From patchwork Tue Sep 1 15:10:34 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 264703 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=-10.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 8CECDC433E2 for ; Tue, 1 Sep 2020 15:43:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4BAA62064B for ; Tue, 1 Sep 2020 15:43:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598975030; bh=yV4NorN4UzjU8UKxeQwkwOTaHZr/jd/fGwxrs6294rk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=oDwEaIajlZ7LIqaCMb3oIqzm4O1pvMGQp433AeDwUAiUsEfeZ5Mr7Dmj4CrGBDD3U JVlSKm2TkfSI5eaVIpFyYfVBJfwSbBQTETyriZO86lrk5+zrdQvs4b1qA9k2lU0e0g qnCoT2va9V1lz+A6eezzxTadpQHy3I6FwRyDsm1M= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731670AbgIAPnp (ORCPT ); Tue, 1 Sep 2020 11:43:45 -0400 Received: from mail.kernel.org ([198.145.29.99]:58128 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731688AbgIAPno (ORCPT ); Tue, 1 Sep 2020 11:43:44 -0400 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C18F1206EF; Tue, 1 Sep 2020 15:43:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598975023; bh=yV4NorN4UzjU8UKxeQwkwOTaHZr/jd/fGwxrs6294rk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=TxX02Fs2GIarxNuNxuiorNIDR0eYYtwxRzI3KOPuTPTjj88YaKbt06viXophaSucQ aODBN5A+pjFwT4VySEPb2OQVIbrRe4m73i6QhZqSOIRoraoUaq4AWAB0mEHm/Jx3fa utovpcfJ0DgyfB+/ORpy+aoL+d9G5jylBk1Wlals= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, syzbot , Tetsuo Handa Subject: [PATCH 5.8 178/255] vt: defer kfree() of vc_screenbuf in vc_do_resize() Date: Tue, 1 Sep 2020 17:10:34 +0200 Message-Id: <20200901151009.217388144@linuxfoundation.org> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20200901151000.800754757@linuxfoundation.org> References: <20200901151000.800754757@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Tetsuo Handa commit f8d1653daec02315e06d30246cff4af72e76e54e upstream. syzbot is reporting UAF bug in set_origin() from vc_do_resize() [1], for vc_do_resize() calls kfree(vc->vc_screenbuf) before calling set_origin(). Unfortunately, in set_origin(), vc->vc_sw->con_set_origin() might access vc->vc_pos when scroll is involved in order to manipulate cursor, but vc->vc_pos refers already released vc->vc_screenbuf until vc->vc_pos gets updated based on the result of vc->vc_sw->con_set_origin(). Preserving old buffer and tolerating outdated vc members until set_origin() completes would be easier than preventing vc->vc_sw->con_set_origin() from accessing outdated vc members. [1] https://syzkaller.appspot.com/bug?id=6649da2081e2ebdc65c0642c214b27fe91099db3 Reported-by: syzbot Signed-off-by: Tetsuo Handa Cc: stable Link: https://lore.kernel.org/r/1596034621-4714-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp Signed-off-by: Greg Kroah-Hartman --- drivers/tty/vt/vt.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) --- a/drivers/tty/vt/vt.c +++ b/drivers/tty/vt/vt.c @@ -1196,7 +1196,7 @@ static int vc_do_resize(struct tty_struc unsigned int old_rows, old_row_size, first_copied_row; unsigned int new_cols, new_rows, new_row_size, new_screen_size; unsigned int user; - unsigned short *newscreen; + unsigned short *oldscreen, *newscreen; struct uni_screen *new_uniscr = NULL; WARN_CONSOLE_UNLOCKED(); @@ -1294,10 +1294,11 @@ static int vc_do_resize(struct tty_struc if (new_scr_end > new_origin) scr_memsetw((void *)new_origin, vc->vc_video_erase_char, new_scr_end - new_origin); - kfree(vc->vc_screenbuf); + oldscreen = vc->vc_screenbuf; vc->vc_screenbuf = newscreen; vc->vc_screenbuf_size = new_screen_size; set_origin(vc); + kfree(oldscreen); /* do part of a reset_terminal() */ vc->vc_top = 0;