Hardy SRU, xen unified block-device I/O interface back end can orphan devices, CVE-2010-3699
Stefan Bader
stefan.bader at canonical.com
Wed Jan 26 16:45:30 UTC 2011
Scary, this sort of pulls in silently a few other changes to Xen, which makes it
even harder.
On 01/26/2011 03:16 PM, Tim Gardner wrote:
> The following changes since commit 11e175fe9030a484684a34f0b13040bf93ef2290:
> Dan Rosenberg (1):
> V4L/DVB: ivtvfb: prevent reading uninitialized stack memory, CVE-2010-4079
>
> are available in the git repository at:
>
> git://kernel.ubuntu.com/rtg/ubuntu-hardy.git CVE-2010-3699
>
> Tim Gardner (1):
> UBUNTU: xen unified block-device I/O interface back end can orphan devices, CVE-2010-3699
>
> .../xen/patchset/020-xen-CVE-2010-3699.patch | 152 ++++++++++++++++++++
> 1 files changed, 152 insertions(+), 0 deletions(-)
> create mode 100644 debian/binary-custom.d/xen/patchset/020-xen-CVE-2010-3699.patch
>
> From a42d61170c261228e31c95b98e42ec80444638d8 Mon Sep 17 00:00:00 2001
> From: Tim Gardner <tim.gardner at canonical.com>
> Date: Tue, 25 Jan 2011 14:54:33 -0700
> Subject: [PATCH] UBUNTU: xen unified block-device I/O interface back end can orphan devices, CVE-2010-3699
>
> Excerpted from http://rhn.redhat.com/errata/RHSA-2011-0004.html:
>
> "A flaw was found in the Xenbus code for the unified block-device I/O
> interface back end. A privileged guest user could use this flaw to cause a
> denial of service on the host system running the Xen hypervisor."
>
> Most of this patch was developed from http://xenbits.xensource.com/linux-2.6.18-xen.hg?rev/59f097ef181b.
> A careful comparision of the patch and the actual contents of http://xenbits.xensource.com/linux-2.6.18-xen.hg
> showed that part of the original patch introduced a regression as can be seen from the Mercurial log.
> I've not implemented that piece of the patch.
>
> Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
> ---
> .../xen/patchset/020-xen-CVE-2010-3699.patch | 152 ++++++++++++++++++++
> 1 files changed, 152 insertions(+), 0 deletions(-)
> create mode 100644 debian/binary-custom.d/xen/patchset/020-xen-CVE-2010-3699.patch
>
> diff --git a/debian/binary-custom.d/xen/patchset/020-xen-CVE-2010-3699.patch b/debian/binary-custom.d/xen/patchset/020-xen-CVE-2010-3699.patch
> new file mode 100644
> index 0000000..57dea44
> --- /dev/null
> +++ b/debian/binary-custom.d/xen/patchset/020-xen-CVE-2010-3699.patch
> @@ -0,0 +1,152 @@
> +diff --git a/drivers/xen/blkback/xenbus.c b/drivers/xen/blkback/xenbus.c
> +index f9feb43..1611d7a 100644
> +--- a/drivers/xen/blkback/xenbus.c
> ++++ b/drivers/xen/blkback/xenbus.c
> +@@ -362,6 +362,11 @@ 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;
> +@@ -379,6 +384,7 @@ 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;
> +
> +diff --git a/drivers/xen/blktap/xenbus.c b/drivers/xen/blktap/xenbus.c
> +index f9e3159..d5db1b5 100644
> +--- a/drivers/xen/blktap/xenbus.c
> ++++ b/drivers/xen/blktap/xenbus.c
> +@@ -326,6 +326,18 @@ static void tap_backend_changed(struct xenbus_watch *watch,
> + tap_update_blkif_status(be->blkif);
> + }
> +
> ++
> ++static void tap_blkif_disconnect(blkif_t *blkif)
> ++{
> ++ if (blkif->xenblkd) {
> ++ kthread_stop(blkif->xenblkd);
> ++ blkif->xenblkd = NULL;
> ++ }
> ++
> ++ /* idempotent */
> ++ tap_blkif_free(blkif);
Maybe this is giving grief. In our version tap_blkif_free() is also calling
kmem_cache_free, while the version in the repo has this factored out into a
separate function which is only called on blktap_remove()
> ++}
> ++
> + /**
> + * Callback received when the frontend's state changes.
