From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 068DFC48BE8 for ; Tue, 15 Jun 2021 13:28:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E6C1261474 for ; Tue, 15 Jun 2021 13:28:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231185AbhFONaS (ORCPT ); Tue, 15 Jun 2021 09:30:18 -0400 Received: from mail.kernel.org ([198.145.29.99]:35642 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231453AbhFONaI (ORCPT ); Tue, 15 Jun 2021 09:30:08 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id C6CA261468; Tue, 15 Jun 2021 13:28:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1623763684; bh=s4DCRr6gd8QdC/cIRhXmf9yOcNT5lHnTgdw2ssrVcfc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=eS3N8PXWeiD9ris3hzIoJuLWn2NGjTdShLrljniwaPU6/GCsQx081P3i9GY/GGoi0 1QZbWqrKpygg5tCF3Jxy2C6o6uSt6t2e0Ijc+IQ2MNOKlCurBgbGtnjdcpVouHaw2o srePOQA4J+SyUl/UYh5XamQCK8rigmbn50YQdt1U= Date: Tue, 15 Jun 2021 15:28:01 +0200 From: Greg KH To: Igor Matheus Andrade Torrente Cc: jirislaby@kernel.org, linux-kernel@vger.kernel.org, syzbot+858dc7a2f7ef07c2c219@syzkaller.appspotmail.com Subject: Re: [PATCH v2] tty: Fix out-of-bound vmalloc access in imageblit Message-ID: References: <20210614131859.9511-1-igormtorrente@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210614131859.9511-1-igormtorrente@gmail.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 14, 2021 at 10:18:59AM -0300, Igor Matheus Andrade Torrente wrote: > This issue happens when a userspace program does an ioctl > FBIOPUT_VSCREENINFO passing the fb_var_screeninfo struct > containing only the fields xres, yres, and bits_per_pixel > with values. > > If this struct is the same as the previous ioctl, the > vc_resize() detects it and doesn't call the resize_screen(), > leaving the fb_var_screeninfo incomplete. And this leads to > the updatescrollmode() calculates a wrong value to > fbcon_display->vrows, which makes the real_y() return a > wrong value of y, and that value, eventually, causes > the imageblit to access an out-of-bound address value. > > To solve this issue I made the resize_screen() be called > even if the screen does not need any resizing, so it will > "fix and fill" the fb_var_screeninfo independently. > > Reported-and-tested-by: syzbot+858dc7a2f7ef07c2c219@syzkaller.appspotmail.com > Signed-off-by: Igor Matheus Andrade Torrente > --- > v2: It Tries to avoid the problem found by Greg in the previous > patch. > --- > drivers/tty/vt/vt.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c > index fa1548d4f94b..e522f9b249e5 100644 > --- a/drivers/tty/vt/vt.c > +++ b/drivers/tty/vt/vt.c > @@ -1219,8 +1219,10 @@ static int vc_do_resize(struct tty_struct *tty, struct vc_data *vc, > new_row_size = new_cols << 1; > new_screen_size = new_row_size * new_rows; > > - if (new_cols == vc->vc_cols && new_rows == vc->vc_rows) > - return 0; > + if (new_cols == vc->vc_cols && new_rows == vc->vc_rows) { > + err = resize_screen(vc, new_cols, new_rows, user); > + return err; Shouldn't this just be a single line change to: return resize_screen(vc, new_cols, new_rows, user); ? But this also should get a big comment, as it looks odd that if the size isn't changing, why this function should be called at all. At first glance at just the code, this looks wrong, so please document this really well here. thanks, greg k-h