netdev - Re: [PATCH 03/24] net: add a new sockptr

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Message-ID: <20200722075620.GA26554@lst.de>
Date:   Wed, 22 Jul 2020 09:56:20 +0200
From:   Christoph Hellwig <hch@....de>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     Christoph Hellwig <hch@....de>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Eric Dumazet <edumazet@...gle.com>,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        linux-sctp@...r.kernel.org, linux-hams@...r.kernel.org,
        linux-bluetooth@...r.kernel.org, bridge@...ts.linux-foundation.org,
        linux-can@...r.kernel.org, dccp@...r.kernel.org,
        linux-decnet-user@...ts.sourceforge.net,
        linux-wpan@...r.kernel.org, linux-s390@...r.kernel.org,
        mptcp@...ts.01.org, lvs-devel@...r.kernel.org,
        rds-devel@....oracle.com, linux-afs@...ts.infradead.org,
        tipc-discussion@...ts.sourceforge.net, linux-x25@...r.kernel.org
Subject: Re: [PATCH 03/24] net: add a new sockptr_t type

On Mon, Jul 20, 2020 at 10:55:43AM -0700, Eric Biggers wrote:
> On Mon, Jul 20, 2020 at 07:43:22PM +0200, Christoph Hellwig wrote:
> > On Mon, Jul 20, 2020 at 09:37:48AM -0700, Eric Biggers wrote:
> > > How does this not introduce a massive security hole when
> > > CONFIG_ARCH_HAS_NON_OVERLAPPING_ADDRESS_SPACE?
> > > 
> > > AFAICS, userspace can pass in a pointer >= TASK_SIZE,
> > > and this code makes it be treated as a kernel pointer.
> > 
> > Yeah, we'll need to validate that before initializing the pointer.
> > 
> > But thinking this a little further:  doesn't this mean any
> > set_fs(KERNEL_DS) that has other user pointers than the one it is
> > intended for has the same issue?  Pretty much all of these are gone
> > in mainline now, but in older stable kernels there might be some
> > interesting cases, especially in the compat ioctl handlers.
> 
> Yes.  I thought that eliminating that class of bug is one of the main
> motivations for your "remove set_fs" work.  See commit 128394eff343
> ("sg_write()/bsg_write() is not fit to be called under KERNEL_DS") for a case
> where this type of bug was fixed.
> 
> Are you aware of any specific cases that weren't already fixed?  If there are
> any, they need to be urgently fixed.

current mainline has almost no set_fs left, and setsockopt seems
pretty much safe.  But if we go back a long term stable release or two
I bet I'd find one or two.