netdev - Re: [patch] isdn: fix information leak

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Message-ID: <AANLkTikGNr8aVV7Rryq_dvSuYjUbEo_gRDLW3d49YwF-@mail.gmail.com>
Date:	Thu, 5 Aug 2010 21:18:00 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Dan Carpenter <error27@...il.com>
Cc:	Karsten Keil <isdn@...ux-pingi.de>, netdev@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [patch] isdn: fix information leak

On Thu, Aug 5, 2010 at 7:37 PM, Dan Carpenter <error27@...il.com> wrote:
>
> Both strncpy() and strlcpy() take a limitter.  The difference is that
> strlcpy() always takes on a terminator and strncpy() only adds a
> terminator if there is space.
>
> strlcpy() is a BSD function that never caught on in Linux.  The glibc
> maintainers think that if you accidentally chop off the last part of a
> word that makes you an idiot.  They think you should known the length of
> your data at all times and use memcpy() or a proper string library.
>
> I prefer strlcpy() to strncpy().  Some people do stuff like:
>        strncpy(bar, foo, n);
>        bar[n] = '\0';
> You have to read through the code to find if n is "sizeof(bar)" or
> "sizeof(bar) - 1".  Which is a pain in the arse.  strlcpy() is explicit
> and it's just one line of code instead of two.
>
> The other tricky thing you should remember about strncpy() is that the
> posix version writes NUL chars from the end of the string to the
> limitter but the kernel version only copies one NUL character.
>

You should spend some time on reading the source code of strlcpy() and
strncpy().

the example use of them is:

char dst[24];
char *src = "test";

strncpy(dst, src, sizeof(dst) - 1);
strlcpy(dst, src, sizeof(dst));

both of them don't need to zero dst, and they don't need to pad zero
at then end of the dst.

-- 
Regards,
Changli Gao(xiaosuo@...il.com)
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