Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759819AbZDWVrt (ORCPT ); Thu, 23 Apr 2009 17:47:49 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753773AbZDWVrl (ORCPT ); Thu, 23 Apr 2009 17:47:41 -0400 Received: from smtp4.welho.com ([213.243.153.38]:37909 "EHLO smtp4.welho.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752675AbZDWVrk (ORCPT ); Thu, 23 Apr 2009 17:47:40 -0400 Date: Fri, 24 Apr 2009 00:47:38 +0300 From: Ville =?iso-8859-1?Q?Syrj=E4l=E4?= To: Andrew Morton Cc: Roel Kluin , linux-fbdev-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org, adaplas@gmail.com Subject: Re: [Linux-fbdev-devel] fbcmap: non working tests on unsigned cmap->start Message-ID: <20090423214738.GF7134@sci.fi> Mail-Followup-To: Andrew Morton , Roel Kluin , linux-fbdev-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org, adaplas@gmail.com References: <49EDD799.8060607@gmail.com> <20090423134110.51ea8df2.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20090423134110.51ea8df2.akpm@linux-foundation.org> User-Agent: Mutt/1.5.16 (2007-06-09) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2264 Lines: 64 On Thu, Apr 23, 2009 at 01:41:10PM -0700, Andrew Morton wrote: > On Tue, 21 Apr 2009 16:26:33 +0200 > Roel Kluin wrote: > > > vi include/linux/fb.h +478 > > > > Note that struct fb_cmap_user cmap->start in fb_set_user_cmap() is unsigned. > > Should there maybe be a test: > > > > if (cmap->start > MAX || ...) > > > > (and what should MAX be then?) > > > > Otherwise you may want to apply the cleanup patch below > > > > Roel > > ------------------------------>8-------------8<--------------------------------- > > Remove redundant tests on unsigned > > > > Signed-off-by: Roel Kluin > > --- > > diff --git a/drivers/video/fbcmap.c b/drivers/video/fbcmap.c > > index f53b9f1..958bf4e 100644 > > --- a/drivers/video/fbcmap.c > > +++ b/drivers/video/fbcmap.c > > @@ -266,8 +266,7 @@ int fb_set_user_cmap(struct fb_cmap_user *cmap, struct fb_info *info) > > rc = -ENODEV; > > goto out; > > } > > - if (cmap->start < 0 || (!info->fbops->fb_setcolreg && > > - !info->fbops->fb_setcmap)) { > > + if (!info->fbops->fb_setcolreg && !info->fbops->fb_setcmap) { > > rc = -EINVAL; > > goto out1; > > } > > argh. > > - Perhaps userspace can kill the kernel by sending a "negative" > `start'. Removing the test will make it even less likely that we'll > fix this bug. Shouldn't happen. 'start' is used as the starting index for the hardware palette, 'start+len-1' is the last index. All drivers should already check the passed values since the maximum index depends on the display mode. And I suppose the worst thing that could happen if the driver fails to check the values would be incorrect colors. > - If this bug doesn't exist, and there _is_ userspace which is > legitimately sending in "negative" values of `start' (unlikely?) then > we will break userspace if we fix this comparison. The comparison will always be false since 'start' is unsigned so how would anything break? -- Ville Syrj?l? syrjala@sci.fi http://www.sci.fi/~syrjala/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/