netdev - [PATCH 2/3] virtio_ring: check used

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Date:	Thu, 5 May 2011 18:08:10 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Carsten Otte <cotte@...ibm.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	linux390@...ibm.com, Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Shirley Ma <xma@...ibm.com>, lguest@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
	linux-s390@...r.kernel.org, kvm@...r.kernel.org,
	Krishna Kumar <krkumar2@...ibm.com>,
	Tom Lendacky <tahm@...ux.vnet.ibm.com>, steved@...ibm.com,
	habanero@...ux.vnet.ibm.com
Subject: [PATCH 2/3] virtio_ring: check used_event offset

Nothing's wrong with vring_size as is, but it's nice
to check that the new field in the avail ring
won't overlow into the used ring.

Reported-by: Tom Lendacky <tahm@...ux.vnet.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---
 include/linux/virtio_ring.h |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index 2a3b0ea..089cbf2 100644
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h
@@ -119,7 +119,13 @@ static inline void vring_init(struct vring *vr, unsigned int num, void *p,
 
 static inline unsigned vring_size(unsigned int num, unsigned long align)
 {
-	return ((sizeof(struct vring_desc) * num + sizeof(__u16) * (2 + num)
+#ifdef __KERNEL__
+	/* Older versions did not have used_event field at the end of the
+	 * avail ring. Used ring offset must be compatible with such devices. */
+	size_t s = sizeof(struct vring_desc) * num + sizeof(__u16) * (2 + num);
+	BUG_ON(ALIGN(s, align) != ALIGN(s + sizeof(__u16), align));
+#endif
+	return ((sizeof(struct vring_desc) * num + sizeof(__u16) * (3 + num)
 		 + align - 1) & ~(align - 1))
 		+ sizeof(__u16) * 3 + sizeof(struct vring_used_elem) * num;
 }
-- 
1.7.5.53.gc233e

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