linux-kernel - [PATCH] Fix used_idx wrap-around in virtio

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Message-Id: <11944721642196-git-send-email-aliguori@us.ibm.com>
Date:	Wed,  7 Nov 2007 15:49:24 -0600
From:	Anthony Liguori <aliguori@...ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	Anthony Liguori <aliguori@...ibm.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	virtualization@...ts.linux-foundation.org
Subject: [PATCH] Fix used_idx wrap-around in virtio

The more_used() function compares the vq->vring.used->idx with last_used_idx.
Since vq->vring.used->idx is a 16-bit integer, and last_used_idx is an
unsigned int, this results in unpredictable behavior when vq->vring.used->idx
wraps around.

This patch corrects this by changing last_used_idx to the correct type.

Signed-off-by: Anthony Liguori <aliguori@...ibm.com>

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 0e4baca..0e1bf05 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -53,7 +53,7 @@ struct vring_virtqueue
 	unsigned int num_added;

 	/* Last used index we've seen. */
-	unsigned int last_used_idx;
+	u16 last_used_idx;

 	/* How to notify other side. FIXME: commonalize hcalls! */
 	void (*notify)(struct virtqueue *vq);
-
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