vhost/scsi: Fix incorrect usage of get_user_pages_fast write parameter

commit 60a01f558af9c48b0bb31f303c479e32721add3f upstream.

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 -> READ payload case, and *not*
for the virtio-scsi DMA_TO_DEVICE -> 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 <stefanha@redhat.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Asias He <asias@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 7014202972259f4d7046d5f4a110fe9a0cedef37..962c7e3c3baabf4de83ad50519a5ca8398d13bb8 100644 (file)
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -1017,7 +1017,7 @@ static void vhost_scsi_handle_vq(struct vhost_scsi *vs,
                if (data_direction != DMA_NONE) {
                        ret = vhost_scsi_map_iov_to_sgl(tv_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;