linux-kernel - Re: [PATCH] tty/metag_da: initialize number

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Date:	Sat, 6 Feb 2016 23:41:09 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Colin Ian King <colin.king@...onical.com>
Cc:	James Hogan <james.hogan@...tec.com>, Jiri Slaby <jslaby@...e.com>,
	linux-metag@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tty/metag_da: initialize number_written to zero

On Thu, Jan 28, 2016 at 06:48:17PM +0000, Colin Ian King wrote:
> On 27/01/16 11:42, James Hogan wrote:
> > Hi Colin,
> > 
> > On Tue, Jan 26, 2016 at 11:37:25PM +0000, Colin King wrote:
> >> From: Colin Ian King <colin.king@...onical.com>
> >>
> >> number_written is not initialized, so it can be any value. In the
> >> case where dport->xmit_cnt is zero, number_written is not set
> >> and subsequent accesses to it will be reading a garbage value.
> > 
> > the only subsequent accesses when dport->xmit_cnt == 0 are:
> > 
> > 	/* if we've made more data available, wake up tty */
> > 	if (count && number_written) {
> > 
> > and:
> > 
> > 	/* did the write fail? */
> > 	return count && !number_written;
> > 
> > but dport->xmit_cnt == 0 implies count == 0, so number_written shouldn
> 't
> > be used, and both will evaluate to false regardless of the uninitialis
> ed
> > value, so it looks fine as it is to me.
> > 
> > Is this tripping up some static analysis tool or something?
> 
> It was found using cppcheck, namely:
> 
> [drivers/tty/metag_da.c:269]: (error) Uninitialized variable: number_wri
> tten

Please fix the broken tool, don't paper over it by doing unnecessary
work in the kernel.

thanks,

greg k-h