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=-9.8 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=unavailable 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 1C401C388F7 for ; Mon, 9 Nov 2020 13:44:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D9DB0206B2 for ; Mon, 9 Nov 2020 13:44:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604929445; bh=jN5fmSJrOfr6qWUT73BoBnO6WztiLjL6wxVHT4LwTuU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=v5ZbywXlH1FDwoGWHqHfOMb9ZimobQKhfHRvuENfa08PV/OLw01TeTUnTeSmYtD+L v3y6VWqeJWLZjP0jdH1ofGtCR3auYnbhn5Cr0771rh7GXXndMomwbvM7XI+4547pEh l0aEaqUtM/5KxUiT0JrCWUWl6TcVs9GALz2iU/vk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730571AbgKINoE (ORCPT ); Mon, 9 Nov 2020 08:44:04 -0500 Received: from mail.kernel.org ([198.145.29.99]:53696 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730349AbgKIM70 (ORCPT ); Mon, 9 Nov 2020 07:59:26 -0500 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 E397E2076E; Mon, 9 Nov 2020 12:59:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604926765; bh=jN5fmSJrOfr6qWUT73BoBnO6WztiLjL6wxVHT4LwTuU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Osf+cdlz5gmDhycRQkzvfOSB8dzQj0ScLgwQbV+LG5trjxXcbKsF4vROgZX8nVYDC DML4Dpbodw7+6HrNcamv0AuYEdG7bXNY5s9er6x+WKnc0K0A5HQVS5gc0yZ/AgtU4w n3V7vFX9ryJfCmXB+48bjLHv0SM3ij0yRiG7eCQg= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Minh Yuan , Jiri Slaby Subject: [PATCH 4.4 43/86] vt: keyboard, extend func_buf_lock to readers Date: Mon, 9 Nov 2020 13:54:50 +0100 Message-Id: <20201109125022.918957917@linuxfoundation.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201109125020.852643676@linuxfoundation.org> References: <20201109125020.852643676@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Jiri Slaby commit 82e61c3909db51d91b9d3e2071557b6435018b80 upstream. Both read-side users of func_table/func_buf need locking. Without that, one can easily confuse the code by repeatedly setting altering strings like: while (1) for (a = 0; a < 2; a++) { struct kbsentry kbs = {}; strcpy((char *)kbs.kb_string, a ? ".\n" : "88888\n"); ioctl(fd, KDSKBSENT, &kbs); } When that program runs, one can get unexpected output by holding F1 (note the unxpected period on the last line): . 88888 .8888 So protect all accesses to 'func_table' (and func_buf) by preexisting 'func_buf_lock'. It is easy in 'k_fn' handler as 'puts_queue' is expected not to sleep. On the other hand, KDGKBSENT needs a local (atomic) copy of the string because copy_to_user can sleep. Use already allocated, but unused 'kbs->kb_string' for that purpose. Note that the program above needs at least CAP_SYS_TTY_CONFIG. This depends on the previous patch and on the func_buf_lock lock added in commit 46ca3f735f34 (tty/vt: fix write/write race in ioctl(KDSKBSENT) handler) in 5.2. Likely fixes CVE-2020-25656. Cc: Reported-by: Minh Yuan Signed-off-by: Jiri Slaby Link: https://lore.kernel.org/r/20201019085517.10176-2-jslaby@suse.cz Signed-off-by: Greg Kroah-Hartman --- drivers/tty/vt/keyboard.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) --- a/drivers/tty/vt/keyboard.c +++ b/drivers/tty/vt/keyboard.c @@ -712,8 +712,13 @@ static void k_fn(struct vc_data *vc, uns return; if ((unsigned)value < ARRAY_SIZE(func_table)) { + unsigned long flags; + + spin_lock_irqsave(&func_buf_lock, flags); if (func_table[value]) puts_queue(vc, func_table[value]); + spin_unlock_irqrestore(&func_buf_lock, flags); + } else pr_err("k_fn called with value=%d\n", value); } @@ -1969,7 +1974,7 @@ out: #undef s #undef v -/* FIXME: This one needs untangling and locking */ +/* FIXME: This one needs untangling */ int vt_do_kdgkb_ioctl(int cmd, struct kbsentry __user *user_kdgkb, int perm) { struct kbsentry *kbs; @@ -2001,10 +2006,14 @@ int vt_do_kdgkb_ioctl(int cmd, struct kb switch (cmd) { case KDGKBSENT: { /* size should have been a struct member */ - unsigned char *from = func_table[i] ? : ""; + ssize_t len = sizeof(user_kdgkb->kb_string); + + spin_lock_irqsave(&func_buf_lock, flags); + len = strlcpy(kbs->kb_string, func_table[i] ? : "", len); + spin_unlock_irqrestore(&func_buf_lock, flags); - ret = copy_to_user(user_kdgkb->kb_string, from, - strlen(from) + 1) ? -EFAULT : 0; + ret = copy_to_user(user_kdgkb->kb_string, kbs->kb_string, + len + 1) ? -EFAULT : 0; goto reterr; }