
> 		return -E2BIG;

That -E2BIG is going to break something.
It means that you always have to do an error check whenever
you use the return value of strscpy().

Anything that does:
	offset += strscpy(...)
is broken.

It really wasn't a good idea for reporting 'truncated'.

	David

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