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From: Borislav Petkov <bp@alien8.de>
To: Len Baker <len.baker@gmx.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>,
	Tony Luck <tony.luck@intel.com>,
	James Morse <james.morse@arm.com>,
	Robert Richter <rric@kernel.org>, Joe Perches <joe@perches.com>,
	David Laight <David.Laight@aculab.com>,
	Kees Cook <keescook@chromium.org>,
	linux-hardening@vger.kernel.org, linux-edac@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4] EDAC/mc: Prefer strscpy over strcpy
Date: Tue, 24 Aug 2021 20:26:10 +0200	[thread overview]
Message-ID: <YSU5wp/ZpsXuDgmu@zn.tnic> (raw)
In-Reply-To: <20210824090338.GB7999@titan>

On Tue, Aug 24, 2021 at 12:28:07PM +0200, Len Baker wrote:
> This is a task of the KSPP [1] and the main reason is to clean up the
> proliferation of str*cpy functions in the kernel.

That I understood - you prominently explain where the patches stem from.

What I can't parse is that formulation "previous step". What previous
step do you mean?

> Yes, you are right. The same discussion happened in the v3 review [2] and
> I agree with the reasons that Robert Richter exposed. Using the strlen()
> implementation it is not necessary to check the return code of strcpy and
> we can assume a silent truncation.
> 
> [2] https://lore.kernel.org/linux-hardening/YRN+8u59lJ6MWsOL@rric.localdomain/

Ok, looking at the asm, gcc is actually smart enough not to call
strlen() twice on the same buffer.

But then there's this in the strscpy() kernel-doc comment:

"The destination buffer is always NUL terminated, unless it's
zero-sized."

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;

so if p ends up pointing to something which is *not* '\0', strlen() will
go off into the weeds.

So I don't care if it doesn't look just as nice - it better be correct
in all cases first.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

  reply	other threads:[~2021-08-24 18:25 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-14  7:55 Len Baker
2021-08-23 17:30 ` Borislav Petkov
2021-08-24 10:28   ` Len Baker
2021-08-24 18:26     ` Borislav Petkov [this message]
2021-08-24 19:05       ` Joe Perches
2021-08-25  8:48       ` David Laight
2021-08-27 17:36       ` Len Baker
2021-08-27 17:54         ` Borislav Petkov
2021-08-27 19:08           ` Joe Perches
2021-08-29 16:14           ` Len Baker

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