From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: fbcmap: non working tests on unsigned cmap->start Date: Thu, 23 Apr 2009 13:41:10 -0700 Message-ID: <20090423134110.51ea8df2.akpm@linux-foundation.org> References: <49EDD799.8060607@gmail.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <49EDD799.8060607@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Roel Kluin Cc: adaplas@gmail.com, linux-fbdev-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org 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. - 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. IOW, I don't have enough knowledge about this code to be able to know what to do.