Re: [PATCH 03/24] net: add a new sockptr_t type

To: Christoph Hellwig <hch@xxxxxx>
Subject: Re: [PATCH 03/24] net: add a new sockptr_t type
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>, Jakub Kicinski <kuba@xxxxxxxxxx>, Alexei Starovoitov <ast@xxxxxxxxxx>, Daniel Borkmann <daniel@xxxxxxxxxxxxx>, Alexey Kuznetsov <kuznet@xxxxxxxxxxxxx>, Hideaki YOSHIFUJI <yoshfuji@xxxxxxxxxxxxxx>, Eric Dumazet <edumazet@xxxxxxxxxx>, linux-crypto@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, netdev@xxxxxxxxxxxxxxx, bpf@xxxxxxxxxxxxxxx, netfilter-devel@xxxxxxxxxxxxxxx, coreteam@xxxxxxxxxxxxx, linux-sctp@xxxxxxxxxxxxxxx, linux-hams@xxxxxxxxxxxxxxx, linux-bluetooth@xxxxxxxxxxxxxxx, bridge@xxxxxxxxxxxxxxxxxxxxxxxxxx, linux-can@xxxxxxxxxxxxxxx, dccp@xxxxxxxxxxxxxxx, linux-decnet-user@xxxxxxxxxxxxxxxxxxxxx, linux-wpan@xxxxxxxxxxxxxxx, linux-s390@xxxxxxxxxxxxxxx, mptcp@xxxxxxxxxxxx, lvs-devel@xxxxxxxxxxxxxxx, rds-devel@xxxxxxxxxxxxxx, linux-afs@xxxxxxxxxxxxxxxxxxx, tipc-discussion@xxxxxxxxxxxxxxxxxxxxx, linux-x25@xxxxxxxxxxxxxxx
From: Eric Biggers <ebiggers@xxxxxxxxxx>
Date: Mon, 20 Jul 2020 10:55:43 -0700
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
> > 
> > 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.

- Eric

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