linux-kernel - [PATCH] vhost/scsi: Fix incorrect usage of get_user_pages

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Message-Id: <1382724436-28478-1-git-send-email-nab@linux-iscsi.org>
Date:	Fri, 25 Oct 2013 18:07:16 +0000
From:	"Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To:	target-devel <target-devel@...r.kernel.org>
Cc:	lf-virt <virtualization@...ts.linux-foundation.org>,
	kvm-devel <kvm@...r.kernel.org>,
	linux-scsi <linux-scsi@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Stefan Hajnoczi <stefanha@...hat.com>,
	"Michael S. Tsirkin" <mst@...hat.com>, Asias He <asias@...hat.com>,
	Nicholas Bellinger <nab@...ux-iscsi.org>
Subject: [PATCH] vhost/scsi: Fix incorrect usage of get_user_pages_fast write parameter

From: Nicholas Bellinger <nab@...ux-iscsi.org>

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@...hat.com>
Cc: Michael S. Tsirkin <mst@...hat.com>
Cc: Asias He <asias@...hat.com>
Cc: <stable@...r.kernel.org> # 3.6+
Signed-off-by: Nicholas Bellinger <nab@...ux-iscsi.org>
---
 drivers/vhost/scsi.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index ce5221f..e663921 100644
--- 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;
-- 
1.7.2.5

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