linux-kernel - Re: [PATCH] lib/vsprintf.c: fix the incorrect return value of vsnprintf()

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Message-ID: <20130718064953.GX4165@ZenIV.linux.org.uk>
Date:	Thu, 18 Jul 2013 07:49:53 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Chen Gang <gang.chen@...anux.com>
Cc:	linux@...izon.com, Jiri Kosina <jkosina@...e.cz>,
	andriy.shevchenko@...ux.intel.com, andrei.emeltchenko@...el.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] lib/vsprintf.c: fix the incorrect return value of
 vsnprintf()

On Thu, Jul 18, 2013 at 02:28:49PM +0800, Chen Gang wrote:
> When "str >= end", necessary to reset 'str' to "end - 1", or the return
> value will be larger than the real one, the callers which depend on the
> return value, may cause memory overflow.

You do realize that snprintf(s, 1, "abc") should return 3, not 1?  The
goal off snprintf() is _not_ just to truncate the output; return value
tells how much should the buffer had been to fit the whole thing.
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