> + */
> +@@ -354,6 +366,11 @@ static void tap_frontend_changed(struct xenbus_device *dev,
> + if (dev->state == XenbusStateConnected)
> + break;
> +
> ++ /* Enforce precondition before potential leak point.
> ++ * tap_blkif_disconnect() is idempotent.
> ++ */
> ++ tap_blkif_disconnect(be->blkif);
> ++
> + err = connect_ring(be);
> + if (err)
> + break;
> +@@ -361,10 +378,7 @@ static void tap_frontend_changed(struct xenbus_device *dev,
> + break;
> +
> + case XenbusStateClosing:
> +- if (be->blkif->xenblkd) {
> +- kthread_stop(be->blkif->xenblkd);
> +- be->blkif->xenblkd = NULL;
> +- }
> ++ tap_blkif_disconnect(be->blkif);
> + xenbus_switch_state(dev, XenbusStateClosing);
> + break;
> +
> +@@ -374,6 +388,9 @@ static void tap_frontend_changed(struct xenbus_device *dev,
> + break;
> + /* fall through if not online */
> + case XenbusStateUnknown:
> ++ /* Implies the effects of blkif_disconnect() via
> ++ * blktap_remove().
> ++ */
> + device_unregister(&dev->dev);
> + break;
> +
> +diff --git a/drivers/xen/netback/xenbus.c b/drivers/xen/netback/xenbus.c
> +index b55005c..fb84b4b 100644
> +--- a/drivers/xen/netback/xenbus.c
> ++++ b/drivers/xen/netback/xenbus.c
> +@@ -32,6 +32,7 @@
> + static int connect_rings(struct backend_info *);
> + static void connect(struct backend_info *);
> + static void backend_create_netif(struct backend_info *be);
> ++static void netback_disconnect(struct device *);
> +
> + static int netback_remove(struct xenbus_device *dev)
> + {
> +@@ -39,15 +40,22 @@ static int netback_remove(struct xenbus_device *dev)
> +
> + netback_remove_accelerators(be, dev);
> +
> +- if (be->netif) {
> +- netif_disconnect(be->netif);
> +- be->netif = NULL;
> +- }
> ++ netback_disconnect(&dev->dev);
> + kfree(be);
> + dev->dev.driver_data = NULL;
> + return 0;
> + }
> +
> ++static void netback_disconnect(struct device *xbdev_dev)
> ++{
> ++ struct backend_info *be = xbdev_dev->driver_data;
> ++
> ++ if (be->netif) {
> ++ kobject_uevent(&xbdev_dev->kobj, KOBJ_OFFLINE);
> ++ netif_disconnect(be->netif);
> ++ be->netif = NULL;
> ++ }
> ++}
> +
> + /**
> + * Entry point to this code when a new device is created. Allocate the basic
> +@@ -225,16 +233,17 @@ static void frontend_changed(struct xenbus_device *dev,
> + break;
> +
> + case XenbusStateConnected:
> ++ if (dev->state == XenbusStateConnected)
> ++ break;
> ++
> ++ /* backend_create_netif() is idempotent */
> + backend_create_netif(be);
> + if (be->netif)
> + connect(be);
> + break;
> +
> + case XenbusStateClosing:
> +- if (be->netif) {
> +- netif_disconnect(be->netif);
> +- be->netif = NULL;
> +- }
> ++ netback_disconnect(&dev->dev);
> + xenbus_switch_state(dev, XenbusStateClosing);
> + break;
> +
> +@@ -244,8 +253,7 @@ static void frontend_changed(struct xenbus_device *dev,
> + break;
> + /* fall through if not online */
> + case XenbusStateUnknown:
> +- if (be->netif != NULL)
> +- kobject_uevent(&dev->dev.kobj, KOBJ_OFFLINE);
> ++ /* implies netback_disconnect() via netback_remove() */
> + device_unregister(&dev->dev);
> + break;
> +
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