linux-kernel - Re: [PATCH 1/3] tools/hv: Fix for long file names from readdir

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Date:	Thu, 17 Jan 2013 10:41:06 -0800
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Ben Hutchings <ben@...adent.org.uk>
Cc:	Tomas Hozza <thozza@...hat.com>, olaf@...fle.de,
	jasowang@...hat.com, linux-kernel@...r.kernel.org,
	apw@...onical.com, devel@...uxdriverproject.org
Subject: Re: [PATCH 1/3] tools/hv: Fix for long file names from readdir

On Tue, Dec 18, 2012 at 12:38:03PM +0000, Ben Hutchings wrote:
> On Tue, 2012-12-18 at 03:06 -0500, Tomas Hozza wrote:
> > ----- Original Message -----
> > > > This is just for sanity. The value PATH_MAX was chosen after
> > > > discussion
> > > > with K. Y. Srinivasan and Olaf Hering instead of some "magic"
> > > > number like
> > > > 256 or 512.
> > > 
> > > PATH_MAX is a magic name.
> > 
> > It is defined in "limits.h". I would welcome some more constructive
> > argumentation and critics.
> 
> It still bears no relation to any actual limit in the C library or Linux
> kernel.  So it's no more valid than the previous number.
> 
> In the current context we're enumerating /sys/class/net and we know that
> all the interface names in there are limited to IFNAMSIZ-1 = 15 (there
> is also potentially "bonding_masters").  The longest path name we need
> to use is definitely much shorter than even 256 bytes.
> 
> > > > > Using snprintf() is a good idea, but you need to check the return
> > > > > value and handle the truncation case somehow.
> > > > 
> > > > By using PATH_MAX sized buffer there is no need for handling the
> > > > truncation
> > > > case.
> > >  
> > > You are claiming two contradictory things: sprintf() may overrun the
> > > buffer, so we need the length check provided by snprintf(), but there
> > > is no need to check for truncation because we know the length is
> > > sufficient.
> > 
> > So what do you propose? How should it be solved?
> 
> 	if (snprintf(dev_id, sizeof(dev_id), ...) >= sizeof(dev_id))
> 		continue;
> 
> Possibly logging a warning.

I agree, I'm dropping this patch from my to-apply queue.

greg k-h
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