From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S935375AbdKPOBa (ORCPT <rfc822;w@1wt.eu>);
        Thu, 16 Nov 2017 09:01:30 -0500
Received: from shards.monkeyblade.net ([184.105.139.130]:44106 "EHLO
        shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S935281AbdKPOAc (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Thu, 16 Nov 2017 09:00:32 -0500
Date: Thu, 16 Nov 2017 23:00:26 +0900 (KST)
Message-Id: <20171116.230026.45581437273132607.davem@davemloft.net>
To: ebiederm@xmission.com
Cc: keescook@chromium.org, eric.dumazet@gmail.com, kcc@google.com,
        andreyknvl@google.com, edumazet@google.com, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, security@kernel.org, glider@google.com,
        linux-sctp@vger.kernel.org, nhorman@tuxdriver.com, vyasevich@gmail.com
Subject: Re: [PATCH net] net/sctp: Always set scope_id in
 sctp_inet6_skb_msgname
From: David Miller <davem@davemloft.net>
In-Reply-To: <871skyzwk3.fsf_-_@xmission.com>
References: <CAGXu5jJAepjBcLki0G-fa4JNH93szZAoWWFORvo3zxPWDQLjGQ@mail.gmail.com>
        <CAG_fn=UUB6ep_hdiQq7CyGUnc93R-13mGZERyM-yi3b11hLRdQ@mail.gmail.com>
        <871skyzwk3.fsf_-_@xmission.com>
X-Mailer: Mew version 6.7 on Emacs 25.3 / Mule 6.0 (HANACHIRUSATO)
Mime-Version: 1.0
Content-Type: Text/Plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.5.12 (shards.monkeyblade.net [149.20.54.216]); Thu, 16 Nov 2017 06:00:32 -0800 (PST)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

From: ebiederm@xmission.com (Eric W. Biederman)
Date: Wed, 15 Nov 2017 22:17:48 -0600

> 
> Alexandar Potapenko while testing the kernel with KMSAN and syzkaller
> discovered that in some configurations sctp would leak 4 bytes of
> kernel stack.
> 
> Working with his reproducer I discovered that those 4 bytes that
> are leaked is the scope id of an ipv6 address returned by recvmsg.
> 
> With a little code inspection and a shrewd guess I discovered that
> sctp_inet6_skb_msgname only initializes the scope_id field for link
> local ipv6 addresses to the interface index the link local address
> pertains to instead of initializing the scope_id field for all ipv6
> addresses.
> 
> That is almost reasonable as scope_id's are meaniningful only for link
> local addresses.  Set the scope_id in all other cases to 0 which is
> not a valid interface index to make it clear there is nothing useful
> in the scope_id field.
> 
> There should be no danger of breaking userspace as the stack leak
> guaranteed that previously meaningless random data was being returned.
> 
> Fixes: 372f525b495c ("SCTP:  Resync with LKSCTP tree.")
> History-tree: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
> Reported-by: Alexander Potapenko <glider@google.com>
> Tested-by: Alexander Potapenko <glider@google.com>
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

Applied and queued up for -stable, thanks Eric.