Commit c31ecf6c authored Dec 18, 2015 by Konrad Rzeszutek Wilk

xen/blkfront: Fix crash if backend doesn't follow the right states.



We have split the setting up of all the resources in two steps:
1) talk_to_blkback  - which figures out the num_ring_pages (from
   the default value of zero), sets up shadow and so
2) blkfront_connect - does the real part of filling out the
   internal structures.

The problem is if we bypass the 1) step and go straight to 2)
and call blkfront_setup_indirect where we use the macro
BLK_RING_SIZE - which returns an negative value (because
sz is zero  - since num_ring_pages is zero - since it has never
been set).

We can fix this by making sure that we always have called
talk_to_blkback before going to blkfront_connect.

Or we could set in blkfront_probe info->nr_ring_pages = 1
to have a default value. But that looks odd - as we haven't
actually negotiated any ring size.

This patch changes XenbusStateConnected state to detect if
we haven't done the initial handshake - and if so continue
on as if were in XenbusStateInitWait state.

We also roll the error recovery (freeing the structure) into
talk_to_blkback error path - which is safe since that function
is only called from blkback_changed.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

parent 93bb277f

drivers/block/xen-blkfront.c

+8 −4

Original line number	Diff line number	Diff line
		@@ -1867,6 +1867,9 @@ static int talk_to_blkback(struct xenbus_device *dev,
		destroy_blkring:
		blkif_free(info, 0);

		kfree(info);
		dev_set_drvdata(&dev->dev, NULL);

		return err;
		}

		@@ -2453,11 +2456,8 @@ static void blkback_changed(struct xenbus_device *dev,
		case XenbusStateInitWait:
		if (dev->state != XenbusStateInitialising)
		break;
		if (talk_to_blkback(dev, info)) {
		kfree(info);
		dev_set_drvdata(&dev->dev, NULL);
		if (talk_to_blkback(dev, info))
		break;
		}
		case XenbusStateInitialising:
		case XenbusStateInitialised:
		case XenbusStateReconfiguring:
		@@ -2466,6 +2466,10 @@ static void blkback_changed(struct xenbus_device *dev,
		break;

		case XenbusStateConnected:
		if (dev->state != XenbusStateInitialised) {
		if (talk_to_blkback(dev, info))
		break;
		}
		blkfront_connect(info);
		break;