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

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Date:	Thu, 18 Jul 2013 14:50:52 +0800
From:	Chen Gang <gang.chen@...anux.com>
To:	George Spelvin <linux@...izon.com>
CC:	andrei.emeltchenko@...el.com, andriy.shevchenko@...ux.intel.com,
	jkosina@...e.cz, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] lib/vsprintf.c: fix the incorrect return value of vsnprintf()

On 07/18/2013 02:42 PM, George Spelvin 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.
> NAK.  This is the documented (by both the function itself and the
> ANSI/ISO C standard) and desired return value: the number of bytes that
> *would* have been in the output string if the buffer were large enough.
> In particular, it is common to do:
> 
> size = vsnprintf(NULL, 0, fmt, args) + 1;
> p = malloc(size, GFP_KERNEL);
> vsnprintf(p, size, fmt, args);
> 

OK, it is my fault, thank you very much.

> You want vscnprintf.  If you have a caller that needs the *actual* number of
> bytes written, use that.
> 
> 

Yeah, my another patch need use vscnprintf() instead of vsnprintf(),
thanks again.


Thanks.
-- 
Chen Gang
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