linux-kernel - [PATCH] vhost/net: length miscalculation

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Message-ID: <1420620847-24477-1-git-send-email-mst@redhat.com>
Date:	Wed, 7 Jan 2015 10:55:55 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	Alex Williamson <alex.williamson@...hat.com>,
	Greg Kurz <gkurz@...ux.vnet.ibm.com>, kvm@...r.kernel.org,
	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: [PATCH] vhost/net: length miscalculation

commit 8b38694a2dc8b18374310df50174f1e4376d6824
    vhost/net: virtio 1.0 byte swap
had this chunk:
-       heads[headcount - 1].len += datalen;
+       heads[headcount - 1].len = cpu_to_vhost32(vq, len - datalen);

This adds datalen with the wrong sign, causing guest panics.

Fixes: 8b38694a2dc8b18374310df50174f1e4376d6824
Reported-by: Alex Williamson <alex.williamson@...hat.com>
Suggested-by: Greg Kurz <gkurz@...ux.vnet.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---

Alex, could you please confirm this fixes the crash for you?

 drivers/vhost/net.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 14419a8..d415d69 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -538,7 +538,7 @@ static int get_rx_bufs(struct vhost_virtqueue *vq,
 		++headcount;
 		seg += in;
 	}
-	heads[headcount - 1].len = cpu_to_vhost32(vq, len - datalen);
+	heads[headcount - 1].len = cpu_to_vhost32(vq, len + datalen);
 	*iovcount = seg;
 	if (unlikely(log))
 		*log_num = nlogs;
-- 
MST
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