linux-kernel - Re: [patch] tracing: off by one in __trace_array

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Message-ID: <20141126092706.5d4038d4@gandalf.local.home>
Date:	Wed, 26 Nov 2014 09:27:06 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Dan Carpenter <dan.carpenter@...cle.com>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [patch] tracing: off by one in __trace_array_vprintk()

On Wed, 26 Nov 2014 17:06:21 +0300
Dan Carpenter <dan.carpenter@...cle.com> wrote:

> This check says "goto out;" if we had to truncate the string.
> 
> The "tbuffer" buffer has TRACE_BUF_SIZE bytes.  The vsnprintf() function
> returns the number of characters (not counting the NUL char) which would
> have been printed if there were space.  If we we tried to print
> TRACE_BUF_SIZE characters, the last character would have been truncated
> to make space for the NUL character so we should "goto out;".
> 

Oh, and the NUL character is never copied. We copy the string into the
buffer with:

	memcpy(&entry->buf, tbuffer, len);

Where len does not include NUL, and why we add it ourselves.

-- Steve
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