netdev - drivers/vhost: sizing of ubuf

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Message-ID: <87hakmwqd6.fsf@rustcorp.com.au>
Date:	Fri, 08 Mar 2013 13:57:09 +1100
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	<mst@...hat.com>
CC:	<virtualization@...ts.linux-foundation.org>,
	<netdev@...r.kernel.org>
Subject: drivers/vhost: sizing of ubuf_info and heads

Hi Michael,

        I'm a bit confused about why ubuf_info and heads are UIO_MAXIOV
length arrays, rather than being the size of the ring?  In particular,
this is suspicious:

linux/drivers/vhost/net.c:342:	struct ubuf_info *ubuf = &vq->ubuf_info[head];

And it seems to assume we trust head: a malicious guest could put the
same head entry in the ring twice, and we will get two callbacks on the
same value.  I don't know what that will do, but I'm not sure it's
harmless.

Thanks,
Rusty.
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