Subject: Re: strncpy optimalisation? (lib/string.c)
From: Bernd Petrovitsch <bernd@firmix.at>
To: Folkert van Heusden <folkert@vanheusden.com>
Cc: Mitchell Blank Jr <mitch@sfgoth.com>, Willy Tarreau <w@1wt.eu>,
       linux-kernel@vger.kernel.org, kernel-janitors@lists.osdl.org
In-Reply-To: <20061210213925.GE30197@vanheusden.com>
References: <20061210205230.GB30197@vanheusden.com>
	 <20061210210614.GD24090@1wt.eu> <20061210214934.GC47959@gaz.sfgoth.com>
	 <20061210213925.GE30197@vanheusden.com>
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Organization: Firmix Software GmbH
Date: Mon, 11 Dec 2006 00:28:45 +0100
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On Sun, 2006-12-10 at 22:39 +0100, Folkert van Heusden wrote:
> > > Original code completely pads the destination with zeroes,
> > > while yours only adds the last zero. Your code does what
> > > strncpy() is said to do, but maybe there's a particular
> > > reason for it to behave differently in the kernel
> > No, the kernel's strncpy() behaves the same as the one in libc.  Run
> > "man strncpy" if you don't believe me.
> > In the common case where you just want to copy a string and avoid
> > overflow use strlcpy() instead
> 
> Oops you're right! Maybe someone should take a look if the strncpy's
> should be replaced by strlcpy's then because it is (ought to be) faster.

The last time some folks did this (quite automatically) ended in newly
introduced bugs leaking old/stale data from kernel top user space. Alan
Cox went over it (again) and fixed those broken "optimizations".

So whoever wants to do this, look for such issues too.

	Bernd
-- 
Firmix Software GmbH                   http://www.firmix.at/
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