linux-kernel - Re: [patch v2] cx231xx: card->driver "Conexant cx231xx Audio" too long

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Date:	Mon, 22 Mar 2010 17:04:55 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	Joe Perches <joe@...ches.com>
Cc:	Dan Carpenter <error27@...il.com>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	Srinivasa Deevi <srinivasa.deevi@...exant.com>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [patch v2] cx231xx: card->driver "Conexant cx231xx Audio" too long

At Mon, 22 Mar 2010 08:43:47 -0700,
Joe Perches wrote:
> 
> On Mon, 2010-03-22 at 18:39 +0300, Dan Carpenter wrote:
> > card->driver is 15 characters and a NULL, the original code could 
> > cause a buffer overflow.
> 
> > In version 2, I used a better name that Takashi Iwai suggested.
> 
> Perhaps it's better to use strncpy as well.

strlcpy() would be safer :)

But, in such a case, we want rather that the error is notified at
build time.

Maybe a macro like below would be helpful to catch such bugs?

#define COPY_STRING(buf, src)						\
	do {								\
		if (__builtin_constant_p(src))				\
			BUILD_BUG_ON(strlen(src) >= sizeof(buf));	\
		strcpy(buf, src);					\
	} while (0)

and used like:

struct foo {
	char foo[5];
} x;

COPY_STRING(x.foo, "OK"); // OK
COPY_STRING(x.foo, "1234567890"); // NG


Takashi
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