From c31ecf6c126dbc7f30234eaf6c4a079649a38de7 Mon Sep 17 00:00:00 2001 From: Konrad Rzeszutek Wilk Date: Fri, 18 Dec 2015 16:28:53 -0500 Subject: [PATCH] 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 --- drivers/block/xen-blkfront.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c index f3d0d4758641..8a8dc91c39f7 100644 --- a/drivers/block/xen-blkfront.c +++ b/drivers/block/xen-blkfront.c @@ -1867,6 +1867,9 @@ again: 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; -- 2.20.1