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blkback: Fix CVE-2010-3699

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A guest can cause the backend driver to leak a kernel thread. Such
leaked threads hold references to the device, whichmakes the device
impossible to tear down. If shut down, the guest remains a zombie
domain, the xenwatch process hangs, and most xm commands will stop
working.

This patch tries to do the following for blkback:
    - identify/extract idempotent teardown operations,
    - add/move the invocation of said teardown operation
      right before we're about to allocate new resources in the
      Connected states.

[ linux-2.6.18-xen.hg 59f097ef181b ]

Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Keir Fraser <keir@xen.org>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
This commit is contained in:
Keir Fraser 2010-11-24 22:08:20 -08:00 committed by Konrad Rzeszutek Wilk
parent a81135d90b
commit 313d7b003c
1 changed files with 6 additions and 0 deletions
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6
drivers/xen/blkback/xenbus.c
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@ -382,6 +382,11 @@ static void frontend_changed(struct xenbus_device *dev,
if (dev->state == XenbusStateConnected)
break;
/* Enforce precondition before potential leak point.
* blkif_disconnect() is idempotent.
*/
blkif_disconnect(be->blkif);
err = connect_ring(be);
if (err)
break;
@ -399,6 +404,7 @@ static void frontend_changed(struct xenbus_device *dev,
break;
/* fall through if not online */
case XenbusStateUnknown:
/* implies blkif_disconnect() via blkback_remove() */
device_unregister(&dev->dev);
break;