linux-kernel - Re: [PATCH] hda_hwdep: Fix possible buffer overflow

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Message-Id: <201110261515.25189.alexander.stein@systec-electronic.com>
Date:	Wed, 26 Oct 2011 15:15:24 +0200
From:	Alexander Stein <alexander.stein@...tec-electronic.com>
To:	Takashi Iwai <tiwai@...e.de>
Cc:	Jaroslav Kysela <perex@...ex.cz>, alsa-devel@...a-project.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hda_hwdep: Fix possible buffer overflow

Hello,

On Wednesday 26 October 2011 14:58:43 Takashi Iwai wrote:
> At Wed, 26 Oct 2011 09:48:12 +0200,
> 
> Alexander Stein wrote:
> > If a line in the firmware file is larger than the given buffer size (and
> > so the firmware file size), size is set to a value larger than the actual
> > buffer size. This results in an overflow in the buffer passed.
> > Fix this by copying only up to 127 chars per line.
> 
> Actually this check should have been
> 
> 	if (size > fw->size)
> 		size = fw->size;
> 
> Otherwise it doesn't make sense.
> If the change is OK, could you resend the patch with it?

IMO this check isn't even needed. This case should be catched by this check

   for (len = 0; len < fw->size; len++) {

already.
Opinions?

Alexader

> > Signed-off-by: Alexander Stein <alexander.stein@...tec-electronic.com>
> > ---
> > 
> >  sound/pci/hda/hda_hwdep.c |    6 +++---
> >  1 files changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/sound/pci/hda/hda_hwdep.c b/sound/pci/hda/hda_hwdep.c
> > index bf3ced5..61da08d 100644
> > --- a/sound/pci/hda/hda_hwdep.c
> > +++ b/sound/pci/hda/hda_hwdep.c
> > @@ -745,6 +745,7 @@ static int parse_line_mode(char *buf, struct hda_bus
> > *bus)
> > 
> >   * if successfully copied a line
> >   *
> >   * the spaces at the beginning and the end of the line are stripped
> > 
> > + * lines read are clamped to 127 chars
> > 
> >   */
> >  
> >  static int get_line_from_fw(char *buf, int size, struct firmware *fw)
> >  {
> > 
> > @@ -756,8 +757,6 @@ static int get_line_from_fw(char *buf, int size,
> > struct firmware *fw)
> > 
> >  	}
> >  	if (!fw->size)
> >  	
> >  		return 0;
> > 
> > -	if (size < fw->size)
> > -		size = fw->size;
> > 
> >  	for (len = 0; len < fw->size; len++) {
> >  	
> >  		if (!*p)
> > 
> > @@ -768,7 +767,8 @@ static int get_line_from_fw(char *buf, int size,
> > struct firmware *fw)
> > 
> >  			break;
> >  		
> >  		}
> >  		if (len < size)
> > 
> > -			*buf++ = *p++;
> > +			*buf++ = *p;
> > +		p++;
> > 
> >  	}
> >  	*buf = 0;
> >  	fw->size -= len;
--
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