Patch "vhost: fix initialization for vq->is_le" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

    vhost: fix initialization for vq->is_le

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
vhost-fix-initialization-for-vq-is_le.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Halil Pasic <[email protected]>
Date: Mon, 30 Jan 2017 11:09:36 +0100
Subject: vhost: fix initialization for vq->is_le

From: Halil Pasic <[email protected]>

commit cda8bba0f99d25d2061c531113c14fa41effc3ae upstream.

Currently, under certain circumstances vhost_init_is_le does just a part of the initialization job, and depends on vhost_reset_is_le being called too. For this reason vhost_vq_init_access used to call vhost_reset_is_le when vq->private_data is NULL. This is not only counter intuitive, but also real a problem because it breaks vhost_net. The bug was introduced to vhost_net with commit 2751c9882b94 ("vhost: cross-endian support for legacy devices"). The symptom is corruption of the vq's used.idx field (virtio) after VHOST_NET_SET_BACKEND was issued as a part of the vhost shutdown on a vq with pending descriptors.

Let us make sure the outcome of vhost_init_is_le never depend on the state it is actually supposed to initialize, and fix virtio_net by removing the reset from vhost_vq_init_access.

With the above, there is no reason for vhost_reset_is_le to do just half of the job. Let us make vhost_reset_is_le reinitialize is_le.

---
 drivers/vhost/vhost.c |   10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

@@ -130,14 +130,14 @@ static long vhost_get_vring_endian(struc
 
 static void vhost_init_is_le(struct vhost_virtqueue *vq)
 {
-	if (vhost_has_feature(vq, VIRTIO_F_VERSION_1))
-		vq->is_le = true;
+	vq->is_le = vhost_has_feature(vq, VIRTIO_F_VERSION_1)
+		|| virtio_legacy_is_little_endian();
 }
 #endif /* CONFIG_VHOST_CROSS_ENDIAN_LEGACY */
 
 static void vhost_reset_is_le(struct vhost_virtqueue *vq)
 {
-	vq->is_le = virtio_legacy_is_little_endian();
+	vhost_init_is_le(vq);
 }
 
 struct vhost_flush_struct {

@@ -1713,10 +1713,8 @@ int vhost_vq_init_access(struct vhost_vi
 	int r;
 	bool is_le = vq->is_le;
 
-	if (!vq->private_data) {
-		vhost_reset_is_le(vq);
+	if (!vq->private_data)
 		return 0;
-	}
 
 	vhost_init_is_le(vq);
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/vhost-fix-initialization-for-vq-is_le.patch