[PATCH 3.8 64/91] vhost/scsi: Fix incorrect usage of get_user_pages_fast write parameter

Kamal Mostafa kamal at canonical.com
Fri Nov 8 02:15:19 UTC 2013 -stable review patch.  If anyone has any objections, please let me know.


From: Nicholas Bellinger <nab at linux-iscsi.org>

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 at redhat.com>
Cc: Michael S. Tsirkin <mst at redhat.com>
Cc: Asias He <asias at redhat.com>
Signed-off-by: Nicholas Bellinger <nab at linux-iscsi.org>
[ kamal: backport to 3.8 (applied to tcm_vhost.c) ]
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
 drivers/vhost/tcm_vhost.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/vhost/tcm_vhost.c b/drivers/vhost/tcm_vhost.c
index 22321cf..9412440 100644
--- a/drivers/vhost/tcm_vhost.c
+++ b/drivers/vhost/tcm_vhost.c
@@ -696,7 +696,7 @@ 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");
 				break; /* TODO */

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