linux-kernel - Re: [PATCH 1/4] inet: Add skb_copy_datagram

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Date:	Sun, 9 Nov 2014 21:19:08 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	David Miller <davem@...hat.com>
Cc:	herbert@...dor.apana.org.au, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, bcrl@...ck.org,
	"Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH 1/4] inet: Add skb_copy_datagram_iter

[Michael Cc'd]

On Fri, Nov 07, 2014 at 11:42:53PM +0000, Al Viro wrote:

> I'll finish RTFS drivers/vhost and if it turns out to be OK I'll post the
> series moving those checks to the moment of copying iovec from userland,
> so that kernel-side we could always rely on ->msg_iov elements having been
> verified.

Two questions:
1) does sparc64 access_ok() need to differ for 32bit and 64bit tasks?
AFAICS, x86 and ppc just check that address is OK for 64bit process -
if a 32bit process passes the kernel an address that would be valid
for 64bit process, but not for 32bit one, we just get a pagefault in
__copy_from_user() and friends.  No kernel objects are going to have
a virtual address in that range, so access_ok() doesn't bother preventing
such access attempts there...

2) shouldn't vhost_dev_cleanup() stop the worker thread before doing anything
else?  AFAICS, we do parts of vhost_dev teardown while the thread is
still running; granted, we keep dev->mm pinned down until after it stops
(or we would be _really_ screwed), but is it safe to do all those fput()s, etc.
while it's still running?  Michael?
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