vhost/scsi: Fix incorrect usage of get_user_pages_fast write parameter

Nicholas Bellinger · Nicholas Bellinger · commit 60a01f558af9 · 2013-10-25T11:03:34.000-07:00
This patch addresses a long-standing bug where the get_user_pages_fast()
write parameter used for setting the underlying page table entry permission
bits was incorrectly set to write=1 for data_direction=DMA_TO_DEVICE, and
passed into get_user_pages_fast() via vhost_scsi_map_iov_to_sgl().

However, this parameter is intended to signal WRITEs to pinned userspace
PTEs for the virtio-scsi DMA_FROM_DEVICE -&gt; READ payload case, and *not*
for the virtio-scsi DMA_TO_DEVICE -&gt; WRITE payload case.

This bug would manifest itself as random process segmentation faults on
KVM host after repeated vhost starts + stops and/or with lots of vhost
endpoints + LUNs.

Cc: Stefan Hajnoczi &lt;stefanha@redhat.com&gt;
Cc: Michael S. Tsirkin &lt;mst@redhat.com&gt;
Cc: Asias He &lt;asias@redhat.com&gt;
Cc: &lt;stable@vger.kernel.org&gt; # 3.6+
Signed-off-by: Nicholas Bellinger &lt;nab@linux-iscsi.org&gt;
diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
@@ -1056,7 +1056,7 @@ vhost_scsi_handle_vq(struct vhost_scsi *vs, struct vhost_virtqueue *vq)
 		if (data_direction != DMA_NONE) {
 			ret = vhost_scsi_map_iov_to_sgl(cmd,
 					&vq->iov[data_first], data_num,
-					data_direction == DMA_TO_DEVICE);
+					data_direction == DMA_FROM_DEVICE);
 			if (unlikely(ret)) {
 				vq_err(vq, "Failed to map iov to sgl\n");
 				goto err_free;
