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=-5.2 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FSL_HELO_FAKE,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT 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 0E48AC43441 for ; Wed, 14 Nov 2018 22:28:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C824020868 for ; Wed, 14 Nov 2018 22:28:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="vyD6ubFw" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C824020868 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389439AbeKOIdt (ORCPT ); Thu, 15 Nov 2018 03:33:49 -0500 Received: from mail.kernel.org ([198.145.29.99]:39386 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2388782AbeKOIci (ORCPT ); Thu, 15 Nov 2018 03:32:38 -0500 Received: from gmail.com (unknown [104.132.1.85]) (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 B13382175B; Wed, 14 Nov 2018 21:54:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1542232477; bh=GgKyYMrZlbrZnXx2A/eOE1QtMQFOf0REK5vqRqD3XNU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=vyD6ubFwCqtR8Tfq9aOrb+wjz38bgoiIXmrW1zUtv4zy/V37qmNMCjic+nRaOjPTc baRoJ/KJlX3PnkIYn5aYoJhh5xDw4lQeF4+kxvW3LMUXaAyG9uxj/klHV2qOfIO4uZ YPZ6+5PNmzDUkcazLGj1EAGmU71dWWfi+uMZFEr8= Date: Wed, 14 Nov 2018 13:54:35 -0800 From: Eric Biggers To: Jann Horn Cc: dh.herrmann@googlemail.com, Jiri Kosina , benjamin.tissoires@redhat.com, linux-input@vger.kernel.org, kernel list , syzkaller-bugs@googlegroups.com, Dmitry Vyukov , dtor@google.com, syzbot+72473edc9bf4eb1c6556@syzkaller.appspotmail.com, stable@vger.kernel.org, Andy Lutomirski Subject: Re: [PATCH] HID: uhid: prevent uhid_char_write() under KERNEL_DS Message-ID: <20181114215434.GB87768@gmail.com> References: <20181114171447.GA87768@gmail.com> <20181114180217.195917-1-ebiggers@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 14, 2018 at 07:18:39PM +0100, 'Jann Horn' via syzkaller-bugs wrote: > +cc Andy > > On Wed, Nov 14, 2018 at 7:03 PM Eric Biggers wrote: > > When a UHID_CREATE command is written to the uhid char device, a > > copy_from_user() is done from a user pointer embedded in the command. > > When the address limit is KERNEL_DS, e.g. as is the case during > > sendfile(), this can read from kernel memory. Therefore, UHID_CREATE > > must not be allowed in this case. > > > > For consistency and to make sure all current and future uhid commands > > are covered, apply the restriction to uhid_char_write() as a whole > > rather than to UHID_CREATE specifically. > > > > Thanks to Dmitry Vyukov for adding uhid definitions to syzkaller and to > > Jann Horn for commit 9da3f2b740544 ("x86/fault: BUG() when uaccess > > helpers fault on kernel addresses"), allowing this bug to be found. > > > > Reported-by: syzbot+72473edc9bf4eb1c6556@syzkaller.appspotmail.com > > Wheeeee, it found something! :) > > > Fixes: d365c6cfd337 ("HID: uhid: add UHID_CREATE and UHID_DESTROY events") > > Cc: # v3.6+ > > Cc: Jann Horn > > Signed-off-by: Eric Biggers > > --- > > drivers/hid/uhid.c | 6 ++++++ > > 1 file changed, 6 insertions(+) > > > > diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c > > index 3c55073136064..e94c5e248b56e 100644 > > --- a/drivers/hid/uhid.c > > +++ b/drivers/hid/uhid.c > > @@ -705,6 +705,12 @@ static ssize_t uhid_char_write(struct file *file, const char __user *buffer, > > int ret; > > size_t len; > > > > + if (uaccess_kernel()) { /* payload may contain a __user pointer */ > > + pr_err_once("%s: process %d (%s) called from kernel context, this is not allowed.\n", > > + __func__, task_tgid_vnr(current), current->comm); > > + return -EACCES; > > + } > > If this file can conceivably be opened by a process that doesn't have > root privileges, this check should be something along the lines of > ib_safe_file_access() or sg_check_file_access(). > > Checking for uaccess_kernel() prevents the symptom that syzkaller > notices - a user being able to cause a kernel memory access -, but it > doesn't deal with the case where a user opens a file descriptor to > this device and tricks a more privileged process into writing into it > (e.g. by passing it to a suid binary as stdout or stderr). > Yep, I'll do that. > Looking closer, I wonder whether this kind of behavior is limited to > the UHID_CREATE request, which has a comment on it saying "/* > Obsolete! Use UHID_CREATE2. */". If we could keep this kind of ugly > kludge away from the code paths you're supposed to be using, that > would be nice... > I wanted to be careful, but yes AFAICS it can be limited to UHID_CREATE only, so I'll do that instead. - Eric