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From: Paolo Bonzini <pbonzini@redhat.com>
To: qemu-stable@nongnu.org
Date: Wed, 11 Jan 2012 10:48:33 +0100
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Subject: [Qemu-stable] [PATCH] virtio-blk: refuse SG_IO requests with
	scsi=off
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QEMU does have a "scsi" option (to be used like -device
virtio-blk-pci,drive=foo,scsi=off).  However, it only
masks the feature bit, and does not reject the command
if a malicious guest disregards the feature bits and
issues a request.

Without this patch, using scsi=off does not protect you
from CVE-2011-4127.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 hw/virtio-blk.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/hw/virtio-blk.c b/hw/virtio-blk.c
index b70d116..6cd3164 100644
--- a/hw/virtio-blk.c
+++ b/hw/virtio-blk.c
@@ -153,6 +153,12 @@ static void virtio_blk_handle_scsi(VirtIOBlockReq *req)
     int status;
     int i;
 
+    if ((req->dev->vdev.guest_features & (1 << VIRTIO_BLK_F_SCSI)) == 0) {
+        virtio_blk_req_complete(req, VIRTIO_BLK_S_UNSUPP);
+        qemu_free(req);
+        return;
+    }
+
     /*
      * We require at least one output segment each for the virtio_blk_outhdr
      * and the SCSI command block.
-- 
1.7.7.1